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AUDIO CIRCUIT BOARD 800–194 ADJUSTMENTS.
1. Connect an audio voltmeter to Pin 1 (modulator audio) of audio circuit board 800–194. Connect a jumper
between terminal 1 and 2 (the outer terminals) of TB–1 (the 600 ohm balanced input). Connect an audio
signal generator between chassis and either Terminal 1 or 2. Operate the generator for a 100 Hz output at
1 volt. Increase sensitivity of the audio voltmeter until the 100 Hz output component is indicated. Adjust R9
(CMR, Common Mode Rejection) for a minimum common mode output.
2. Set S1 and S2 on audio circuit board 800–194 for 75 micro–second pre–emphasis with S1 and S2 positioned
toward R15. Remove the jumper and feed the audio signal generator into terminals 1 and 2 of TB–1.
Operate the generator to 15 KHz and adjust the level for 0.78 volts (0 dBm) output on the audio voltmeter.
Operate the generator to 400 Hz and observe audio voltmeter. The level at 400 Hz should be exactly 17 dB
below the level at 15 KHz. If not, return to 15 KHz and adjust R15 by the amount in error at 400 Hz. Repeat
process until the exact pre–emphasis is obtained.
3. Modulation meter calibration is covered in the modulator circuit board 800–195 adjustments.
MULTIPLIER CIRCUIT BOARD 800–163 ADJUSTMENTS.
Remove the top cover of the unit. Remove the coaxial cable plug at RF Output jack J2 of on multiplier circuit board
800–163. Refer to the STL–10A ADJUSTMENT LOCATIONS diagram for the location of connectors, test points
and adjustments.
1. Connect a Bird Model #43 Wattmeter with a 5–watt element and a 50 ohm load to J2 of multiplier circuit
board 800–163. Connect sensitive multimeter (0–3 volt DC range) negative probe to TP–1 of multiplier
board and the positive probe to chassis ground. Operate the CONTROL switch to TRANSMIT. A minimum
of 0.25 volts should be indicated. If not, refer to MODULATOR CIRCUIT BOARD ADJUSTMENTS in
the preceding text.
2. Move the meter negative probe to TP–2. Adjust L1 and L2 for a maximum indication.
3. Move the meter negative probe to TP–3. Adjust L3 and L4 for a maximum indication.
4. Move the meter negative probe to TP–4. Adjust L5 and L6 for a maximum indication.
NOTE: Omit this step on the 140–180 MHz units.
5. Move the meter negative probe to TP–5. Adjust C27 and C28 for a maximum indication. Turn "POWER
ADJUST" pot, R14 for maximum power.
6. Adjust C36 and C37 for a maximum indication on the wattmeter connected to J2 with the R14 power pot
operated to maximum. Adjust power level to .75 to 2 watts output.
7. Operate the CONTROL switch to OFF. Remove the wattmeter from J2 and re–install coaxial cable plug at
J2. Adjust R14, "POWER ADJUST", for correct transmitter output power.
RF POWER AMPLIFIER BOARD 800–374B AND 800–373B ADJUSTMENTS.
The RF Power Amplifier is very broad–band and has been fully calibrated and adjusted at the factory. The only
adjustments available are POWER CONTROL POT calibration, B+ adjust, FORWARD POWER METER adjust,
REFLECTED POWER METER adjust, and PA CURRENT adjust. These adjustments should only be made as
necessary and with extreme care by following the procedures below:
For the following adjustments, switch "TRANSMIT" off and connect an accurate RF wattmeter and dummy load
rated for at least 25 watts at 800 to 1000 MHz to the RF output "N" connector. Remove top cover of unit. Please
carefully read procedures before doing them.
POWER CONTROL POT CALIBRATION.
1. On the Interface board, rotate the POWER CALIBRATION POT (R4) fully counter–clockwise.
2. On the front panel of unit, rotate the POWER CONTROL POT fully counter–clockwise.
3. Rotate R20 on the two–stage RF power amplifier board fully counter–clockwise.
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