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And a ioi SONODYNE UMUftiji check the quality of music you're recording, Then there's an AM/FM stereo tuner for music around the world. A 12-band graphic equalizer that lets you engineer your own sound. A sleek, belt driven, automatic turntable And best of all, India’s hottest selling SX-606 bass rellex speaker system that unleashes rich, pure, dreamy sound. So even if you're tempted to buy Uranus for its looks alone, do give it a hearing. After all, what's really stunning about it is its sound. The sound of Sonodyne. Uranus is a totality ol the SO- 520 cassette Seek SA-520 when it’s quiet. Electronics technology Air defence systems for countries and continents 11 .23 Jockeying for supremacy in Europe's own space race 11.36 How much longer will silicon be used? 11.40 Projects Computerscope - 1 11.18 Voltage comparison on a scope 11 .25 IDU for satellite TV reception -1 11 .26 RF circuit design 11.38 Dark-room exposure meter 11.44 High-power AF amplifier - 2 1 1 .46 Information News and views 11-16 New products 11.62 Corrections 1 1 .74 Guide lines Classified ads 11.74 Index of advertisers 1 1 74 Selex - 17 Measuring Techniques (chapter-3) 11.55 Measuring power with a Multimeter 11 .57 Power Calculations 11.60 ill -03 YOUR SEARCH IS OVER FOR SOLDER WIRES & STICKS SWASTIK a Hfnttf sijtiangnwu* "•ith ya/.f/ (f nft/r, ® Low meltins point • Minimum resistance • No dry solder • Resonably priced Swastik Smelting Co Shiv Shakti Enterprises 205-B Shreyas Industrial Estate Off Western Express Highway, Goregaon (E) Bombay - 400 063 Ph 68 45 37 C-1B/2101/4, GIDC Industrial Estate Halol - 389350, Dist. 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Specifications Rated capacitance 1500 pF — 0.82 pF Tolerance ±5%&±10% Rated voltage (dc) 250-630.1000, 1500, 2000 Volts Rated temp. 85°C Climatic category . I EC 68 40/085/56 information on Yes, rush me — Philips POLYPROPYLENE CAPACITORS Name: Designation: Area of Application: Company Address: Philips India Elcoma Division, Band Box Building, 254, D. Dr. Annie Besant Road, Worli, Bombay-400 025 Philips -the trusted Indian household name for over fifty years ill -07 lAL |VHCRgFcoSP BOL ersSSS^SV.i SC®- pA T ^ USING | ON 4 a/ipacT ' 1 Microprocessor Training & Development System With Built-in Important Features: ■ Eight Channel ADC with 100 micro seconds conversion time. ■ Single Channel DAC with 0 to 12 V analog output ■ 8085A CPU @ 3 MHz. ■ Fully decoded Memory and I/O. ■ Battery Back Up for RAM. ■ Powerful Monitor Firmware with ADC/DAC subroutines. ■ Fully buffered STD bus for expansion. ■ On board EPROM programmer. ■ Built in interfaces for ASCII Keyboard. Printer and Cassette Recorder. ■ Eight channel Interrupt Controller with programmable priorities. Options: IK Memory Card with Real Time Clock/Calendar ■ VDU Card with Editor/Assembler/ isembler. ■ FDC Card with CP/M BIOS. ■ ROM bassed FORTH and Tiny BASIC. ICII Keyboard. ■ Video Monitor. ■ Floppy Disc Drives. ■ 80 Column Dot Matrix Printer. IMPACT- 1 can be converted into a powerful Process Control Computer using the expansion cards and optional peripherals offered by us. Introduced for the First Time in India by: Creative Data Systems 14, Hanuman Terrace, Tara Temple Lane, Lamington Road, Bombay 400 007. Tel: 362421, 353029 Tlx: 011-71801 DYNA IN, Gram: ELMADEVICE IMPACT-1 can be customised tetratech for OEM use by : treated, tetratech industrial services Post Box-6860, Vile Parle (East). Bombay 400 057 11-09 Engineering Systems International British Bank of Middle East 2nd Floor, 16, Veer Nariman Road, Fort. Bombay-400 023. Tel: 2049543. 2049584 Grams: ESINTAL LAST TAU60 KP COMPUTER- SCOPE-1 by R v Linden To help those many people whose workshop includes a computer but not an oscilloscope, this article presents a drive unit that enables the computer to be used as an oscilloscope. The idea of using a computer as an oscilloscope is based on the fact that it already has a viewing screen and that it can cope with graphics. All that is required, therefore, is a unit that stores the signal to be measured in a memory, after which the com- puter can read the memory and dis- play the data on the monitor. The article will be in two parts: this month the general layout and the complete circuit will be discussed, while part 2 will deal with the con- struction and the alignment. Block diagram The first section of the unit, ie., the AC-DC switch, attenuator, and ampli- fier, consists of analogue circuits, although the first two are controlled by binary signals. An off-set may be added to the amplifier via a digital- to-analogue converter. The incoming signal is then digi- tized, after which a fast analogue-to- digital converter translates the samples into 7-bit data words that are stored in a random-access memory via a buffer stage. The output of the A-D converter is also applied to a trigger and com- parator. The latter compares the in- stantaneous value of the signal with the preset trigger level. If that level is exceeded, either in a positive or in a negative sense, depending on the preset trigger edge Qeading or trailing), the data is stored in correct sequence in the RAM with the aid of an address counter. The eighth bit of every byte indicates when triggering Fig. I. The block schematic of the computerscope drive unit. Fig. 3. The RAM is divided into two pages: the first is used for storing 256 pre- trigger bytes, and the second for storing 256 post-trigger bytes. A specific trigger bit in- dicates at which instant operation is to be trans- ferred from one to the other. takes place. The memory consists of two parts, each of 256 bytes. The first part holds 256 pre-trigger measuring points, and the second 256 post-trigger measuring points. A comprehensive address ensures that writing to, and reading from, the memory takes place in the correct sequence. Sixteen different time bases, derived from a crystal oscillator, are pro- vided. Communication between the drive unit and the computer is effected via two 8-bit 1-0 buses; this enables most computers to be used. The computerscope is controlled via software. A menu-type layout gives the user the possibility of setting all measuring parameters wit only a few Circuit diagram The input is at the centre of Fig. 2 and is connected direct to the AC- DC switch, which is formed by ca- pacitor C« shunted by D1L relay Ret. The switch is followed by the at- tenuator, which consists of two parts: the first can be arranged to attenuate by a factor 1, 2, or 5. and the second by 1, 10, or 100. The total attenuation is set from the computer by means of multiplexers ICj3 and ICa* Both IC23a and IC23b are controlled via lines Vo and Vv while the mul- tiplexers in IC24 are switched via lines V2 and V» In this manner the sensitivity can be set between 10 mV/div and 5 V/div. At the input of the first divider relays I instead of multiplexers are used because of the maximum allowable voltage here. Diodes D< to D> incl. protect the inputs against too high voltages. A variety of fixed and variable capacitors in the attenuator sections provide compensation when square- wave signals are processed. The signal at the output of the sec- ond attenuator has a maximum value of 80 mVpp. It is then raised to 2 V PP by amplifiers Ai, hi. and Aj, to give a signal that can be processed by the A-D converter at the highest possible resolution. An off-set is added to the signal in A3 to enable a vertical shift across the monitor screen. The off-set is pro- vided by a D-A converter, which is housed in ICn together with the fast A-D converter. The computer sends w 1986 1 1 -1 9 the off-set data to the D-A converter via lines OFo to OFs inch The stan- dard value of the off-set is 1 V when the sample lies exactly within the range of the A-D converter (bear in mind that the converter cannot pro- cess negative values). Only seven of the ten bits available at the D-A converter are used here which, be- cause of the graphics resolution of the computers used, is more than enough. The output signal of As is then ap- plied to a fast A-D converter, which contains a separate comparator for each digital level, i.e. 2S6 in all. The conversion time is, therefore, only 26.3 ns (corresponding to a fre- quency of 38 MHz). The highest clock used is 8 MHz, resulting in 8 samples per period at an input signal of 1 MHz. Because of the arrangement ot me system, only 7 bits are used, which is sufficient for an accurate display. The eighth bit is used for storing the trig- ger data. The reference voltage for the A-D and D-A converters is gener- ated by the IC itself. The only exter- nal component is capacitor Cm T he memory section also needs fast ICs, and in the present circuit Type IMS1420 was chosen. This is a RAM with an access time of 45 ns and a ca- pacity of 4 K x 4 bit. Two of these ICs, ICu and ICh are connected in parallel to give a width of 8 bits. The data lines of the RAMs are connec- ted with the outputs of the A-D con- verter via buffer ICu Of the total memory capacity only 512 bytes are used for data storage: the remainder is available for possible later exten- The digitizing and storing of the samples is taken care of by the clock provided by the time base. Oper- ation of the A-D converter is com- menced at the trailing edge of the clock pulse, and at the same time the address counter of the RAMs is in- creased by 1. The random-access memory con- sists of two pages: page 1 contains address 800 to 0FF. and page 2, ad- dresses 100 to IFF. In the absence of a trigger signal, page i is written to. As soon as a trigger arives, the eighth bit of the relevant byte goes high, when writing is transferred to page 2— see Fig. 3. Once this page is full, writing to the memory stops, and the computer is advised that writing is completed by the READY signal. In this way, there are always 256 pre- trigger and 256 post-trigger sam- pling points. After the computer has read the memory, the next writing cycle can be started. As long as there is old information on page 1, triggering is prevented for 256 clock pulses by signal INH. This is calcu- lated by the computer from the state of the time base. The time base (at the left of Fig. 2) consists of crystal oscillator N.-N?, which is followed by a number of :2 and :S dividers, IC; to ICs inch The computer connects one of the out- puts of the time base to the CLK line of the system via multiplexer ICt Latches IC> to IC.o are provided for the exchange of signals between the drive unit and the computer. Circuits IC? to ICs serve to store data which are sent by the computer to the drive unit via PBo to PB. inch PAo, PA., and PA2 are used as write signals for the three ICs. Circuits IC.s and IC.s form an 8-bit comparator for the trigger signal which is provided (in binary form) by I the computer. As soon as the level of the input signal exceeds that of the trigger, the level at the >0 output of IC.t (pin 5) changes state. The edge of this pulse also indicates whether the input signal exceeded the trig- ger in a positive or in a negative The output signal of the comparator is applied to a dual four-channel multiplexer, IC.?. The first part of this stage enables a choice to be made | between the >0 output of the com- parator and the external trigger input with the aid of the EXT signal. The second section, ICm>, is used to choose between the output of the first multiplexer and the inverted out- put signal, that is, between trig- gering at the leading or at the trailing edge of the input signal. The trigger signal is then fed to bistables FF. and FFt where it is combined with the CLK and INH signals. Bistable FF? also provides the eighth data bit for the RAMs: as soon as the circuit is triggered, its output goes high. The eighth data bit is also clocked in bistable FF? , after which it is used as ninth address bit for the memory via multiplexer IC20.. During reading, the circuit is switched via IC20a to the INH signal as ninth address line, whereas dur- ing writing, the output of FFi is used for this purpose. When the ninth address bit becomes logic 1. the address counter is reset via network R3-C1 Control signals The connections between the drive -21 urn! and the computer are shown in Fig. 4. A total of 17 port lines are used: PAe to PA:, PBe to PB:, and CAi. Signal MAN enables manual trig- gering via the keyboard. Bistable FF; is then set via N«, which gate ensures that the MAN signal and the CLK signal in the drive unit are syn- chronized. CPUL is the clock provided by the computer for reading the RAMs (is applied to ICzob). The INH signal prevents triggering of the circuit via bistable FF: until the RAM has been read completely by the computer. The computer uses the C/I signal to determine whether the RAM is being written to by the drive unit, or is being read by the computer (logic 0 = reading). A logic 1 on the EXT line actuates the external trigger input. Lines OF« to OF. carry the off-set voltage that is added to the input signal via the D-A converter. The standard value should be 1000000 or 0FFFFFF to give an off-set voltage of 1 V (OF. = MSB). A logic 1 on the AC-DC line causes relay Re > to be energized, so that ca- pacitor Ci is short-circuited and DC components in the input signal are passed on. The data