RECEIVER BASEBAND GAIN ADJUSTMENT

TM 11-5820-917-13

5-17. RECEIVER BASEBAND GAIN ADJUSTMENT. To measure the receiver base-

band gain the 4028 cover must be removed. Then the four screws which secure

the 2A1 and 2A2 assemblies to the chassis plate must be removed. Using the setup

shown in figure 5-1 with the TCS-4B and RCS- 4B synchronized, apply a -70 dBm

signal into the 6043 from the 1024. To determine the baseband gain, attach an

oscilloscope to TP2 on the 2A2A2 assembly (refer to figure 5-6), and check for a

nominal output is outside this range, remove the cover for the 2A2A 2 assembly, and

adjust R110 clockwise to increase gain or counter-clockwise to decrease gain.

5-18. AGC DISPLAY ADJUSTMENT . The offset adjustment (R161) and the gain

adjustment (R168) are located in the AGC output amplifier of the receiver output

section (2A2A2) (figure FO-33/4). They provide position and gain control, respec-

tively, over the AGC analog output before being converted to a digitized bargraph

by the timing and control circuit ( 1A2A2) for display by the CRT. Adjustment must

be performed while the RCS-4B is synchronized (using the 1024 Unit of TCS - 4B

as test equipment). Assemble the test setup per figure 5-1. Synchronize the 1024

and 6025 and proceed with the test.

a. Set the input signal to -120dBm into ANT 1 of the 4028 (bypass the 6043

power divider). Measure signal out of Variable Attenuator' with Spectrum Analyzer.

Adjust attenuator as required.

b. Adjust offset control R161 on 2A2A2 (4028-2002) circuit card to display a

continuous line at the bottom cell of CRT AGC bargraph.

FIGURE 5-1. AGC Display Gain Adjustment Setup.

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