Section V Models 78 1 OOA, 78 10 1A
Maintenance
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keep signal out of control of the Automatic Gain Control 5-65. IF Gain and Discriminator Alignment.
loop and to see IF signal changes corresponding with input
level changes during steps j - q. 5-66. The following adjustments tune the IF amplifier for
maximum gain and center the IF signal in the discriminator
j. Adjust Z1C 1 and Z2C 1 for maximum signal. operating frequency range. The IF amplifier has two inte-
@ grated circuit amplifiers that are tuned to maximize the
k. Adjust 8656A to 43.64 MHz below carrier frequency. gain at the intermediate frequency. This is accomplished by
Adjust 8656A output amplitude to 0 dBm, then adjust to tuning C5 1 and C60 so parallel resonance occurs at the in-
see image. termediate frequency. The output amplitude measured at
TP5 is maximized by this procedure. An adjustment with
1. Remove cover and adjust Z1C2 to MINIMIZE ampli- C66 then adjusts the center of the discriminator range to
tude of scope display. coincide with the IF signal frequency.
m. Remove cover and adjust Z2C2 to MINIMIZE ampli- a. Place transmitter in test box 00780-63030 with test
tude of scope display. box attenuator set to 0 dB. Do not put test box top cover
on for this test.
n. Change 8656A frequency to carrier frequency. Change
output amplitude back to 40 dBm. b. Connect test box RF output to receiver rear panel
antenna input, 53.
0. Remove cover and adjust ZlCl for maximum signal.
c. Attach 5O:l scope probe (HP 10002C) to HF board
p. Adjust C8 for maximum signal. TP5, Figure 5-9).
q. If necessary, remove cover and adjust Z2C 1 so that the d. Set scope sensitivity of O.OlV/cm and sweep to 0.5
signal is greater than -32 dBm but less than -26 dBm. ms/cm. Observe the p-p amplitude of the scope waveform,
(Figure 5-1 1, A). (This signal is the saturated output of the
r. Replace cover that were removed from Z1C1, ZlC2, IF amplifier.)
ZlCl-, and Z2C2 in steps 1 and m, then remove all probes
and cables. e. Switch the test box attenuator to a position at which
the p-p amplitude of the scope display drops to less than
half of the saturated amplitude noted in preceding step
(Figure 5-1 1, B).
f. Referring to Figure 5-9, adjust C5 1 and C60 for maxi-
mum amplitude on scope, switching in additional attenua-
tion is necessary to eliminate saturation of the IF amplifier.
g. Remove scope probe from TP5 and attach to subcarrier
output pin SUB.
h. Remove battery from transmitter and adjust C66 so a
symmetrical noise picture is obtained at the subcarrier out-
put. Note the peak-to-peak (pp) noise amplitude.
i. Reinsert battery or power supply energized at 8.4V dc
Figure 5- 18. Peak Intermediate Frequency Display into transmitter and plug transmitter back into test box.
Observe a 1 kHz signal, the pp amplitude of which should
s. Remove HF board P2 from rear panel antenna con- be at least 2V pp less than the pp noise amplitude observed
nector and reconnect it to J2 on inside of chassis cover in the preceding step. The 1 kHz signal should be at least
(7810140254). 2V pp in amplitude. If not, repeat step h.
t. Remove power cord from receiver and reinstall chassis 5-67. IF Alignment and AFC Loop Zero.
cover.
5-68. Adjustments are now made on the AFC loop to
u. Reconnect chassis cover cable P1 to antenna connector establish the AFC zero point, which aligns the transmitter
53 inside rear panel. (carrier) and receiver (local) oscillators. At this point in the
5-26 078 100-2 |
ACEC