on the T« to T. lines deter- mines the trigger level. To enable triggering at the zero crossing of a signal, the value should be set to exactly half the signal level, that is, 1000000 because of the standard off- set of 1 V (T. = MSB). The + /— line enables the computer to choose between triggering at a signal that exceeds the trigger level either in a positive or in a negative The READY signal indicates to the computer that writing into the RAM has been completed and that the reading process can begin. The in- ternal clock signal is switched off at that instant. Lines TBs to TBj servo to choose the required time base via ICs A value of 0000 corresponds to 1 mV/div, and 1111 corresponds to 100 mV/div (TBj = MSB). Lines Vs to Vi are used for setting the input sensitivity via the lultiplexers in the attenautor stages. A value of 0000 gives a sensitivity of 10 mV/div, while 1010 gives a sensi- tivity of 5 V/div. Data lines Di to D; incl. are used for transporting the binary values from the drive unit to the computer (D?» = MSB). Line D7b carries the trigger bit. This information makes it possible to writer suitable program for the com- puterscope. In many cases that will not be necessary, however, because a complete program listing for the BBC, the Electron, the Commodore C64, and, very likely, MSX com- puters will be supplied with the printed-circuit board. More about this in Part 2 next month. AIR DEFENCE SYSTEMS FOR COUNTRIES AND CONTINENTS by John Nicholis, CEng, MIERE' Air provides the breoth of human life, and the space it occupies around the globe has become the dominant "play volume" in man's defence of his kingdom. The armed forces meet varying threats. The primary con- cern ot navies is high and low flying attack weapons, armies have to contend with strike aircraft and missiles, while air forces are required to intercept bombers and fighters and eliminate all threats that exist in the air space. To maintain vigilance in times of peace and to meet the threats of in- surgents in times of war it is vital that all the resources of the armed forces are co-ordinated. Co-ordination is important not only for the air battle but for the safe operation of civil aircraft, and re- quires close co-operation between the defence organizations and civil aviation authorities. An air defence system pro- vides this co-ordination. It is able to detect, recog- nize, and monitor infor- mation on objects in the air space. It can provide the command and control of interceptor aircraft, the dissemination of target in- formation to field batteries of guns and missiles, and it can provide the com- mand with a display of a recognized air picture and sometimes of the sur- face as well. This includes all information necessary for decisions to be made. Modular advantages Traditionally, only highly industrialized countries have been able to benefit from large scale air defence systems. Each system would be custom designed resulting in ex- pensive and specialized solutions. Analysis has shown that common func- tions exist in all the elements of air defence sysiems around the world and it is this that, for in- stance. Plessey Radar has capitalized on with its air space management prod- ucts. The result is a base ot hardware and software models, which include off- and on-line maintenance aids able to be con- figured at low cost into vir- tually any size or variety of air defence system by the addition of customer specific facilities. The modular design ap- proach has additional ad- vantages. Rigorous speci- fications and method- ologies can be applied and the modules sub- lected to thorough In- service use. It also makes the transfer of technology more amenable and simplifies local mainten- ance. Plessey Radar already has a number of such systems installed and an oper- ational development and demonstration air defence facility at its systems head- quarters. It is now feasible for any nation to have an air defence system that precisely meets its needs and is affordable — both initially and throughout the life of the system. The next few years should see a large number being in- stalled and integrated on an international scale. The air picture The first requirement of an air defence system is to detect the targets. This can be done passively with electronic sensor measurement (ESM) equip- ment to detect audio, radio frequency, and in- frared emission. It can also be done with active sensors such as radar and laser equipment and, of course, that original sensor, the eye to report visual sightings. All the in- formation from these sen- sors, whether they be static or mobile, on the land, at sea, or in the air, is processed by reporting posts. The data provided by reporting posts range from crude directional bearings to accurate recognition of the targets along with positional co- ordinates. From the reporting posts, the data are transmitted tor processing at a control report post. Here, the data are combined with known information, such as civil aircraft flight plans and In- formation from secondary surveillance radar, to pro- vide a track database whose accuracy and completeness determines the quality of the air defence system. Operators at display con- soles in the control repor- ting post use this track information to select their targets, to control fighter aircraft on their intercep- tion missions using air- ground-air radios, or to provide targeting infor- mation to SAM (surface-to- rn 1986 1 1 -23 air missiles) and gun weapon sites. The information is also fed to an air operations centre where again it is combined with inputs from other control reporting posts, processed with multi-sensor algorithms, and displayed as a rec- ognized air picture for the whole play area covered by the sensors with each target having a unique track identity. Defensive network At the air operations centre, other information is also shown on consoles and large screen displays to enable the command to plan the tactical and strategic air battle. Details of the status and avail- ability of aircraft, guns, and missiles are available along with mission desig- nations and the logistic situation from national and allied forces. The remaining task of the air defence system is to pass the recognized air picture to a central joint operations centre. Here, a totally integrated view can be obtained by com- bining the information from the air operations centre or centres with similar inputs from navy and army systems to give a complete recognized air and surface picture of the country's defensive network. The command and control aspects of an air defence system will vary, depend- ing on factors such as the size of the country, the volume of air space to be defended, and the existing defence manage- ment organization. There are three fundamental methods of meeting the requirements. First, command and con- trol can be centralized. Activities undertaken by the control reporting post and the air oper- ations centre will nor- mally be centralized into one facility, often in a single building. For small countries with, say, six sen- sors giving coverage of up to 930 x 930 kilometres, this is a suitable air defence system architec- ture. Control options Command and control structures can be kept relatively simple and the number of expert staff re- quired can be limited. The track database targets that can be effectively monitored — would typically contain up to 300 tracks and controllers could handle up to ten "close" and 20 "loose" in- terceptions. Second, where air space management demands a significant number of sen- sors (more than six) and the defence assets such as guns and aircraft are distributed over large areas, a system with cen- tralized command but decentralized control can be used. Groups of two or three reporting posts pass data to tactical command reporting posts which are normally termed sector operations centres when more than one sensor is connected. These in turn transmit their information to the air operations centre. This is the most common form of air defence system. The dispersed sensors and mobile command repor- ting posts concept is resilient to damage and the command organiz- ation is relatively easy to implement. Typically, each sector operations centre - the decen- tralized control — can handle 200 tracks and 30 control interceptors while the air operations centre — the centralized com- mand — would have a track capacity ot over 500 after combining all the in- puts from the sectors. The third method is to distribute command and control responsibility to centres that exercise total authority in specified areas. Each then reports to a centralized strategic command function. This air defence architecture meets the needs when several states are involved or when a large continen- tal area has to be de- fended. It is an extremely complex task to define the hierarchy of command, to identify and allow for overlaps of data, and to distribute this information around the regions. It re- quires close co-operation between participating states. international integration As well as accom- modating the many vari- ants of command and I control, an air defence system design must allow for future expansion, not only within the country but also for integration with in- ternational air defence facilities. The data processing system is the key to this versatility. A well-designed system will have modules of hardware and software that can be integrated in various forms depending on the requirements. It must at the same time be tolerant to failure and able to accommodate dif- ferent computer types and software languages that are likely to be introduced as the system expands I and equipment becomes obsolescent, j The ideal architecture consists ot distributed ] nodes of processing that are expandable in power. These are coupled via local area network (LAN) open system interconnec- tion (OSI) standard data communications. Com- puters with applications software can be added to the local area network with no major impact on the logic system. Avail- ability can also be en- sured by building-in spare computers coupled with automatic fault detection and techniques that en- sure graceful degrada- The hardware must be capable of installation in mobile cabins that can be transported by land, sea, or air, as well as in static facilities. Software, likewise, must be capable of being maintained and amended on site to handle local environmen- tal data. Compatible techniques Most countries have many sensors, rarely from the same supplier. The other command and control systems with which the air defence network must in- terface are also likely to be different. It is, therefore, unlikely that the data to be exchanged are of similar format. The air defence system must use techniques that ensure compatibility at all levels from the reporting post up to the air oper- ations centre while minimizing any impact on the central air defence data handling systems and the other systems with which it is interfaced. The distributed logic system architecture can readily accommodate the special normalizing pro- cessors needed to over- come these problems and they can be interfaced to the local area network by the appropriate open system interconnection communications. (LPS) ■ John Nicholls is an Engineering Executive with Plessey Radar Systems • Oakcrott Road • Chessington • Surrey KT9 1QZ. Voltage comparison on a scope There is frequently a need, when exper- imenting with circuits, to measure or compare several DC voltages at test points etc. Since most readers are un- likely to possess more than one multi- meter this can be rather tedious. Using this simple circuit, up to four voltages can be compared or measured on any oscilloscope that has a DC input and an external trigger socket. The circuit uses only three ICs, five resistors and a capacitor. The complete circuit of the voltage comparator is given in figure 1 . The four voltages to be measured are fed to the four inputs of a quad analogue switch IC, the outputs of which are linked and fed to the Y input of the ’scope. N1 to N3 and associated components form an astable multivibrator, which clocks counter IC3. This is a decade counter connected as a 0 to 3 counter by feed- back from output 4 to the reset input. Outputs 0 to 3 of the counter go high in turn, thus ‘closing’ each of the analogue switches in turn and feeding the input voltages to the 'scope in sequence. Output 0 of the counter feeds a trigger pulse to the ’scope once every four clock pulses, so that for every cycle of the counter the ’scope trace makes one sweep of the screen. A positive-going This simple circuit allows up to four DC voltages to be measured or compared by displaying them side by side on an oscilloscope. (H. Spenn) trigger pulse is available via R4, or a negative-going trigger pulse is available from the output of N4 via R5. The resulting display is shown in figure 2, four different input voltages being fed to the inputs in this case. The oscillo- scope timebase speed should be adjusted so that the display of the four voltage levels just occupies the whole screen The supply voltage +Ub may be from 3 to 15 V, but it must be noted that the input voltage should be positive with respect to the 0 V rail and not greater than +Ub- If