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Dual diversity tuner for FM microphones; Pt.2 Construction & alignment of the Dual Diversity Tuner does not require any special equipment or tools apart from an alignment tool & a tuning wand which can be easily made. There is little wiring involved since most of the parts are assembled onto PC boards. By JOHN CLARKE The prototype for the SILICON CHIP Dual Diversity Tuner was built into a 1-unit high black anodised rack case with screen printed front and rear panels. Two PC boards are used to accom­modate the components: (1) a main board coded 06307941 and meas­ uring 207 x 161mm; and (2) a satellite board coded 06307942 and measuring 28 x 49mm. The latter carries the RF preamplifier components and is shielded by a boxed section made from 15mm-high single-sided PC board. A further strip of single-sided PC board divides this box into two sections, to provide additional shielding for the RF preamplifier components. Following assembly, the shielded RF preamplifier module is mounted 66  Silicon Chip directly on the main PC board. Begin construction by comparing your PC boards against the published patterns to verify that all tracks are intact and that there are no shorts between tracks. Some holes may need to be enlarged to accept the relevant components; eg, the mounting holes for L10, T1, T2, VC2 and for the PC stakes. The hole used to secure the tab of REG1 to the PC board may also need to be enlarged to accept the mounting screw. Note that there are only four holes in the RF preamplifier board. These allow short lengths of tinned copper wire to pass through from the track (top) side of the board and through the main board for both mounting and earthing purposes. Unlike the main PC board, all components in the RF preamplifier are mounted on the track side of the board. Main board assembly Fig.7 shows the overlay diagram for the main PC board. Begin construction by inserting PC stakes at all external wiring points and at test points TP1 & TP GND. This done, install all the low profile components such as the links, resistors and ICs. Table 2 shows the resistor colour code but it’s also a good idea to check them on your multimeter as some of the colours can be difficult to decipher. Take care to ensure that the ICs are all oriented correctly and that each is mounted in the correct location. The 5W resistor is mounted about 1mm proud of the PC board to allow the air to circulate beneath it for cooling. Mount the diodes next but again be sure to use the correct type at each location. Diodes D1-D4 are marked with the BA482 type number and are smaller than the 1N4148 diodes used for D6-D8. D5, the BB119 varicap, looks very similar to a 1N4148, so be sure to check its type number carefully 6 1 5 4 2 BASE DIAGRAM TOP VIEW L1-L4 6T, 0.5mm DIA ENCU WIRE ON PHILIPS 4313 020 40031 BALUN COR 3 5 before installing it on the board. Take care with the orientation of each diode and note particularly that D2 and D3 face in opposite directions. The capacitors can now be installed. There are several different types used on the PC board, so make sure that you always use the correct type at each location. Ceramic capacitors are mostly used in the FM tuner section of the board, while MKT and electrolytic capacitors are used throughout the remainder of the circuit. Table 1 lists the relevant capacitor codes and their corresponding values. Make sure that the electrolytics are cor­rectly oriented. Note particularly that the 10µF electrolytic and 0.1µF MKT capacitors near IC3 are installed with their bodies flat against the PC board. You will need to bend their leads through 90° to do this, however. The capacitors are mounted in this way so that the leads to LEDs 1-3 in the bargraph display can pass over the top of them – see photo. Similarly, the 4700µF capacitor near REG1 is also installed lying down –see Fig.6. Its body should be secured to the PC board using silicone rubber compound to prevent possible lead damage due to vibration. The 3-terminal regulator (REG1) is mounted on a small heat­sink. Smear the mating surfaces with heatsink compound before bolting the assembly to PC board. Coils Fig.6 shows the coil winding details. L1-L4 are wound onto a balun former 4 2 3 6 1 2 3 L10 F1, S1 WINDING: PINS 6 AND 1, S2 10.5T, 0.5mm DIA ENCU WIRE T2 WINDINGS: PINS 1, 2 AND 3, 3T, BIFILAR 0.25mm DIA ENCU WIRE PINS 5 AND 4, 4T, 0.5mm DIA ENCU WIRE COILS T1, T2 AND L10 WOUND ON NEOSID TYPE 'A' COIL ASSEMBLY 99-007-96 (BASE, FORMER, CAN AND F29 SLUG) 4 5 6 T1 WINDINGS: PINS 4 AND 6, 3.5T, 0.5mm DIA ENCU WIRE PINS 3 AND 2, 2T, 0.5mm ENCU WIRE NOTE: WIND COILS IN SAME SENSE AS ABOVE