SYSTEM SENSITIVITY ADJUSTMENT

TM 11-5820-917-13

Increase the input signal 55 dB and adjust gain control R 168 until the bar-

graph reaches the top of the display. Decrease the gain by one cell.

Repeat steps a through c until no further adjustment is needed.

e. Allow the RCS- 4B to run one full sweep with -120 dBm input. The AGC bar-

graph

5-19. SYSTEM SENSITIVITY ADJUSTMENT. The Chirpsounder record display

should be present on the CRT with signal levels as low as -137 dBm into the 4028

receiver or -130 dBm into the 6043 power divider. The display should not be

present for signals weaker than -147 dBm into the 4028 or -140 dBm into the 6043.

This can be adjusted with the slicing level adjustment, accessible through the top

of the display logic (1A2) module. Use the test setup as shown in figure 5-1

(signal into the 4028). Decrease the signal level to -137 dBm. A solid line should

be present for a minimum of 80% of the full sweep (2-30 MHz). To increase sensi-

tivity, adjust the slicing level control counterclockwise and, conversely, to de-

crease sensitivity and reduce background noise, adjust the slicing level clockwise.

5-20. SPECTRUM ANALYZER BANDWIDTH ADJUSTMENTS. The 500 Hz band-

width is controlled by ramp length R56, gain R37, and DC R49 adjustments on the

1A1A2 assembly (figure FO-10/5). The bandwidth adjustments are made as

follows :

a. Assemble equipment as shown in figure 5-1. Synchronize RCS- 4B with

TCS-4B using the 2-30 MHz sweep with a -80 dBm sweep input to the receiver

(connect to J1 on 4028).

b. Connect a frequency counter to 4028 rear panel BNC connector J9 Base-

band Out. Fine adjust RCS- 4B synchronization using Manual Sync (at 1

Make no further sync adjustments for

the remainder of this test.

Then connect equipment as shown in figure 5-2.

d. Set the audio oscillator for approximately 0 dBm (50 Q) , and 200 Hz. Ob-

serve two horizontal traces on CRT near top and bottom of Chirp sounder record

display area.

e. Slowly increase audio frequency until one trace disappears and note the

audio frequency as measured on the counter. Continue to increase audio frequency

until the remaining trace disappears and note audio frequency. Both frequency

f. If adjustments are necessary, remove the module 1A1 cover to access the

spectrum analyzer output board 1A1A2 (2006-2002).

Connect an oscilloscope to E35 (SYNC A). Adjust R56 until the positive

This pulse goes high for 59 msec

going (+4V) pulse

once every second while the sounder is sweeping.

5-9