voltages greater than this are to be measured then potential dividers must be used on the four inputs. Setting up To calibrate the circuit, simply feed a known voltage into one input and adjust the Y sensitivity of the ’scope to give a convenient deflection (for example one graticule division per volt input). The unknown voltages may then be fed in and compared against each other and against the calibration. The circuit can easily be extended to eight inputs by adding an extra 4066 IC and connecting IC3 as a 0 to 7 counter (reset connected to output 8, pin 9). k Figure 2. An example ot 4 random voltage INDOOR UNIT FOR SATELLITE TV RECEPTION-1 by J & R v Terborgh Following last month’s general introduction to satellite TV reception, this article describes the construction and operation of the indoor unit (IDU). This is in essence an interface between the low-noise converter (LNB) at the dish aerial and a conventional television receiver. The first part of the article deals with the RF board contained in the IDU. Indoor converter for satellite TV I I • Single conversion, wideband FM tuner • Complies with standard LNB IF range 1950 1750 MHr) and downlead feed systems (or CS and future DB satellites 111. • Includes VHF vision & sound remodulator. LNB theft alarm, polarisation selector, audio and video outputs, and switchable AFC. * • Remodulator test and satellite scan circuits simplify initial setting up and dish positioning. * • Also usable as a 23 cm band 11240 .1280 MHsI amateur television (ATV) receiver. " To be detailed in a forthcoming article. Before embarking on this project, make absolutely certain that a 1.2 m and 1.8 m dish aerial can be securely installed to give an unobstructed line-of-sight path to the relevant satellite^). As stated last month, it ap- pears that garden installations are all right, but roof installations require planning permission. Careful plan- ning and expert counsel in this mat- ter will prevent costly and frustrating disappointment at a later stage. It should be noted that at present it is virtually impossible for most home [ constructors to build either the dish | aerial or the low-noise converter, and I these will, therefore, have to be bought or rented. In this context, see Satellite TV reception (p.40) and Har- rison Electronics’ advertisement (p.86) in the September 1986 issue of Eiektor Electronics. Fortunately, prices of these units have already started to come down due to the rap- idly growing interest in satellite TV reception. Although the construction of the in- door unit is not recommended to ab- solute beginners in electronics, it should be noted that a number of prototypes were built by construe- , tors with only limited experience. In the main, the results were fully satisfactory, although all agreed that their task had taxed them to the full, requiring not only great precision and care in soldering, but above all close attention to the constructional details. The present article, there- fore, aims at giving the maximum clarity to all matters concerning very- high-frequency techniques. For an explanation of parameters and abbreviations used in this article see j Satellite TV reception in the September issue of Eiektor Elec- J ironies. have an output of 9SO-1750 MHz IF amplifiers Ti ICi, and Ti inter coupled by band-pass filters, pro vide a gain of about 42 dB at the half-power bandwidth (>36 MHz). A phase-locked loop (PLL) demodu lates the 610 MHz IF signal an passes the baseband (about 0-8.5 MHz) to the video processing circuits (de scribed in next month's issue) via buffer T*. The relatively high IF of 610 MHz en- sures good rejection of the 2170-2970 MHz image frequencies, t (fi=fio+fir). Circuit description In the circuit diagram of Fig. 2, the SHF input stage, Tt a Type BFG65 transistor, has been designed for low-noise (FaB=4.5 dB max) wide- band operation. It presents a 50-ohm impedance to both the input from the LNB and to mixer MXi. Its gain ranges from about 12 dB at 950 MHz to around 8 dB at 1750 MHz. MX. is a Type HPFS11 monolithic wideband, double-balanced mixer (DBM) consisting of four Schottky 1 diodes, which have a low junction capacitance and provide linear op- eration over a wide range of LO and RF power levels. These diodes are noise ratio to be less impaired in the mixing process. The characteristic curves in Fig. 4 ( show some of the parameters of the I HPF511. In particular, Fig. 4c shows the excellent performance of the device at a local oscillator power ! level of +7 dBm (about 5 mW). Since j the input impedance. Z, at pin 8 is 50 ohms, the output voltage, Ulo, of the local oscillator is given by Uio= \PloZ, = ( 0.00S x 50 = 0.5 V,™. Readers interested in balanced RF mixers should find the RF/IF Signal Processing Handbook, Volume 1 (Literature reference [2]) well worth reading. Local oscillators Ts and Ts' cover the 1560-2360 MHz band at sufficient power for satisfactory operation of the mixer, and have the stability re- quired for wideband FM TV recep- tion. Since it proved virtually impossible to achieve this perform- ance with a single transistor, two varactor-tuned Type BFW92 tran- sistors are used. The two sections of the oscillator, LOl, and LOh, are tuned to the highest and lowest channels of satellite TV services re- spectively by C* and Cx'. Section LOl covers a range of about 1500-2000 MHz, and LOh operates over roughly 1800-2400 MHz. The Fig. 1. Block schematic diagram of the RF board in the IDU. Note that two local oscil- lators. LOi, and LOh. have been incorporated to supply the 1560- 2360 MHz injec- tion signal. fed via high-quality transformers to j stability of the oscillators is so good Block diaaram give a meticulously balanced set up j that automatic frequency control | ' = ’ suitable for operation at high RF. LO, (AFC) is not, strictly speaking, re- The block diagram in Fig. 1 shows and IF frequencies. The internal or- quired. that the indoor unit is a single- ganization of the device is shown in The relevant oscillator section is conversion superheterodyne tuner. | Fig. 3a. selected with S., Resistors Rro and A low-noise amplifier raises the level The Type HPF511 was chosen be- R? 1 in LOl and R20 and R;> in LOh of the 950-1750 MHz input from the cause of its robusmess, excellent t are damping resistors, which pro- LNB, which is then mixed with the performance-to-price ratio, and | vide enough inductance to ensure 1560-2360 MHz output of local stable impedance at all three ports, I correct matching to the 50-ohm LO oscillators Ts and Ts’. which are designed to handle a wide 1 input of mixer MX. It should be noted that LNBs used for range of RF input signal levels. Its ! The common 3-32 V tuning voltage, the reception of communication sat- drawbacks are its cost as compared [ Vt .n. , is applied to varactors Di-D. ellite TV programmes use a 10 GHz with a discretely built mixer, and its (LOl) and DrD/ (LOh) via resistors local oscillator to give an output of conversion loss. However, an active R-s and R.V respectively. 10.95-11.75 GHz. Fortunately, the mixer, which would have some con- | The oscillator stages operate in the European Broadcasting Union (EBU) version gaia is difficult to keep 1 common collector mode: oscillation has recommended (Literature refer- stable over the RF input range of is achieved through positive feed- ence [1]) that LNBs for direct broad- 950-1750 MHz. Moreover, the passive j back via the base-emitter capaci- casting satellite (DBS) services also DBM typically causes the carrier-to- 1 tance of the transistors. .1 1 -27 The 610 MHz IF signal is taken from pin 3 of MXi and capacitively fed to a conventional amplifier, T2, which provides about 10 dB gain at a rela- tively low noise figure; it also en- sures correct termination of the IF output of MXt. The first IF band-pass filter consists j of two critically to slightly over- critically coupled tuned line indue- j tors, I» and Lj. Correctly aligned, ! these have a 3 dB pass band of about ; 40 MHz, a relatively low insertion loss, and cause minimal stray radi- j ation. Both the collector of T2 and the j input of ICi are capacitively coupled to a low-impedance matching tap on | the relevant inductor. Second IF amplifier ICi is a wide- band hybrid IC Type OM361, which is primarily designed for VHF/UHF | masthead aerial amplifiers and j MATV systems. This single-in-line ( (S1L) device contains a 3-stage RF | amplifier as shown in Fig. 3b. The OM361 was chosen for its high gain (about 28 dB at 600 MHz) and ease of input/output matching. Power to the final two cascaded transistors is sup- plied via choke Ls to prevent the RF signal from being short-circuited by the thoroughly decoupled positive supply rail. Band-pass filter Ls-L; and amplifier T3 have functions and characteristics similar to those of L3-L4 and T2 re- | spectively. The IF signal at the col- j lector of T3 is capacitively fed to 1 phase-locked loop (PLL) decoder IC2. It must be stressed that the overall I performance of the IDU depends to | a large extent on the bandwidth, I rather than the gam, of the IF chain. Since the deviation of the satellite TV signal is typically + 13.5 MHzpp, and the baseband occupies some 8 MHz, the IF bandwidth must be not less than 36 MHz for satisfactory per- formance. It is, therefore, clear that the IF band- ! pass filters are crucial to the cor- j rect operation of the IDU. Since the j combined gain of the IF amplifiers j amounts to 48 dB, and that of the IF i chain is about 42 dB, it follows that the total insertion loss of the filters is j around 6 dB Next month's article will contain measurement data relevant to the RF j sections of the IDU. PLL decoder IC2 is a purpose-de- | signed satellite TV FM demodulator j Type SL1451 from Plessey and is part of an extensive range of passive and active components intended for sat- ellite reception systems (Literature reference (3J). The functional diagram of the device is shown in Fig. 3c; inset is the on- chip voltage-controlled (Clapp) os- cillator (VCO). The Clapp oscillator generates the I also serves as an RF block reactance. 610 Mhz sub-carrier for demodu- j Both outputs, pins 15 and 14 respect- lating the IF signal. It is tuned exter- j ively, are fed back to the relevant in- nally by line inductor Ls, varactor Da put pins 16 and 1 respectively by and trimmer Ca, and coupled to one means of capacitors, which define of the (differential) inputs (pin 6) of i the secondary loop filter response; the phase detector via C30. The other | the values of C?o and C21 may be input of the detector, pin 7, is de- altered to suit the deviation of the re- coupled by C;s The output power of ceived signal; this will be reverted to the oscillator is stated to be— 10 dBm, in a forthcoming continuation of this j which is claimed to be the optimum ] article. The stated values of these figure for threshold performance components ensure a PLL noise (Literature reference |4|). | threshold of about 10 dB C/N at devi- Varactor Ds provides a frequency-to ations of 13.5 MHzpp to 20 MHzpp. voltage gradient of about 14 MHz per | Careful redimensioning of the sec- volt: at the most commonly used de- ondary loop arrangement may lower viation of 13.5 MHz PP , therefore, the j the PLL threshold to 8.5 dB C/N; this baseband output swing is about | is not at all easy, however, and the 1 Vpp (note, however, that some 1 matter will be taken up for examin- j transponders are run at higher devi ation in due course. Around the ] ation values). threshold level, the PLL produces | The RF amplifier in the PLL chip 1? a sparklies or spikes on the picture differential type with one input (pin screen. This effect, however, dissap- 12) decoupled, which results in an in- pears as soon as the C/N figure put handling range of —25 dBm to rises some 2.5 dB above the PLL 0 dBm. threshold. Both video and inverted video are The automatic gain control (AGC) output: the former is fed to D 1 via j output of the SL1451 is used to drive j primary feedback loop L9-R11, which a relative signal-strength (S-) meter | fig. 2. Circuit diagram of the RF board in the IDU. As customary in RF circuit drawing, ground connec- tions have been shown as they are effected in actual construc- tion practice. Dashed lines denote screens fitted onto the board to prelude parasitic coup- ling of tuned cir- cuits. Also note that tuned line inductors are shown as shaded blocks; coupling is inductive. Fig. 3. The inter- nal configura- tions of the centra! building blocks of the IDU RF board: (a) wideband double-balanced mixer Type HPF511; (b) hybrid VHF/UHF amplifier chip Type 01436 1, and (c) FM-TV PLL detector Type SL1451, featuring an on- chip 400-800 MHz Clapp oscillator. 1-29 Fig. 4. Graphs correlating a number of im- portant techni- cal character- istics of double- balanced mixer MXi. Remember that RF - 9 SO . . 1750MHz. IF = 610 MHz and LO = 1500. . 