L5 1.5T L6 6.5T 1 F2 L7 8.5T L5-L9 WOUND ON 4mm DIA MANDREL USING 0.6mm DIA ENCU WIRE L8 1.5T L9 6.5T Fig.6: this diagram shows the winding details for all the coils in the Diversity Tuner. Be sure to use the wire diameter specified for each coil & make sure that each winding is wound in the direction shown. A complete description on winding each coil also appears in the text & this should be closely followed. (six turns of 0.5mm-dia. ECW), while L5-L9 are air cored and are made by winding the appropriate number of turns of 0.6mm ECW onto a 4mm (5/32-inch) mandril. You can use a drill bit for this. Note that L5, L6 and L7 are wound in a clockwise direction, while L8 and L9 are wound anticlockwise. Wind each turn close to the previous turn as shown in the diagram. T1, T2 and L10 are wound on the Neosid coil formers. Begin by inserting the coil formers into the bases, then wind T1 using 0.5mm ECW exactly as shown. Note that the two windings are wound in opposite directions and should be immediately adjacent to each other. Make sure that you get the winding phases (directions) correct, otherwise the local oscillator won’t work. Note that the enamelled copper wire is easily terminated on the base pins by August 1994  67 S2 .01 D7 10k .01 1 .01 47  0.1 0.1 0.1 .033 K 1.5k 220k IC3 LM3914 GND 10uF 1 A 10k 10k 220k 10k LED1 LED2 LED3 LED4 LED5 LED6 LED7 LED8 LED9 LED10 0.1 2.7k 1.2M 10k 10k TP GND VR3 1 0.1 3.9K 10uF 2.7k 1 330k IC5 LM393 0.1 VR2 82 5W 10k 2.7k TP1 VR1 1uF IC4 LM358 10  300  4.7k 56k 4.7k 1.5k 0.1 47k 220k .001 0.33 27k 1 1 IC2 TDA1576 750  10k D8 0.1 0.1 0.1 33pF .0068 100k 33k 22k IC6 LF353 100k 560pF 39k IC11 4017 X1 X2 33pF L10 100k SHIELD 47k 10  47uF 1 T2 T1 D5 REG1 7812 0.1 3.3k 33pF 10  0.1 .01 15pF 10  390pF 1 .01 390pF 1.8pF 33pF 6.8pF L9 IC1 TDA1574 220k .01 10 .01 220k VC2 6.8pF L8 47uF IC8 74C14 .001 33pF 10uF .01 10  3.9pF .01 1 .01 .001 SHIELD L6 10  SHIELD VC1 IC12 7555 L5 27pF .001 4700 0.1 Q1 .001 1 .01 220k 390 L7 2.2k 22k .01 IC7 4066 .001 SHIELD D9-D12 .018 IC9 7555 .01 2.2k 12.6VAC 0.1 D4 .01 D6 L4 D1 SHIELD 10k ANT B L3 .01 L1 D3 10k .01 L2 2.2k .01 .01 IC10 4013 D2 .01 2.2k ANT A 10  GND 10  GND O/P 10uF 1 47pF VR4 A K A K LED11 RED LED12 GREEN 1 Fig.7: install the parts on the main PC board as shown in this wiring diagram. The RF preamplifier board (top, left) is also mounted on the main board & is enclosed in a shield made from single-sided blank PCB material (see Fig.9). Note that the parts in the RF preamplifier are installed on the copper side of the board, with connections to the main board made via feedthrough capacitors & wire links. 68  Silicon Chip Keep all component leads as short as possible when assembling the PC board, particularly around the FM tuner stages at the top of the PC board. The 4700µF electrolytic capacitor at bottom right should be secured to the board using silicone rubber compound to prevent its leads from breaking. heating the wire with your soldering iron until the enamel melts and then applying solder. T2 must be wound with extreme care. To wind this coil, first take the 250mm-length of 0.25mm ECW, cut it in half and twist the two wires together using a hand drill and a vyce until there is about one twist per millimetre. This done, solder one wire end (S1) to pin 3 of the base and the adjacent end (S2) to pin 2. Wind on three turns as shown, then use your multimeter to identify the other end of the wire connected to pin 3. Solder this end (F1) to pin 2 and connect the remaining end (F2) to pin 1. The other winding between pins 4 & 5 uses four turns of 0.5mm ECW. It must be wound in the opposite direction to the bifilar winding. Note that Fig.6 shows a gap between each turn for the bi­filar winding but this has only been done for the sake of clari­ty. In practice, the turns should all be close-wound (ie, imme­diately adjacent to each other), while the top winding should be immediately adjacent to the bifilar winding. Coil L10 (the quadrature coil) consists of just a single winding. Wind it in the direction shown and terminate the top and bottom leads to pins 1 & 6 respectively. Once wound, the coils can all be installed on the PC board. Mount L8 & L9 so that they sit about 1mm above the board surface. T1, T2 and L10 can only be installed one way on the PC board since their middle pins are offset, but make sure that you don’t get them mixed up. A metal can is then fitted over each coil and is secured by soldering its lugs to the earth pattern of the board. Finally, the ferrite slugs can be screwed into the formers using a plastic alignment tool (available from TABLE 1: CAPACITOR CODES Value 0.33µF 0.1µF .033µF .018µF .01µF .0068µF .001µF 560pF 390pF 47pF 33pF 27pF 15pF 6.8pF 3.9pF 1.8pF IEC 330n 100n 33n 18n 10n 6n8 1n0 560p (n56) 390p (n39) 47p 33p 27p 15p 6p8 3p9 1p8 EIA 334 104 333 183 103 682 102 561 391 47 33 27 15 6.8 3.9 1.8 your electronic parts retailer). Do not use a screwdriver for this job since this will crack the ferrite. August 1994  69 S1 NEUTRAL (BLUE) CORD GRIP GROMMET FRONT PANEL SECONDARY LED12 K ANTENNA 'A' PAL SOCKET LEDS1-10 50  COAX A ANTENNA 'B' PAL SOCKET LED11 AUDIO OUTPUT RCA SOCKET 12.6VAC C NO S2 NC REAR PANEL VR4 COVER WIRING OF S1 AND F1 WITH INSULATING SLEEVING BROWN BLUE POWER TRANSFORMER EARTH LUG EARTH (GREEN/ YELLOW) ACTIVE (BROWN) ACTIVE (BROWN) 250mA FUSE PRIMARY Fig.8: use 240VAC-rated cable for all mains wiring & insulate all exposed terminals on the fuseholder & switch S1 using heatshrink tubing (see text) to prevent any possibility of accidental shock. The mains cord earth lead (green/yellow) must be soldered to an earth lug which is securely bolted to chassis. 70  Silicon Chip The LED bargraph display and LEDs 11-12 can be installed now. The 3mm LEDs used for LED 11 and LED 12 are installed with their leads untrimmed, so that the LEDs can later be bent over and pushed through matching holes in the front panel. Watch the polarity of the LEDs – the anode lead is the longer of the two. The bargraph (LEDs 1-10) must be mounted so that the front of the display is 14mm from the edge of board. This is done to ensure that it will later sit flush with the front panel – see Fig.8. To achieve this, it will be necessary to extend each lead using a short length (about 25mm) of tinned copper wire. Bend the leads at right angles about 6mm above the board before soldering the bargraph in position. As before, take care with the polarity of this device. As with individual LEDs, the anode lead of each LED in the bargraph is the longer of the two and it is a good idea to mark the anode end of the device before extending the lead lengths. RF preamplifier The RF preamplifier board can be assembled now – see Fig.7. Before This photo shows the method used to mount the bargraph LEDs (LEDs1-10). The lead lengths must all be extended using short lengths of tinned copper wire & the leads must all be bent through 90° after soldering so that the bargraph mates with its front panel cutout. mounting any of the parts, it must be mounted copper side up on the main PC board and secured by passing short wire links through the four mounting points (indicated by solid dots on Fig.6). Solder these links at each end to the surrounding copper pattern to secure the two boards together. This done, the parts can be mounted onto the preamplifier board by soldering their leads directly to the undrilled copper lands (ie, the parts are mounted on the copper side of the board). Keep all leads as short as possible and take TABLE 2: RESISTOR COLOUR CODES ❏ No. ❏   1 ❏   1 ❏   6 ❏   3 ❏   1 ❏   2 ❏   1 ❏   1 ❏   1 ❏   2 ❏ 10 ❏   2 ❏   1 ❏   1 ❏   3 ❏   4 ❏   2 ❏   1 ❏   1 ❏   1 ❏   1 ❏   9 Value 1.2MΩ 330kΩ 220kΩ 100kΩ 56kΩ 47kΩ 39kΩ 33kΩ 27kΩ 22kΩ 10kΩ 4.7kΩ 3.9kΩ 3.3kΩ 2.7kΩ 2.2kΩ 1.5kΩ 750Ω 390Ω 300Ω 47Ω 10Ω 4-Band Code (1%) brown red green brown orange orange yellow brown red red yellow brown brown black yellow brown green blue orange brown yellow violet orange brown orange white orange brown orange orange orange brown red violet orange brown red red orange brown brown black orange brown yellow violet red brown orange white red brown orange orange red brown red violet red brown red red red brown brown green red brown violet green brown brown orange white brown brown orange black brown brown yellow violet black brown brown black black brown 5-Band Code (1%) brown red black yellow brown orange orange black orange brown red red black orange brown brown black black orange brown green blue black red brown yellow violet black red brown orange white black red brown orange orange black red brown red violet black red brown red red black red brown brown black black red brown yellow violet black brown brown orange white black brown brown orange orange black brown brown red violet black brown brown red red black brown brown brown green black brown brown violet green black black brown orange white black black brown orange black black black brown yellow violet black gold brown brown black black gold brown August 1994  71 iron for this job and run generous fillets of solder along the joints to hold the shield pieces in position. It is not necessary to solder along the complete perimeter; just solder the boards together where you can. The internal 38 x 12mm board should be installed with its copper side facing L5 and L6. Note that the bottom edge