
Model 8640B
TM 9-4935-601-14-7&P
ADJUSTMENTS
5-38. PRELIMINARY FM ADJUSTMENTS (Cont'd)
PEAK DEVIATION Vernier .................................................. Full cw
RANGE ................................................................... 256 - 512 MHz
FREQUENCY TUNE .......................................................... Full ccw
RF ON/OFF ................................................................................ON
2 To set the compensation pot, A3R2, turn generator's LINE switch to OFF. Loosen setscrews in the gear on pot's
shaft. Set DVM to measure ohms and connect it between 936 and 938 wires on the pot.
3. Without changing position of FREQUENCY TUNE knob, rotate compensation pot's shaft until DVM indicates
between 0 and 9 ohms across the two wires.
4. Remove DVM, tighten setscrews, and set LINE to ON.
5. To adjust amplifier offset voltages, set FM switch to DC, and set FREQUENCY TUNE to 300 MHz.
Connect DVM to BUFFER OUT test point, A5TP6, and adjust BUFFER OFFSET adjustment, A5R23, for 0 ± 0.5
mVdc at A5TP6.
6. Connect DVM to A3A4TP2 and adjust OFFSET adjustment, A3A4R5, for 0 ± 0.5 mVdc at A3A4TP2.
7. Connect DVM to OUTPUT test point, A5TP2, and adjust AMPLIFIER OFFSET adjustment, A5R8, for 0 ± 1.0
mVdc at A5TP2.
8. To adjust calibration voltage, set FM switch to CAL, set DVM to measure dc voltage, and connect DVM to FM
BUFFER IN test point, A5TP5. Adjust FM CAL POT, A13R3, for 1.000 ± 0.001 Vdc at A5TP5.
9. Connect DVM to VARACTOR CATHODE test point, A7TP3, and set PEAK DEVIATION switch as shown below.
The DVM should read as specified.
PEAK DEVIATION
DVM Reading at A7TP3
2.56 MHz
<± 5.6 mVdc
1.28 MHz
<± 5.6 mVdc
640 kHz
<± 5.6 mVdc
320 kHz
<± 5.6 mVdc
160 kHz
<± 4.5 mVdc
80 kHz
<± 2.2 mVdc
40 kHz
<± 1.1 mVdc
20 kHz
<+ 0.6 mVdc
10 kHz
<± 0.6 mVdc
5 kHz
<+ 0.6 mVdc
5-28
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