2400 MHz at +5 to + 7 dBm, which is obviously the correct level for lowest conver- sion loss and highest port-lo- port isolation. Fig. 5. Before fit- ting any parts onto the board, it is necessary to finish all drilling and filing of the metal enclosure sized 100xl60x 30 mm (WxLxH) incl. of top and bottom lids. Fig. 5d shows the home-made version of feed- through Cm. 5 a J r * — 11 — ¥ 1 circuit via pin 9. Buffer T« is a simple emitter follower that serves to output the baseband at low impedance. Note that its output is direct-coupled, since the DC com- ponent is required for use in the I AFC and video processing circuits. It is important that feedthrough ca- pacitor C« has a capacitance of not more than about 30 pF to prevent it filtering or limiting the baseband. The supply voltage to the PLL chip is stabilized at 8.2 V by zener diode D> , and is also decoupled at several points to prevent oscillator instability and signal loss. The dashed lines in Fig. 2 denote metal screens on the printed-circuit ! board: these provide effective pro- tection against stray inductive coup- | ling of tuned circuits and parasitic I oscillations. j Finally, all DC connections to the RF | board are decoupled by 1 nF feed- through capacitors. j Construction Contrary to the normal order in which electronic projects are put together, it is necessary to finish all mechanical work as detailed below, before fitting any parts onto ready- made PCB Type 86082-1. First, prepare a 160 x 100x28 mm (in- side) brass or tin sheet enclosure as shown in Fig. 5. If you can not obtain a preformed enclosure, you will need to cut four suitably sized pieces of 1. . .2 mm thick brass, drill two of these as shown in Fig. 5a and 5b, and join them to form a neat box using Sellotape at the corners to maintain right angles as you solder, using a heavy-duty (5100 W) iron, j Brazing is, naturally, even better. Check whether the eight feed- through capacitors and BNC flange socket Ki fit snugly into the holes; if not, carefully ream the holes until they do. Do not solder anything as yet. File a notch into the PCB to allow for the PTFE ring round the centre pin of Kt. Check whether the PCB needs any filing off the sides before it can be received into the box. Fit Ki by its four small screws, but do not secure these as yet. Pre-tin the holes provided for the feedthroughs, and insert these from the outer side of the enclosure. Point them downward as you apply heat and solder; if all goes well, the capacitors should slide snugly into j place while hot solder runs smoothly round the conical metal bodies. While soldering, carefully ma- noeuvre the capacitor into its final position. Since low capacitance (10 . . . 27 pF) feedthrough capacitors are difficult 11-30. to obtain items, it may be necessary to make a DIY version from a number of parts intended for the isolating of power semiconductors on heatsinks. Fig. Sd shows how a small washer, bush, two soldering tags and a bolt i plus nut can be put together to act as [ a low-capacitance feedthough. It is i definitely less elegant than a real ca- pacitor, but it works satisfactorily and has capacitance of about 50 pF j The PCB for this part of the project is I a pre-tinned. double-sided type, | equipped with 5 mm holes for Ti to ! Tj incl. and slots for Cm and Cm', j Through-plating is effected by j soldering component leads at both : PCB sides, where required. Start off by applying some solder | onto all ground holes on the PCB, as well as onto its edges at both sides; j this will facilitate soldering at a later j stage, and prevents overheating of J grounded components when these | are fitted. Make sure, however, that j holes remain open (use solder wick). Resistors: with a few exceptions in j the LO sections of the circuit, these j should have their leads neatly bent 1 equidistant from the body with 1 snipe-nose pliers. Pre-tin any resistor j lead that is to be inserted into a j ground hole. All resistors should be j b or Vt watt (except Ru, which is i Zi W) carbon film types; not metal ! film. Resistors should be fitted to rest ] securely on the PCB component side. Capacitors: In the case of a supply decoupling capacitor (InF, 10 nF, 22 nF, 4«7 and 10 p), pre-tin the ground lead close to the capacitor body. With some types of 2.5 mm type ceramic capacitors, it may be necessary to carefully remove some of the brittle material on the wire where it leaves the capacitor body; pre-tin as fast as possible, holding the far end of the lead in pliers. When soldering the ground terminal at the PCB component side, solder can be observed to creep right up to the ceramic body, and spread smoothly over the ground plane. Coupling capacitors do not require this method of pre-turning, although they should be mounted with the shortest possible lead length as well. Trimmers are to be pushed securely into the relevant holes and soldered rapidly to prevent deforming of the foil material. Transistors; with the exception of the BFW92s and the BC547B, b and c leads should be cut off to about 2 mm, e leads to 3-4 mm. Before fit- ting, note the terminal assignment of the BFG65 to get its position correct. Transistors Tz and Ti should be mounted at the EPS side of the PCB, straight onto the relevant tracks and with the type lettering visible from overlay and track pattern shown in ; plane. Fit Ti in its pre-drilied hole, Fig. 6, and observing the foregoing soldering the b and c leads direct directions, the fining of parts onto onto the relevant tracks, the e leads the PCB may now commence. firmly to ground. Solder SMD capaci- RF amplifier T and mixer (see also ! tors C- and Ct with a light-duty Fig. 9). (15 W) iron to prevent damaging Fit all passive parts as set out above these devices. Alternatively, Ci and Pay special attention to LNB block in C> may be 6p8 ceramic types ductor Li. which is fitted slightly oft mounted onto the relevant planes the board surface, and has one end with the absolute minimum of lead soldered direct onto the RF input length (£0.5 mm). Lz and R. must be Table 1 Inducin' SWG internal diameter remaik(s) 24 enam 3 mm dose wound. 24 enam through 3 mm ferrite bead. L>;1* 20 silv. tuned line; length and location of tap governed by relevant PCB holes fit 3 mm above ground. 20 silv. .is above but no tap. dosewound on Ru. Lio;Lio* 1% spacing 1 V, mm initially; see Fig. 8c L.,:L„- resistor lead tuned line; see Fig. 8c. -31 Fig. 6. Compo- nent overlay and track pattern of the /DUFF board. Note that the local oscil- lators incor- porate com- ponents not fitted onto the board in the usual way. Not shown are feedthrough capacitors Car to Cm incl. which are fitted into the lower side panel of the enclosure. Fig. 7. Neatly made inductors are the key to satisfactory per formance of the IDURF board. Showing a number of parts, ready for mount- ing onto the PCS. Left to right, top row: PLL loop in- ductor La wound on Rn, La on a small ferrite bead, a 1 nF feedthrough ca- pacitor, and trapezoidal chip capacitors Cm and Cm '. Second row: +LNB block coil Lt, silver-plated strip lines L3 and soldered as close as possible to the transistor body (b and c terminals re- spectively); note that Ri may have to be mounted slightly asymmetrically to ensure minimal stray inductance at the transistor base. MX 1 is located at the EPS side of the PCB, while its eight pins are soldered at the component side. Note that the RF input (pin 1) is marked in blue for location pur poses. IF amplifier. Solder the MXi connection of C7 at both PCB sides, but that to the base of Tj at the EPS side only. Tuned lines La. La, U and L7 are best fitted as follows (see also Fig. 8b). In- sert a left over component wire into the PCB holes provided for the taps, and solder at the EPS side Use the protruding pin at the far end of the vernier gauge handle to determine a wire length of 3 mm above the com- ponent side ground plane; cut the wire and level its top with a few strokes of a small file, while the wire is held securely in pliers. Pre-tin the top and position the wire at right j angles to the PCB. Mount the sil- vered line, pushing it into place until it rests on the tap wire end. Make sure that the inductor is precisely | angled and that its horizontal part is ( always exactly 3 mm above ground, j Solder the trimmer and double j ground connections, and then the tap. Remember that any excess solder on its silver plated surface may degrade the inductor's O-factor. Make sure that the coupled lines run parallel and at identical height above ground. After inserting the pins of the OM361 until all studs rest on the PCB sur- face, they must be soldered rapidly (five pins twice to ground), after which the SIL chip must be bent downward with its tyoe indication facing the PCB component side ground plane Do not use too much force, or one or more of the pins may come break off. Fitting the remainder of the IF ampli- fier components should not cause difficulty, as the suggested methods for mounting have already been de- tailed above. PLL and baseband output. Mount IC» without an IC socket, and remember to solder pins 2 and 8 at both PCB sides. The surrounding capacitors and resistors should be fitted as set out, while block inductor Ru-Ls must be mounted at a small distance above the board (1 mm) to prevent any likelihood of a short- circuit. Tuned line Ls is fitted at pre- cisely 3 mm above ground. Mount varactor D2 with the minimum of lead length at either side of its glass body. Make sure that it is really a BB405G; -32 elektofin it should have a green and a white ring, the latter indicating the cathode connection. Local oscillators (see also Figs. 8c and 9). You are now well on the way towards completing the RF board, but the toughest part is yet to come: no PCB holes in many cases, and a few parts mounted three-dimensionally; and yet, it is not as difficult as it may seem at first. Note that all part references in the following description also apply to the corresponding accented (') parts, unless a specific description is thought necessary to make a distinc- Fit decoupling and bias parts Ris, R.t, Ri’, Cs j, Cm and Cm as set out above. Pay due attention to the fitting of Ts , as it has neither a hole nor any tracks to connect to other compo- nents. As illustrated in Fig. 8a, the transistor’s collector lead is to be I sharply bent where it leaves the | enclosure. Push-fit the lead into the | slot, along with chip capacitor Cj*. until the latter's shoulders rest firmly on the PCB surface. Gently ma- noeuvre the decoupling capacitor and tap the transistor until this is felt to lie level onto the PCB surface. Note that emitter leads of Ts and Ts ' should face one another, requiring junction Rm-Rw) to be rather longer Ts unlike Ts'.tolie with its type indi ( than usual, but this is of no conse- | cation facing the PCB ground plane quence. Sharply bend the anode | Carefully solder the track and | lead of varactor D<, pre-tin, and I double ground connections of the J solder to ground (2 x) using the hole I chip capacitor, and make sure that provided. Note that the ground con- I solder creeps up along the metal- j nection of D<’. (LOh) is closer to Ts lized area and the collector lead, ' than that of D< to Ts (LOl). Shorten whose excess length is then cut off | the D* cathode lead to 2 mm, pre-tin. Shorten the transistor's e and b leads and do the same with Di . Carefully to 2 mm and pre-tin them Fit stopper join these parts and run the ap- resistor Rn with the shortest poss- j propriate length of the D3 anode ible lead length (<1 mm) as close as ! wire to junction Ru-Ts. Since junc- possible to the transistor body (b); tion Ris-Dj-D* should exhibit the ab- this may require the other lead (to I solute minimum of stray capacitance U Third row VCO inductor it I me (SWC TO silvered wire or /Kr wire may do used without any perceptible dif fetence in PLL operation). L» and L> Bottom row LO: and LOu inductors bio. L>o L« and in' are simply made from the leads of Rio and Rio ’, which should have a body length of 7.5 mm as shown. Note the differ- ence in position of L w' (left) and Lm (right) as seen from the as- sociated resistors. Bottom right is the type of ceramic ca- pacitor used throughout the I circuit ; use miniature 2.5 mm lead spacing types only Fig. 8. Artist's impression of suggested com- ponent mounting methods. Fig. 8a shows how the Ts and Ts ’ collec- tor leads, along with chip capaci- tors Cn and Cu '. are push-fitted into 6x I mm slots in the PCB. Fig. 8b shows that very little can go wrong if the tuned I me inductors are neatly bent to suit the relevant PCB holes. Fig. 8c, finally, should be used as a guide in constructing the " three-dimen- sional " local oscillators. Stick to these guidelines and your IDU RF board will work! il 1 -33 Fig. 9. Close-up view of LO and input/mixer sec- tions on a proto- type of the R F board in the IDU. If in doubt about some con- fully screen this fully fur. The small b. SMD capaciti inductance varactor-resistoi junctions in the LO sections. and inductance, R.s needs to be prepared as follows. At one side of I the resistor body, the protective lacquer should be scratched off where the wire leaves the body. This is conveniently done by holding the [ relevant area in pliers and twisting the resistor until the brittle stuff comes off. Shorten the lead to I O.S mm, pre-tin, and join it to junction Dj-D< with a minimum of solder. Note that the other lead of R, 9 ' (and of R19) must be left much longer, so that it can reach junction Ria-R^C; Since these resistors act as current limiters and chokes to the SHF signal on the varactors, this length is of little importance. Inductors L.o and Ln are made from