of this board sits about 2mm above the preamplifier board, to provide clearance for one of the transistor leads. With the shield assembly completed, the leads of the ceram­ ic feedthrough capacitors can be connected to the main board and to the RF preamplifier board using short lengths of tinned copper wire. The exception here is the .001µF feed­ through capacitor that’s connected to Q1’s source; it only has one end connected to the RF preamplifier board. The lead at the end of the capacitor on the outside of the shield is simply snipped off. The two link connections are made using 0.6mm ECW. Solder the shield pieces to the RF preamplifier board as shown in this photo & note that the internal shield piece is installed with its copper side facing L5 & L6 (to the right). The ceramic feedthrough capacitors are connected to the main board & to the RF preamplifier board using short lengths of tinned copper wire. 72  Silicon Chip 8 15 A 12 25 15 A 8 care with the orientation of Q1 – its label should face upwards and the longest lead should be adjacent to L7. Do not install the .001µF ceramic feedthrough capacitors yet, since these mount into the shield pieces. Instead, install vertical tinned copper wire links at each capacitor position so that these can later be soldered to the capacitor leads. The two longest shield pieces can now be drilled to accept the four feedthrough capacitors and the two feedthrough links. Fig.9 shows the drilling details. Clean away the copper from around the two link holes using an oversize drill to prevent any possibility of the links shorting to the copper. The copper surrounding the capacitor feedthrough holes should be left intact and tinned with solder. You are now ready to install the feedthrough capacitors. These should be pushed through so that their flanges are on the copper side of the shield pieces – see photos. This done, the metal bodies of the capacitors should be soldered to the sur­rounding copper. 9 22 27 41 53 COPPER SIDE AT REAR OF PANELS ALL HOLES 3mm DIA. REMOVE COPPER AROUND HOLES 'A' DIMENSIONS IN MILLIMETRES Fig.9: here are the drilling details for the two long shield pieces used in the RF preamplifier. Once all the feedthrough capacitors are in, the shield pieces can be soldered to the perimeter of the preamplifier board to form a complete enclosure. Use a fine-tipped soldering Final assembly The completed board assembly is now ready for installation in the case. To simplify the description, we will assume that you are building the unit from a kit which has pre-punched holes and screen-printed front and rear panels. If you are building the unit from a short-form kit, you will have to drill the holes yourself using the PC board and wiring diagram as a guide. Assuming that the holes have all been drilled, assemble the case and attach the four rubber feet to the base. This done, install the various items of hardware on the front and rear panels, then mount the PC board onto the baseplate using 5mm standoffs and 3mm screws and nuts. Check that the LED bargraph display fits neatly into the slot provided in the front panel and insert the two 3mm LEDs into their respective holes. The transformer can be mounted next; it is secured using 4mm screws and nuts. The earth lug is secured using a 4mm screw, nut and star washer. Tighten this assembly firmly, so that there is no possibility of the earth lug coming adrift. Important: scrape away the paint or anodising from around the earth lug mounting hole before installing the earth lug This view clearly shows the three feedthrough capacitors & the feedthrough link on one side of the shield box. Note that the feedthrough capacitor on the other side of the shield box is not directly connected to the main PC board. assembly to ensure a good earth contact. Fig.8 shows the final wiring details for the tuner. Exer­cise extreme care with the mains wiring. Begin by stripping back the outer mains cord sheath so that the leads are free to reach from the back panel to the mains switch (S1) on the front panel. This done, push the mains cord through the entry hole until about 40mm of the outer sheath is inside the case and clamp it securely using a cordgrip grommet. The Neutral (blue) mains lead goes directly to power switch S1, while the Active (brown) lead goes to S1 via the fuse. The transformer primary connections go to the remaining switch contacts, while the secondary leads are twisted together and connected to the 12.6V AC input on the PC board. Note that the lead from the centre tap of the transformer is not used and can be cut off. Use heatshrink tubing to insulate the bare fuse and switch contacts to prevent accidental