the terminal leads of R». One lead is wound as \'h turns on a 3 mm former, which may be nail, screwdriver shaft, or even a ball-point refill, as long as it has a diameter of 3 mm. Leaving the turns to revolve around the former, the resistor is gently pulled 1 back until the lead length between I resistor body and start of winding I matches that given in Figs. 7 and 8c. I Space the turns as shown. I The other resistor lead is to act as L> Observe its length, and edge the re- mainder of the wire two times as J shown in the illustrations. Put the I prepared resistor & inductors aside for the moment, and proceed with the most exotic, yet simplest, part of the board: Cx, which is simply some 10 mm of left-over component wire, 2 mm of which is slightly bent, soldered to the Ts e lead, and pointed towards C36. The wire should not touch ground, of course. Solder L10 to junction Cx-Ts(e); this requires some skill to prevent short- circuiting the inductor turns by either Cx or the Ts emitter lead. Check for any short-circuits caused by excess solder, and carefully bend Cx to point to the body of Cs& The oscillators will not operate correctly if Cx is left out. Run R20-L1. exactly parallel to Dj-D- and solder Ln to ground, straight onto the PCB surface. Note that no ground hole has been provided; use ( the relevant illustrations and the component overlay to find the cor- rect iocation, level with MX. pins 7 and 8. Rio should now be positioned well above all other components. I Solder Ri. very close to Rio and run the other end direct to mixer pin 8. As R,. ' should have exactly the same total length as its LOl counterpart, the Lic'-Rn'-Lii' line needs to be mounted slightly slanting with respect to the Dj : D«’ line. Ground Ln at the appropriate location, and check the outlook of the LO sections against Figs. 8c and 9. PCB Recheck all soldering joints at both sides of the PCB, and remove any stray bits of wire or solder. With a sharp appliance and a cotton bud dipped in 95% alcohol, remove all excess solder flux, visible as brownish maner, from etched sur- faces in the RF input and mixer stage; do the same at the PLL sec- tion. If you have so far followed the instructions, terminal holes 1-8 incl. should still be open. Enclosure. j Fix K. securely by its four screws, whose heads should be at the inside | of the enclosure. File off any pro- truding thread until it is flush with j I the socket flange. Insert the completed board into the enclosure making sure that the centre pin of the BNC socket rests on the RF input plane (Li-C.); file or cut off any excess pin length. Refer to Fig. 5b for the positioning of the board and make sure that the bottom ltd can be pressed or screwed on without touching MX.. Use a heavy-duty iron (>50W) to solder the PCB into the enclosure; depending on the type of metal sheet, some pre heating may be called for to be able to solder at all. Use an additional soldering iron or place the enclosure on the hot sur- I face of a thermostatically-controlled smoothing iron; you will find that once the metal surfaces are reason- ably warm to the touch soldering becomes much easier. Mount eight soldering pins in the ter- minal holes if the wires of the feed- through capacitors are not long enough. Using the dotted lines on the PCB overlay as a guide, solder three 17 mm high metal screens onto the PCB component side (take care not to damage nearby parts). Note that the longest screen is to run right over IC2, so that a 20x4 mm recess hole should be made at the correct lo- cation. If you have made your own metal enclosure, do not forget the top and bottom lids, which are to be screwed on after the box has been fitted with at least eight square brass nuts, soldered into the upper corners. A few additional nuts and screws along the enclosure side panels are, of course, good practice to make for an RF-tight unit. Finally, drill the top lid as shown in Fig. 5c. Next time Part two of the article in next month’s issue will describe details of the vision and sound processing cir- cuits, the power supply, and the S- meter driver. Also, the alignment of the IDU will be gone into, and measurement data relating to its per- formance will be presented and dis- cussed. Bu Literature references: [1) Document D46: Choice of the first IF frequency range for DBS receivers. EBU Technical state- ment ref. EBU D46-1985 (E). \2]RF/IF signal processing hand- book, volume 1. Mini Circuits, New York. 13] Satellite Cable and TV integrated circit handbook. Plessey Semi- conductors. (4) Application note 56/SJ/00013 (SL1415). Plessey Semiconductors. Important notice Information on component avail- ability for this project will be given in Pan 2. to be published in next month's issue. Meanwhile, many pans are available from Bonex Limited; 102 Churchfield Road; Acton; London W3 6DH; telephone 01-992 7748; Universal Semiconduc- tor Devices; 17 Granville Court; Granville Road; Hornsey; London N4 4EP; telephone 01-438 9420; or Cirkit; Park Lane; Broxboume; Hens EN10 7NQ; telephone: (0992) 444111. 1 1 -34 elekto JOCKEYING FOR SUPREMACY IN EUROPE’S OWN SPACE RACE by Tim Furniss 'Jons Satellite Within the next ten years, the European Space Agency (ESA) will be operating an autonomous space station known as Columbus. It will comprise manned modules and laboratories, free-tlying platforms, and other equipment launched by the United States' Space Shuttle and the proposed European Ariane 5 rocket. It will be serviced by the European manned space- plane, Hermes, and poss- ibly by the British un- manned Hotol shuttle. As a member of ESA, the United Kingdom will play an important role in these projects, not only with Hotol, but also particularly the free-tlying platforms for Earth observation, astron- omy, and materials pro- cessing. Britain's financial contribution to ESA is 12.9 per cent and its partici- pation in mandatory ESA programmes represents 16 per cent of the effort and manpower. There is a thriving space industry in the United Kingdom and this has been involved in the building and operation of over 50 satellites, 2000 sounding rockets, and over 100 ground stations. Unlike that of many European countries, British influence in space tech- nology and commerce spreads beyond the conti- nent itself, and especially to the United States of America. British Aerospace (BAe) 111 is the largest manufacturer of communications satellites outside the United States and is a major contractor to American companies on a number of key projects. Although BAe tends to be the most familiar, several other companies are also actively engaged in the space industry on a large scale. The European Communica More versatile These include GEC- Marconi 01 tor communi- cations payloads and ground equipment, while others involved are Ferran- ti 131 , Logica, Klystrons, Centronic, Thorn-EMI, Racal, Software Systems, BAJ Vickers, and IMI Sum- merfield. These manufac- ture and supply other ground equipment, microwave tubes, detec- tors, solid state devices, digital data recorders, software, gyro packages, and rocket motors. BAe pioneered the use of three-axis controlled com- munications satellites, wh.ch are more versatile and can be built on a much larger scale for the mu'fitude of developing applications, such as direct broadcast tele- vision, mobile and maritime communications, and business services. The company has devel- oped a stable ot com- munications satellite platforms: the European Communications Satellite (ECS), Eurostar, and Olym- pus. The ECS 2-Eutelsat series satellites being built by BAe have 12000 voice circuits, two television | channels, and two re- I peaters to handle busi- : ness traffic. They have a 1 kW capacity. Three military communi- cations satellites known as Skynet are being built, too. These are also based on fhe ECS "bus" and include a communications pay- load from GEC-Marconi comprising four super high frequency channels, two ultra high frequency channels for voice data and telex, and one extra high frequency ex- perimental uplink. Power generation is 1.25 kW. Aircraft phone calls Three Eurostar satellites are being built for the London-based inter- national maritime organiz- ation, Inmarsat, on a contract worth S100 million Producing 0.75 kW of power, the Inmarsat 2 satellites provide indepen- dent L band ship-to-shore and C band shore-to-ship communications, with 250 and 125 voice circuits re- spectively. Eventually, they will also provide aircraft communi- cations enabling passen- gers to take and make telephone calls on civil aircraft. The Eurostar satellites can generate as much as 2.3 kW of power but this is weak compared with the world's largest communi- cations satellite, Olympus, one model of which can generate 8 kW, enough fo power 12 direct broadcast television channels. The next British Aerospace satellite under develop- ment is called the Big Communicator. The con- cept envisages clusters of powerful communication satellites (comsats) sharing geostationary orbit, pro- viding television broad- cast and fixed and mobile communications services. Inter-satellite laser links will allow communications within and between clus- ters via gateway satellites. Three versions of the Big Communicator are planned, the largest be- ing for direct broadcast television. This would generate 15 kW from a 50 m long solar array and carry 16 high power tele- vision channels. BAe also has a contract to build equipment for Intelsat 6, the next generation of satellites for the inter- national telecommuni- cations organization. Spectacular data The company produced significant Spacelab hard- ware which flew on Space Shuttle missions dedicated to Europe, the United States, and West Germany in particular in 1983 to 85. Twenty of the Spacelab pallets have been de- livered to America's National Aeronautics and Space Administration (NASA). These are used as the essential mounting points for equipment in the Shuttle payload bay. The European spacecraft Giotto, which had its rendezvous with Halley's comet last March, return- ing spectacular data, was built in Britain with BAe as the main contractor. The S45 million contract is just one of a number ot key science and applications satellites operated or planned for Europe and to be built using British ex- pertise. These spocecraft include the Ulysses international solar polar spacecraft, the European Remote Sensing spacecraft (ERS 1), Exosat, International Ultraviolet Ex- plorer (IUE), Infrared Astronomical Satellite (IRAS), and the Geostation- ary Orbiting Satellite (GEOS 2). The solar panels that will generate electrical power for the giant Hubble space telescope, hope- fully to be launched by Shuttle later this year, were manufactured by BAe as a huge foldable array. The company expects to build a set of replacement panels under a $7 million contract. Britain is investing S58 million in joint science and industry programmes covering remote sensing, data acquisition, process- ing, dissemination, and forecast. The Royal Aircraft Establishment's National Remote Sensing Centre at Farnborough co-ordinates this activity. In the meteorological field, GEC-Marconi is developing Europe's first advanced microwave sounding unit to fly on a United States' National Oceanographic Adminis- tration Agency (NOAA) satellite in 1990. Britain is a world leader in satellite instrumentation for remote sensing spacecraft. Close relationships The British National Space Centre (BNSC). formed in 1985, will in future co- ordinate the country's burgeoning space in- dustry. Based in London with a small staff, it will for- mulate a national space policy to be presented to the Government in June '86. To be effective, it should cover the next 15 years. The BNSC will need to es- tablish close relationships with industry, including the non-aerospace sector, both in contractual devel- opment and exploitation, and commercial space operations. It needs to pro- vide a coherent voice on space matters, seeking comprehensive rather than a fractional ap- proach, and to consider its role in education and public policy. The centre's director- general is Dr Roy Gibson, who, as the European Space Agency’s own first director-general, helped establish it and develop Europe's prestige in space. It is expected that Britain's space budget under his control will be doubled over the next two years to about S300 million to reflect the increased im- portance the country places on space. Although the United Kingdom only plays a small part in the Ariane launcher programme — Avica, Badg. Ferranti, and Midland Bank's share | represents just 2.4 per cent — BAe has proposed a revolutionary launcher to beat them all, including the proposed Ariane 5. Hotol, an initially un- manned spaceplane, will be the world's first single stage-to-orbit (SSTO) sat- ellite launcher and the I first to take oft and land | like an airliner. It will cut by half the cost ot deploy- ing satellites into orbit. In- deed, the measure may be greater than that. BAe says it could place a five tonne payload into low Earth orbit at a fifth the cost of current vehicles. | Complemen- I tary or replacement The revolutionary engine for Hotol is designed by | Rolls-Royce and will be I dual-tunctioning. It | breathes outside air like ] an ordinary airliner and I mixes it with on-board sup- | plies of liquid hydrogen during the initial climb ! through the atmosphere. Hotol then switches to in- ternal fuel supplies of I liquid hydrogen and | liquid oxygen, once the air at altitude gets too thin to be usable. | It is expected to cost S520 000 million to ; develop, and whether it j goes ahead will depend j on whether it is accepted by Europe as a com- plementary vehicle to i Ariane 5 and Hermes, or | even as a replacement for Hermes which does not meet with universal ap- I proval within Europe. So far, only about $5 million has been forthcoming for a proof-of-concept study and Dr Gibson hopes to be able to present the Hotol case to ESA before the end of this summer. Although the French Hermes manned space- plane has more short-term support. Hotol is con- ceived as compatible with the United States' Space Station and its eventual European counterpart. It will also be manned for I some sorties. Ultimately. visionary engineers see | Hotol as the successor to Concorde, carrying a passenger pod in its payload bay on a journey between Londen and Sydney. Australia, in 67 minutes. t Enormous potential Like France; the Netherlands, West Germany, and Italy, Britain has a squad ot astronauts, or more correctly, Space Shuttle payload special- ists. Two of these are due to fly Shuttle later this year and early in 1987, primar- ily to help in the deploy- ment of Skynet 4A and 4B military communications satellites. They will begin British experiments into microgravity processing. The potential of this business is enormous and the BNSC is anxious to educate British industry as to its possibilities. Kodak Ltd, a subsidiary of Eastman Kodak in the United States, has already flown experiments on the Shuttle and a fluid physicist from the company may be joining a crew in 1987 to 88 to operate his own ex- periments. Clearly, commercial oper- ations are some way off, perhaps 20 years away, but vital research and development work needs to be done in space now. This is an area where Britain has been slow to move but it has the capability to catch up with France and West Germany, which are already forging ahead in this field. (LPS) ■ Tim Furniss is Associate Editor of Space Report 1 British Aerospace Dynamics Croup, Space and Communications Div- ision, Argyle Way, Stevenage, Hertfordshire, England, SCI 2DA. 2. GEC-Marconi Instru- ments Ltd, Long Acres, St Albans, Hertfordshire, England, AL4 OJN. 3. Ferranti PLC, Crewe Tbll, fbrry Road, Edinburgh, Scotland, EHI1 IPX. eleklor indie November 1986 1 1 -37 RF CIRCUIT DESIGN * The first three appeared in the March, April, and May issues of Eiektor The fourth in this series on RF circuit design * describes a superregenerative short-wave receiver that can be coupled to a frequency counter for an accurate read- out of the frequency of the received signal. superregenerative short-wave receiver A superregenerative receiver is provided with ample positive feed- back so as to be capable of oscil- lation at the desired radio frequency It is also provided with a means by which oscillations can be stopped or started at will. During normal oper- ation, the relevant circuit is just oscillating. Block diagram Fig. 1. Block diagram of the short-wave re- ceiver Table l. Winding data for Lt. From the block diagram in Fig. 1 it is seen that the RF signal intercepted 1 by the aerial is fed to an RF stage, which not only serves to amplify the signal but also to decouple the aerial from the remainder of the receiver. The amplified signal is fed to a buffer and a detector stage. The output of the buffer may be used to drive a fre- quency counter to give a read-out of the received frequency. The de- modulated output from the detector is passed through a low-pass filter 90 m 75 m 60 m 49 m 31 m 25 m 19 m 16 m 13 m L2A 132 99 82,5 66 54 45 34 27 21 18 14 12 12 9 7.5 The core is a Type T50-6 RF toroid available from Cirkit (telephone 0992 4441111 or Bone* (telephone 01-992 7748), while the winding wire is 0.3 mm dia. enamelled copper. with a cut-off frequency of 5 kHz and then applied to an AF amplifier. The audio output is sufficient to drive a pair of headphones, but may also be used to drive a more powerful AF amplifier. Circuit description With reference to the circuit diagram in Fig. 2, the aerial signal is applied across potentiometer Pi, which enables the signal to be set to the correct level, as will be ex- plained later. MOSFET Ti amplifies the input signal and decouples the aerial cir- cuit. The amplified signal is applied to a detector, the Gi-S junction of Tz, via circuit L;-C;-Cr-C«-Cio, which is tuned to the frequency of the incom- ing signal. Part of the RF signal is applied to the Gz-D junction of Tz from where it is fed back inductively to the tuned cir- cuit. As this feedback is positive, oscillations tend to be set up in the tuned circuit at the frequency of the received signal. These oscillations are quenched by the resistance of Pz . depending on its setting, so that this potentiometer affords a means of bringing the tuned circuit just into oscillation. The demodulated output at the source of T2 is applied to low-pass filter Lj-Cis-Cu-Cis, which has a cut- off frequency of about 5 kHz. Since many short-wave stations operate at 5 kHz channel separation, the filter provides effective adjacent-channel suppression. The audio signal is then amplified in T< and Ts whose gain is sufficient to enable a pair of high-impedance headphones to be driven from the AF output across Cn-Cn. If the audio output is used to drive an ad- ditional AF amplifier, the value of C19 should be reduced to 1 mF. The signal at the drain of Tz is also fed to buffer Tz, whose output may be used to drive an external fre- quency counter. This is a very useful means of obtaining a read-out of the frequency of the received signal, which makes operation of the re- ceiver immeasurably easier. justing Cs till oscillations just occur: this is indicated by a whistle in the headphones or loudspeaker. The input level is then set with Pc if this is too high, cross modulation occurs, ie. apart from the wanted station, others are also audible. If the aerial signal is too weak, the detector does not operate correctly, and the signal is hardly audible It may be necessary to adjust ?> slightly before optimum perform- ance is achieved: only when this is so, does the frequency counter indi- cate the frequency of the received signal. Construction various short-wave bands are given in Table 1, It is imperative for correct operation of the receiver that the coils are wound in the direction shown and that correct polarity is ob- served (this is facilitated by the large black dots in the circuit and on the coil drawing). The receiver is constructed on the Universal RF Board Type 85000, which is available through our Readers’ Services. As it is an un- pierced copper-clad board with fifty- seven isolated islands and three isolated tracks, it is also available from most electronics retailers. A suggested component layout is shown in Fig. 3. Chokes Li and Li are commercially available components, but inductor Li must be wound as shown in Fig. 2. The number of turns for the Operation For optimum performance, the Gi-D section of T; should just oscillate. This is achieved by setting Pi to roughly its centre of travel and ad- Fig. 2. Circuit diagram of the short-wave re- ceiver. R>;R? = 100 k Ri - 27 k R* = 100 2 Rs;R* - 470 2 R- = 82 9 R. -220 2 R« = 4k7 R.o -220 k R.i =56 k Ru = 560 2 Rn -68 2 Capacitors: C. = 100p C«Cii;Cij=100n Ci = 10 n ceramic C*;C« = 1 n ceramic Cs = 10 p trimmer C* = 1 p Cr = 68p NPO Ce = 40 p trimmer Cs = 82 p NPO Cio = 100 p variable capacitor Ci* = 10 n Cu=22 n C«=330 n Cn = 10 pF;16 V C«=47 n Ci»=47pF;10 V Metal case of about 135' 150 x 75 mm Fig. 3. Suggested component layout of the short-wave re- ceiver. -39 HOW MUCH LONGER WILL SILICON BE USED? 1 II sounds rather strange, against the background of the present development ot microelectronics, to ask how much longer silicon will be used. The first quantities of one-megabit dynamic memories using existing silicon technology have been announced recently while four-mega- bit dynamic memories are expected in 1988. These are the most outstanding current examples of the state of the art of silicon microelectronics. These | developments in large- scale integration (LSI) have been due to process tech- nology or, to put it the other way around, it was mastery of process tech- nology that made this progress in large-scale in- | tegration possible. A reduction in costs per bit on an integrated device went hand in hand with this large-scale inte- gration. This is demonstrated by Fig. 1, which shows the evolution of costs per bit for the various gener- ations of dynamic RAMs as "learning curves". The learning curves for one- megabit and four-megabit dynamic RAMs are esti- mated values. Before turn- ing to the question of the limits of silicon technology and its replacement by gallium arsenide, we shall first briefly outline the development of silicon technology. By the standards of micro- electronics, silicon tech- nology is a "very old" technology. It was 25 years ago, in 1961, that the first 1C was developed by Kilby in germanium and one year later in silicon. This process led in only 25 years from a small number of transistors on a chip to more than one million transistors in regular logic devices on the one hand and to more than a hundred | thousand transistors on a I chip in non-regular logic I devices on the other hand. In other words, the complexity of the circuitry has increased by more than a hundred thousand times in this period of time. After these developments, is a competitor now ap- pearing on the horizon in the form of gallium arsenide? The worldwide market potential of gallium arsenide is estimated at 3.2 billion dollars for 1992, a con- siderable amount when one considers that, eg., the German microelec- tronics market was worth about one billion dollars in 1985. Against this background, one might after all be justified in asking how much longer silicon will be used. In order to answer this question we shall consider the follow- ing points: • the mechanisms of substitution which result in the replacement of a technique or technology by another: • the limits of silicon; • the limits of integration techniques; • the development of the market for silicon and gallium arsenide. Mechanisms of substitution A technique or tech- nology is only replaced by another under the fol- lowing conditions: • Techno-economic limi- tations of a technique become apparent, i.e. substitution results in cost savings. • A faster evolution of an alternative technique is expected and at the same time a tendency towards greater efficiency. In such a case a substi- tution is frequently made as a future investment. • As well as the actual replacement of the existing technique, a new technique promises com- pletely new applications. A substitution is made with a view to innovative po- tential. Limits of silicon I In order to assess the limits of silicon and possibilities I of the alternative material ] gallium arsenide, it is first necessary to consider the physical properties and also the technological status of the two materials. A comparison of the physi- cal properties of the two basic materials reveals three salient factors: • the much greater elec- tron mobility of GaAs, which means that con- siderably faster circuits can be realized with GaAs; • the much greater ther- mal stability of GaAs and greater resistance to radiation, which would be of particular advantage with very fast and highly integrated memories; • a worse ratio of elec- tron mobility to defec- tive electron mobility in the case of GaAs, which also means that com- plementary electronics can be less easily used in GaAs than with silicon. The physical properties Fig. /. The evolution of relative costs per bit for dynamic MOS-RAMs. Table 1 Technologici surface smoothness Chip surfaces Components / 1C only represent one side, I however. In order to make a final judgement we also | have to take into account the state of the art in the two technologies. This has been done for silicon and GaAs in Table 1. If we look at this table, we see that the fault density for silicon chips is more than a thousand times less than for GaAs. This is due to a considerably greater uniformity, purity, and sur- face smoothness in the J case of silicon chips-, in J other words, as a starting material silicon can be much better controlled than GaAs, which in turn j results in far greater ef- ficiency. We can also see that silicon chip surfaces are now more than | 50 mm 2 in size, compared with -10-15 mm 2 for GaAs, in | other words considerably larger and more complex ICs can at present be fabricated with silicon. | On the basis ot this table, I it can be said that GaAs is | at present technologically about a hundred times behind silicon in com- plexity, or more than two \ generations of compo- nents behind. The same I conclusion is reached if one considers the evol- ution of the complexity of integrated circuits, as : shown in Fig. 2. The thick line represents the evol- j ution of the complexity of silicon circuits and the thin line the evolution of GaAs circuits. We can see how silicon has