shock. This is done by sliding some heatshrink tubing over the leads before soldering them. After the connections have been made, the tubing is pushed over the switch and 74  Silicon Chip fuse bodies and shrunk into place using a hot air gun. The green/yellow lead from the mains cord is soldered di­rectly to the earth lug. Leave a loop in this lead so that it will be the last lead to come adrift if the mains cord is wrenched out of the grommet. Be sure to use shielded audio cable for the wiring to the pot and to the output RCA socket – see Fig.8. This shielded audio cable should be kept well away from the power transformer to prevent hum injection into the audio signal. The antenna test switch (S2) can be wired using 3-way rain­ bow cable. Note that some switches do not have the same Common, Normally Open, Normally Closed (C NO NC) pin arrangement as shown in Fig.8, so check your switch before making the connections. The PAL sockets are wired with 50Ω RF cable. Finally, use cable ties to secure the wiring as shown in the photographs. Note that the mains leads should be laced togeth­er so that if one lead comes adrift, it cannot come into contact with the case. Before applying power, it is a good idea to check your work carefully for wiring and component placement errors. In particu­ lar, check that the mains wiring is correct, that all parts are correctly oriented, and that there are no vacant holes on the PC board. Note that there are two test points on the PC board: TP1 and TP GND. You can connect the negative lead of your multimeter to TP GND for all subsequent measurements. Voltage checks Apply power and check that +12V appears at the output of REG1. If it is below this, switch off immediately and check the regulator circuit and for shorts on the +12V rail. If the voltage is correct, check that +12V is present on the supply pin of each IC (ie, pin 15 of IC1; pin 1 of IC2; pins 3 & 9 of IC3; pin 8 of IC4, IC5, IC6, IC9 & IC12; pin 14 of IC7, IC8 & IC10; and pin 16 of IC11). The source of Q1 should be at about 4V, which sets the quiescent current through the device at about 10mA. You should also be able to measure 4V at G1 of Q1 (and on the other side of the 220kΩ gate resistor). G2 of Q1 should be at about +12V unless the tuner happens to be tuned to a very strong signal. This is very unlikely at this stage since the tuner has not been aligned and no antenna is attached. Fig.10 (above) shows the full-size etching pattern for the main PC board, while Fig.11 at left shows the etching pattern for the RF preamplifier board. Check your boards carefully for etching defects by comparing them with these patterns before mounting any of the parts. August 1994  75 Lace the internal wiring together using cable ties & note that the mains leads should be laced togeth­er so that if one lead comes adrift, it cannot come into contact with the case. The shielded audio cable should be kept well away from the power transformer to prevent hum injection into the audio signal. The drain of Q1 should be close to +12V. At this stage, one of the active antenna LEDs should be lit or they may be alternately flashing at about a 1-second rate. In addition, check that the Neon lamp in the on/off switch is glow­ing but do not expect the signal level LEDs to light at this stage. Assuming that all is well so far, you can now move on to the alignment procedure. Alignment Alignment of the tuner requires only a few simple tools. You will need a screwdriver-type alignment tool, a tuning wand, a multimeter and an FM wireless microphone. An alignment tool has a plastic handle and a small tip made of either brass of tough plastic. It must be used because an ordinary screwdriver would detune the coil being adjusted and, as previously mentioned, could easily crack the ferrite cores. The tuning wand (see photo) is used for aligning the RF preamplifier stage. It consists of a short length of plastic tubing with a ferrite core at one end and a brass screw at the other. This tool can easily be made as shown in the accompanying photograph. It decreases the inductance when the brass end is introduced into an air-cored 76  Silicon Chip coil and increases the inductance when the ferrite core is introduced into the coil. During alignment, the multimeter is used to monitor the signal level at TP1, while the wireless microphone is used as the signal source. The step-by-step alignment procedure is as fol­lows: (1). Connect a simple antenna to the antenna A input. A 300mm length of copper wire plugged into the antenna socket will do the job. (2). Adjust VR1 so that the first LED in the bargraph is just extinguished or is very dim (FM microphone