evolved to the four- and 16-megabit dynamic RAM, while GaAs has developed to the four- kilobit RAM. Fig. 2 does not show the production status of these circuits but the time at which the first design models were pre- sented. If we look at the two curves for silicon and GaAs, we have to con- clude that, even if we as- sume a more rapid devel- opment for GaAs than for silicon, it will not attain the degree of complexity of silicon until 1995. Such a rapid development of GaAs is not to be ex- pected and we should as- sume that the broken line with shorter strokes is more probable, so that even in the year 1995 we can ex- pect a difference in com- plexity of more than ten between silicon and GaAs. I If GaAs is not going to catch up with silicon in the next ten years as regards complexity, what about the advantage of greater speed which com- ponents constructed on GaAs have? An indication is provided by the evolution of the gate delays of integrated circuits based on sili- con technology. As an example, Table 2 shows how gate delays in MOS processes in the Volvo plant (part of Philips GmbH in W-Germany) have developed from 1979/80 to 1986. together with the expectations for 1988. Along with the reduction in the smallest geometries and the associated re- duction in gate delays we can also observe a simul- taneous increase in the size of the chip surface | and in the number of components per chip and per mm 2 . This means, therefore, that not only the individual components on the chip have become faster, but that the total chip sizes and number of components have grown very rapidly. At present chips are produced which are 40-50 mm 2 in size, while chips up to 100 mm 2 are being developed and will be produced in 1987. This implies that from 1988 chips between 50 and 100 mm 2 will represent the state of the art. At the same time, the length of the circuit on such chips will also increase, so that a length of 10 mm on a chip of approximately 80 mm 2 will not be excep- tional. If, however, we wish to determine the propa- gation delay on a circuit which is 10 mm in length and assume a value of 10 10 cm/s for the signal propagation, we obtain propagation delays of 0.1 ns. This means, there- fore, that with chips whose geometry is smaller than 1 / = I p.MKT Cl2:C 13 = 470 n Resistors: fffoos: smoothing capacitors supply board preamp board 1 W resistors, before proceeding d con- with the connection of the power-on 1 for the delay and protective circuitry. Note if it is the ground connection on the for power-on circuit; it should be run lo :r- direct to the centre tap of Trz to pre- iph- vent the 10 ms charge pulse for C7 \g. from causing hum on the supply •eration lines to the preamplifier. W into The power-on and protective circuits may now be tested; switch on the mains and verify the delayed action of Re i and Re2 in that order. Apply- ing a direct voltage, e.g. the + or -12 V supply rail, to either one of the protection DC sense inputs L or R should immediately deactivate loud- speaker relay Re2; the ground ter- minals for delay and DC sense cii cuits should be temporarily connec- ted for this test. When wiring the L and R inputs to the loudspeaker lines, remember to make the con- nections direct to the amplifier out- puts, that is, not behind the Re2 contacts! The construction is next proceeded with the wiring around the toroidal power transformers Trt and Trs, taking due care not to confuse the X, Y and Z points. Brake resistor R59 should be mounted on a set of soldering tags. Also remember to fit all mains wiring in an absolutely safe I 11-52 the point from which the earth return (o) wire to the amplifier boards is run. Since this wire does not carry high currents, it need not be as thick as those for the ±75 V rails. The 14 Fig. 14. Connec- tion diagrams and bridge con- figurations at the amplifier outputs. Note that the minimum loud- speaker im- pedance in the bridge set-up is 8 ohms, and refer to the text for details on the loudspeaker polarities. ground terminals on the power amplifier boards, marked @, are next wired to the corresponding ter- minal on the driver supply board. Since this point is also the ground terminal for the preamplifier board, the signal wires between drivers and preamplifier should have their screens connected at the preampli- fier end only. The preamplifier ground input con- nections should be isolated with respect to the amplifier enclosure, and it is best to purchase two Type XLR connectors for this purpose (see parts list). The amplifier's metal enclosure is connected direct to the mains earth line, as well as to the central ground terminal on the + 75 V supply, using a 100 Q resistor. Finally, the construction of the high- power AF amplifier is illustrated with a number of photographs in this article, offering suggestions regard- ing possible enclosure construction and wiring methods (note the pur- pose-welded framework to hold the PCBs and heavy parts). Keep in mind that a sound mechanical construc- tion is paramount to reliability and the ability to resist the kind of rough treatment an amplifier of this type is likely to be forced to endure. Testing After the amplifier has been com- pleted, it is time to check its correct operation. In case you have been patient enough not to test the power output boards as yet, start off with re- placing the 6.3 A fuses with 22 Q 1 W resistors, and turn the quiescent cur- rent presets (Pi) fully anticlockwise. After switching on the amplifier, no voltage should be measured across these fuse substitutes. Should the tion-free amplification within the fre- quency bands and signal level range given in the feature list of article (See Elektor India June 86) There is one final point to make con- cerning the loudspeaker polarity in the stereo set-up (Fig. 14); note the reversed polarity of the loudspeaker at the R output; this is the result of the 180° phase tum occurring in the in- verting opamp in the preamplifier. However, if the wiring to the loud- speaker output sockets is made as shown in Fig. 14, this oddity need not concern the user once the amplifier is fully operational. Finally, the bridge configuration re- quires the amplifier to be driven monaurally at the left-hand channel TS;TW loudspeaker relay remain off after the power-on delay, there is bound to be something amiss in the MOSFET output stage. Now check all supply voltages in the amplifier before pro- ceeding with setting the quiescent current to 400 mA per 75 V supply rail (ie. 0,4 V across each 'fuse'; 100 mA per transistor). The voltage levels given in circuit diagram Fig. 3 may now be checked, at the same time pay due attention to equal cur- rent distribution among the power MOSFETs, ie. each group of parallel- connected source resistors should drop about 25 mV. Large differences in this respect may cause some of the transistors to provide all the power to the load, while others are idle. Leave the amplifier switched on for some time to verify its thermal stab- ility under quiescent current con- ditions. The remainder of the test procedure includes checking the output power capability and distor- selex-i7 When a multimeter is used for measurement, there can be two types of errors: genuine measuring errors, and errors which are not really measuring errors! Even the specified technical data for electronic J components allows for deviations as high as 10% The carbon film resistors show tolerance values of +5% or t10%. Capacitors with ± 1 0% tolerance are considered to be very good. Transistors are tested after manufacture and classified according to their current amplification factor. This classification is designated by a letter or a number appearing after the type number of the transistor, i e. BC147B). Inspite of values of the current amplification factor within a group deviate from each other by more than +30%. In case of components like electrolytic capacitors, the specified values may also Nevertheless, most of the circuits function correctly in spite of considerable component tolerances. Where accuracy is required, suitable compensations Whenever we find that a measured value deviates from a specified value, we must first see if this is due Measuring Techniques Chapter 3 to component tolerance. We must also consider whether the deviation has an effect on the functioning of the particular circuit. It is not possible to make any generalised statement about the effect of such deviations on the circuit performance, because the deviations vary from component to component and the effect is different for different Let us take an example to see how a genuine irrespective of the actual measuring accuracy of the measuring instrument. Figure 1 . shows a voltage divider made of two 100KU resistors and a 4.5V battery connected across the selex combination. Theoratically. I these two resistors must divide the battery voltage of 4.5V into 2.25 + 2.25. Now let us connect a multimeter across R2 and measure the voltage across R2. Surprisingly it is only 1 ,8V The cause of this measuring error is the current drawn by the multimeter itself. This current is the result of I the internal resistance of j the multimeter. This value | can be calculated from the j Ohms per Volt specification | of the multimeter. The internal resistance is obtained by multiplying the [ ohms per Volt value by the j measuring range in volts, j Thus a multimeter with 20KU per Volt being used on 10 V range will give the I internal resistance Ri as follows : 3 iff Ob ■ 4,5 V 1 11 'Ll D : ’[ i | j- ;• . t 83717X-3 Ri = 10V « 20Kfl/v = 200 K!1 As this is effectively connected in parallel with the 100KJ! resistance in our above example, the equivalent resistance becomes 67KH. The potential divider thus becomes a combination of j 100K!! + 67KI1. The voltage across R2 thus becomes 1 -8 instead of 2.25. The voltage being measured is really 1 .8V as shown by the multimeter. The voltage across R2 changes due to the presence of multimeter ) and the measured value is falsified. To get over this difficulty, the meter can be connected as shown in figure 3, The voltage across R2 is not measured directly, but compared with another voltage across the potentiometer PI. The difference in voltages will be shown by the multimeter, and will become zero when the two voltages are equal. The meter does not draw any current in this condition as voltages on both the The potentiometer can have a directly calibrated dial to read the voltage, or we can now measure the voltage across the sliding contact of PI independantly II >he total value of PI is k r> low enough, the internal resistance of the multimeter will not affect the reading. Another way to get rid of this problem is to use a high impedance input circuit with the multimeter. The schematic diagram of such a circuit is shown in figure 4 The impedance converter contains an amplifier which requires a very low input current and gives a high output current which is proportional to the input current. An emitter follower of ordinary transistors, and a source follower circuit can be used in case of FETs. The input voltage is not amplified by the amplifier and thus the measured voltage is indicated accurately by the multimeter without drawing input current from the voltage under test. Effectively, the Ri of the multimeter can be said to have become very high. In case of an emitter follower, the theoretical value can be The high impedance atiachmem lor estimated as follows. The effective Ri is the product of the current amplification factor of the transistor and | the parallel combination of | Re and Ri of the multimeter j As RE is much smaller than | Ri, we can have Ri (effective) = RE x Current Gain. Assuming that RE = | 4 7 Klland current gain = | j 250. the effective input j impedance Ri = 1.18 Mil. Thus the multimeter can I now be said to have an j input resistance of about 1 Mli| which is sufficiently high for I j most measuring applications. | 11-56 elslaor in Measuring Power With A Multimeter selex The ability to convert a specific quantity of energy in a specific period into another form of energy is called power. Speaking in electrical terms we can say p (t) = u (t). i (t) where p(t) is electrical power, u(t) is voltage and i(t) is current. In case of DC currents and voltages the relation becomes P = U.l Capital letters are used for DC quantities which are not a function of time, that is, they do not change with time. Lower case letters are used for Alternating quantities, and to show their dependance on time they are written as p(t). u(t), i(t) etc. Let us first look at the DC quantities. Figure 1 shows | U. I and P as steady levels ] (DC quantities). The current I flows through a resistance R and the voltage across that resistance is U. All I these values do not change I with time and hence at any j given time the following relation holds good; P = U.l I Now for example let U = 24V, I =2 A then we have the P = 24V x 2A = 48W Here the W stands for Watts, which is the unit of the so called DC power. You must have noticed by now that measuring DC power with a multimeter is very simple! Just measure the voltage, then measure the current and then multiply them to get the DC power. ill -57 11-58 eleklor i selex 5 Ohmic resistance. The same quantity of heat could also be produced by a direct current. This particular value of direct current is called the effective current. The effective current is greater than the average value by 1 1% For example, the mains supply voltage is 230V (effective value), where as the average value is only about 207V. If we connect the multimeter across the mains outlet, it reads 230V, because it is designed to read the effective value in the AC ranges. The scale of the multimeter is calibrated in such a manner that it directly reads the effective alternating input. This is well suited for our requirement of power measurement. The effective values of current and voltages are also called RMS values. Without going into the details, we can just note that RMS stands for Root- Mean-Square. This notation comes from the fact that for a sinusoidal alternating waveform the effective value is the square root of the mean of the squares. Using the effective (or RMS) values of voltages and currents, the same formula that is used for DC quantities becomes valid P = U.l This can be further simplified by using the 1 = U/R Thus the power equation becomes P = U’/R From this relation, the power measurement becomes still more easier, because we need only one measurement - that of the voltage across the loudspeaker, Resistance (impedance) of the loudspeaker is specified on the loudspeaker as either 8.0, 40 or 20. measure the voltage, square nd divide it by the loudspeaker impedance. For (ample, if we read 4.5V across the loudspeaker, and if the loudspeaker has 80 impedance then the effective power is 2.53W These measurements are -ied out at a standard ut frequency of IKHz as be seen from figure 4. The measurement however II depend on the amplifier What is of real interest is the non-distorted power output. To decide this, it is better to believe in one's own ears. A headphone can be connected as shown in figure 4. to check for exact setting of the amplifier volume control where distortion just sets in. The voltage can be measured at this setting and then from the loudspeaker impedance, the non-distorted power output can be calculated. The 1 KHz sinewave generator can be constructed as shown in figure 5 and 6. Component list is also provided for the circuit. For the same output voltage the effective power output depends on the loudspeaker impedance. This can be confirmed by setting the sinewave generator and the amplifier for an output voltage of 4.5V and then changing the loudspeakers from 811 to 4(1 and then to 211. The 8(1 loudspeaker has about 2.5W, the 411 loudspeaker has about 5W and 2 1! loudspeaker has about 10W. If the amplifier is not rated for 10W output, distortion will set in with a 211 loudspeaker, -59 selex Power Calculations The most important formula used in power calculations P = U.l which means that electrical power is the product of current and voltage. Another thing that becomes clear from this relation is that voltage or current deliver any power output. A very common example of this is the crackling noise we sometimes hear while taking off a synthetic pullover. This noise is sparks generated by the static electricity. The voltages involved can be as high as 10KV. However these sparks do not harm us as the currents produced are negligible. The power is measured in Watts, and a Watt is defined as follows: 1W = IV . 1 A If any two of the three quantities in the power equation are known, the third can be calculated bicycle dynamo produces upto 3W at 6V. So the current produced by the dynamo is I - P/U = 3/6 = 0.5A Half an Ampere is not a very high current but it serves the purpose of lighting 3W bulbs at 6VI Here the voltage and current are both small and produce a small power | output. However if we take the same current (0.5A) from out mains supply of 230V, the power output produced will be (230V) . (0.5A) = 1 1 5W which is a substantial value. The difference is due i to the higher voltage. From j this we can clearly see that voltage and current both play an equally important role in producing power Let us consider a practical situation. A 100W bulb connected to mains suply of 230V Its current can be I calculated as : I = P/U = 100/230 = 0.43A And using the Ohm's law for calculating the resistance, we have 230V R = 0.45 A This must be the resistance of the bulb. Surprisingly, a measurement of the bulb resistance with a multimeter gives a very low reading: about 30 to 40!!. What went wrong? our calculations, or the multimeter? Both of them are correct, and the 3 multimeter was the resistance of the cold element and what we calculated was the resistance of the hot element when bulb is glowing. When the bulb glows, there is a strong movement of electrons inside the glowing wire and the effective resistance increases. Unfortunately the mains voltage remains same even when the cold bulb is switched on across the mains supply. This gives rise to a very high initial current given by 230V I - U/R - = 7.6A 30!1 This initial current flowing into the bulb lights the bulb and the element is instantly heated up. The resistance then increases to about 535!! as seen before. The initial power drawn by the bulb is enormous : P = (230V) . (7.6A) = 1 748 W = 1 .75 KW 1 -60 MUO. India selex The Digilex-PCB is now available! Price: Rs. 85.00 + Maharashtra Sales Tax. Delivery charges extra: Rs. 6.00 Send full amount by DD/MO/PO. Available from: precious ,0 ELECTRONICS CORPORATION Journal Division 1 1 . Shomroo Vrttial Marg (Kiln Lane) Off Lomington Rood. 8ombay-400 007. ill-61 MICROCOMPUTER DEVELOPMENT SYSTEM PROFESSIONAL-1 Isa Microcomputer Development System, useful for developing completely the hardware and M/S PROFESSIONAL ELECTRONIC PRODUCTS Opp: Old Octroi Post Delhi Road PB. No. 316 Meerut-260 002 GAS/SMOKE DETECTOR Abhitron have developed a gas/smoke detector for protection against accumulat of gases like LPG. ethane, propane, carbon monoxide el detector ii M/S ABHITRON INDIA 386 F/39 Mandodan B. Near Badam Wadi Li Road Girgaum. Bombay-400 =P BASED DATA LOGGER ADVANI OERLIKON have developed a microprocessor based Data Logger for | 230V AC a 1 1 -62 .<* oting ref. No. PI 3/7/86 to M/S. ADVANI OERLIKON L TD. Post Bos No 1546 METAL OXIDE VARISTORS (MOVs) transient voltage suppressors suppressing high voltage spikes' and surges appearing on AC/DC lines, 'o acceptable systems from failures. MOVs are recommended for use in Thyristor Control Systems. SMPS. Voltage Stabilisers. PLCs. Electronic Timers. Computer Systems, Television and VCRs. HiFi Systems. Relay protection and a wide range of other equipments. MOVs of internationally acceptable quality have been developed by Elpro International Ltd— an affiliate company of General Electric Co USA. Devices are now available locally in a wide range of operating voltages For detailed information, write MECO INSTRUMENTS PRIVATE LTD. Bharat Industrial Estate T.J. Road. Sweree Bombay - 400016 M/s. Component Technique represent American Electrical Heater Co. for their range of Heavy duty soldering irons marketing under the name AMERICAN BEAUTY- FEATURES Seamless Steel Casing. One piece. Round. Lighweight Rugged. Long-Life Element. Nickel- I Bombay 400 021 AUTO RANGING DMM MECO have introduced theii Auto-ranging Digital Multim designated as MECO 1210. The | high 3'? digit LCD single range Safety cc pull out ( safety foi tick heat. Easily ar replaced, wattages and tip andle. Selected Modular construction. 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Industrial Development Area, Patancheru 502 319, Medak Dist, Andhra Pradesh Tel.: 208, 209 & 381 (STD Code 08453) • Telex: 0152-222 GRSC LCD Thermometer Issue No. 26 EPS No. 82 156 Simple! Easy to assemble. Based on 1C 71 06 This thermometer is very accurate with a temperature range — 50°C to + 1 50°C. Ideal for house or laboratory. Complete kit (with cabinet) Rs. 575.00 Capacitance Meter issue No. 11 EPS No. 811012-1/2 To measure those elusive farads, this project features — Read out on a 3 1 /2 digit LCD — A measuring range from 0. 1 pf to 20 mfd. — high accuracy. It is a complete instrument at a hobbyists price Complete kit (without cabinet) Rs. 750.00 Digilex Digital Trainer Teach yourself digital electronics in a simple, unique manner. Broaden your horizons and improve your fundamental understanding of the changing world of electronics around you. This trainer gives you an opportunity to learn electronics at a very reasonable cost. Complete trainer at Rs. 325.00 Junior Computer Kit This kit enables you to have a practical orientation of the concepts explained In the Junior Computer Book I. Get actual ‘hands — on’ experience. Learn the basics of hardware and software in an innovative step - by - step manner. And that too at an incredibly low simple system enables you to add price-! each copy as it arrives and to Complete kit (without cabinet) remove a single copy without Rs. 1 500.00 disturbing the others. Elektor Binder - This reddish 25 00 p |us «*• 5 for Packin 0 binder collects your loose copies of « Postage. Elektor into one handy volume. A Kits currently available Issue No. EPS No. Title Price. 33 85110 Telephone Exchange Rs. 1200.00 36 9827 Magnetiser Rs. 65.00 37 80054 Talk Funny Rs. 210.00 39 86013 Single Trace CRT Convertor Rs. 190.00 39 9967 VHF/VHF Modulator Rs. 105.00 28/29 85447 Fault finding probe for Ups. Rs. 60.00 28/29 85431 Hi-fi headphone amplifier Rs. 75.00 Buying one of our Idts will save you the frustration of tracking down those elusive components that hold up your projects. General information. Ordering Information 1. All payments in Advance by M.O.RO or D.D. only. 2. Items will be send by R.P.P only 3. Price includes Packing & Postage. 4 For orders out of Maharashtra state. Please add 10% as a 'Incidental Charges' Send payment to # previous -*■ ELECTRONICS CORPORATION Journal Division 1 1 , Kiln Lane, Off, Lamington Road, Bombay - 400 007. • I DC Card Edge Connectors (20. 26. 34. ,) • 57 Microribbon IDC Connectors (M & F) id Hoods (9. 1 5. 25. • 25 PinMicroribbon IDC Connectors For fully detailed information send your inquiry today! £#*****■&* € V* ’ tJausa Elaslfcifcs Pla. Hi -67 classified ads. ,»r:: IC's — All type Capacitors’ Rubycon. Radial 2200 uF 50V Rs 25 - 3300 Hurry Wonder Musical Bell. (UM 3481/82/83/84) Twelve Melodious uF 50V - Rs 30 . Diodes in 5408 Rs 3 50 IN 4003 etc. and many other time^ Complete kit your s for lust Rs ware, many more Send inquiry with To INTELLIGENT ELECTRONICS. 65 51. Vishwak Artek Apis, Bandra (East) 440022 6407901 CORRECTIONS lished in Elektor Electronics over the past year, the alarm had the fa- cility of incapacitating the ignition system when the alarm is set. It has therefore, better to connect the an 18k resistor instead of to the col- lector of Ti. Indoor unit tor satellite TV reception - 1 the relay that incapacitates the ig- nition system to break the supply to 1. Owing to a processing error at the printer's, the lines between VHF Preamplifier (May 1986 p-32) The value of capacitor Cs should Cs and MX. pin 1, and that be- tween Rs and the collector of T*. have short, yet incorrect gaps. Als the T. base resistor is badly blurred; this is Rs. 10 k. Car burglar alarm Fig. 6. the resistor identified R2 in the LOi section should be Rrc. As drawn, the voltage across relay 3. Please add to Fig 5d: C iso lating bush. ad/ertisers index ADVANI OERLIKON APEX ELECTRONICS ATRON CREATIVE DATA SYSTEMS CTR CYCLO COMPUTERS' COMTECH COSMIC DEVICE ELECTRONICS DISCO WINDING WORKS ECONOMY ENGINEERING ELECTRONICA ELTEK BOOKS ENGINEERING SYSTEMS GREAVES SEMICONDUCTORS IEAP J M ENTERPRISES KLAS ENGINEERING KUSUM SALES LEADER ELECTRONICS LEONICS MECO INSTRUMENTS MELTRON NCS ELECTRONICS PECTRON PIONEER ELECTRONICS PRECIOUS PHILIPS SAINI ELECTRONICS SCIENTIFIC SONODYNE S M J ELECTRONICS S.S. INDUSTRIES SUPERB 11.14 SWASTIK THERMAX TRIMURTI TESTICA TEXONIC VALIANT VASAVI VISHA 11.04 11.70 11.64 11.09 1 1.69 1 1.66 1 1.14 11.76 1 1.67 11.10 11.70 1115 11.63 1 1.08 1 1.71 11.74 1 1.72 1112 .1.10 I 1.73 11.13 11.70 11.70 1 1.64 11.65 11.07 11.68 11.64 11.02 11.11 11.12 11.68 11.05 11.66 II 08 1 1 ' 1 4 11.75 11-74 •lekto Nakamichi AX-1000 Featuring SMPS, a unique advance in audio technology, coming to India for the first time. Vibrating with 250 watts of peak energy, breaking all sound barriers, touching rare heights, -here comes, at last, an Ampli Deck marvel which will fill your senses as never This classic black model — nakamichi AX- 1 000 with its unique Switch Mode Power Supply IS.M.P.S.) has music surging through its sophisticated circuitry, with such sonic purity and clarity, that one hears not the reproduction of musk, but the actual recreation of it. Backed by the audio expertise of Cosmic this latest generation model, lias a dynamic one touch recording system, a super hard perm alloy head, soft touch controls. L.E.D. peak level indicators, double gap erase head plus much much more for over all excellent performance. This powerful Ampli-Cassette Deck has arrived, to cast a spell even on the perfectionist. So get ready for some hypnotism. Cosmic Nakamichi AX-1000 It's pure black magic cosmic We are sound Primer &• Publisher - C.R. Chandarana. 2, Koumari, I4lh A Road. KJiar. Bombay 400 P unt ed , at I rupli Offset. 103 Vasan Udyog Bhavan. Tutsi Pipe Road. Lower Patel. Bombay I 052. 400 013.