off). This will set the meter signal output range. Adjust VR2 and VR3 so that the wiper of VR2 is at 0.8V and the wiper of VR3 is at 0.3V. (3). Connect the multimeter between TP1 and TP GND and set it so that it will read a 0-3V range. (4). Switch on the FM microphone and place it close to the antenna. Now press and hold the antenna test switch to select antenna A and adjust the slug in T1 using the alignment tool until a voltage appears on the multi­meter. Depending on the initial state of tune, the signal strength meter will either show full scale or only a few LEDs will be lit. Adjust T1 for a maximum voltage reading. Note: this maximum voltage must be less than 2.5V, other­wise the meter circuit may overrange and a false maximum may be obtained. To overcome this problem, simply move the FM microphone further away from the receiving antenna. (5). Adjust T2 for a maximum reading, then adjust L10. This done, adjust T1 again (this is necessary since adjustments to L10 retune the local oscillator due to the AFC). (6). Repeat step 4 to obtain the maximum signal. Note that it is difficult to tune L10 if the slug is adjusted too quickly – tune the slug slowly to avoid missing the signal peak. Note also that all three coils may have a small range over which the signal remains at maximum. In each case, find the centre of this adjust­ment range and set the slug to this position. (7). L6 and L9 can now be adjusted for maximum signal. Begin by spreading L6 and L9 so that there is about 0.5mm between each winding turn and adjust VC1 and VC2 for maximum signal. (8). Insert the brass end of the tuning wand into L6. If the signal level decreases, try the ferrite end of the wand. If the signal decreases again, then the coil is correctly tuned. More than likely, the coil will not be tuned and will need to be stretched or closed slightly so that both ends of the tuning wand produce a drop in signal strength. If the signal goes down with the brass end of the wand and increases with the ferrite end, close the coil slightly by squeezing it gently with your fingers. Repeat the above test to see if the coil is now tuned. Conversely, if the signal goes up with the brass end and down with the ferrite end, then the coil will need to be stretched slightly. Retest the coil with both ends of the wand after each adjustment until the tuning is correct (ie, both ends of the wand cause the signal level to decrease). (9). Repeat step 7 for coil L9, then repeat the entire alignment procedure again to make sure that everything is spot on. (10). Switch off the FM microphone and set VR2 (the mute threshold trimpot) fully clockwise. Now adjust VR2 anticlockwise until pin 7 of IC5a just goes low. Antenna installation The antenna requirements for the SILICON CHIP Dual Diversi­ ty Tuner are not particularly difficult. You can use commercial FM dipole antennas, TV “rabbit ears” or 1/4-wave whip antennas. It is not necessary to use antennas with gain such as multi-element Yagis. Dipole and rabbit ear antennas usually have a characteris­tic impedance of 300Ω, so you will need to use a balun transform­er (for TV sets) to match these antennas to the 75Ω input sockets on the rear panel of the tuner. TV balun transformers are avail­able for a few dollars from your local parts retailer. A 1/4-wave whip is simply a 300400mm length of wire which plugs into the rear of the tuner. You can make one up by connect­ing a suitable length of stout enamelled copper wire to the centre pin of a PAL plug. The second antenna must be separated from the first by at least three metres and this is best done using a PAL plug to PAL socket extension lead. When installing the tuner, the antennas should be mounted above the stage or the audience to minimise signal attenuation due to people and room objects. Adjust the audio level pot so that the signal output level matches the mixer or amplifier requirements. After each setup, always test the unit by having somebody move around with the FM wireless microphone. The signal strength meter on the tuner will give you a good indication of the signal strength from each antenna. Use the test switch to select the second antenna to verify its performance and check that the Diversity Tuner au­tomatically switches between the two antennas as the microphone is moved around. SC This home-made tuning wand is used for aligning the RF preamplifier stage & consists of a short length of plastic tubing with a ferrite core at one end & a brass screw at the other. It decreases the inductance when the brass end is introduced into an air-cored coil & increases the inductance when the ferrite core is introduced into the coil. August 1994  77