Squelch Test

253) volts ac (AN/TRC-68), or at 22 and

(3) Tune the rt unit to 225.0 mc.

(4) Set the TS-497/URR to a test fre-

30 volts dc (AN/VRC-24). The input signal

required to deactivate the squelch must be

quency of 225.0 mc. Set the METER

between 0.5 and 17 microvolt for maxi-

switch to S-METER and tune the

TS-497/URR for a maximum indi-

mum sensitivity, and between 4.5 and 280

microvolt for minimum sensitivity.

cation on the meter.

h. Tune the rt unit to 399.9 mc. Set the

Modulate the TS-497/URR output

(5)

TS-497/URR at the same frequency. Turn

signal at 30 percent with a 1,000-

the METER switch to S-METER and read-

cycle audiofrequency.

just the TS-497/URR for a maximum S-

Adjust the MICROVOLTS control

(6)

METER indication. Turn the MICROVOLTS

on the TS-497/URR until the ME-

dial to 6. Adjust the SQUELCH control for

30B/U indicates 12.25 volts across

the minimum setting that will deactivate

600-ohm load.

the squelch. Turn the MICROVOLTS dial

Recycle the rt unit to 399.9-mc and

(7)

to the minimum setting that will operate

then back to the test frequency. The

the squelch. The signal input voltage ratio

M E - 3 0 B / U indication should be

between the unsquelched and the squelched

within 10 percent of 12.25 volts.

condition must not exceed 2 to 1.

R e p e a t (7) above for test fre-

(8)

quencies of 300 and 235 mc.

149. Signal Plus Noise-to-Noise Ratio

148. Squelch Test

Connect the AN/VRC-24 or AN/TRC-68

Connect the equipment as shown in figure

to the test equipment as shown in figure

115. Connect the ME-30B/U and variable

115.

autotransformer or the ME-26/U and po-

a. Set the TS-497/URR to the same fre-

tentiometer as shown in figure 114.

quency as the rt unit and tune the TS-497/

a. Tune the rt unit to 399.9 mc.

URR for a maximum indication on the S-

b. Set the SQUELCH control to the maxi-

METER.

mum sensitivity position (fully counter-

b. Adjust the TS-497/URR for a 10,000-

clockwise to the stop but not to OFF).

microvolt output modulated 30 percent with

c. Turn the METER switch to S-METER

a 1,000-cycle audio signal.

and tune the TS-497/URR for a maximum

c. Adjust the rt unit VOLUME control

indication of the S-METER.

f o r a 24.5-volt root-mean-square (rms)

d. Adjust the TS-497/URR for the mini-

indication on the ME-30B/U. Record the

mum setting of the MICROVOLTS control

indication on the corresponding db scale.

that will deactivate the squelch (as indi-

d. Turn the modulator switch on the TS-

cated by the lighting of the CALL LIGHT

497/URR to OFF. The decrease in db as

lamp). The MICROVOLTS SETTING must

indicated on the ME-30B/U must be not

not exceed 3 microvolt.

less than 35 db.

e. Turn the SQUELCH control fully

clockwise (minimum sensitivity). The

150. Receiver Audio Output Test

squelch must deactivate with an input sig-

nal of not less than 25 microvolts nor more

Connect the test equipment to the AN/

VRC-24 or AN/TRC-68 as shown in figure

than 50 microvolt without readjustment of

116. Do not connect the ME-26/U, the AN/

the SQUELCH control.

f. Perform b through e above at test

USM-50, the TS-723A/U, or the AN/URM-

25D.

frequencies of 309.9 and 225.0 mc. The

a. Tune the rt unit and the TS-497/URR

signal

input

required

deactivate

to any convenient frequency.

the squelch must be between 1.5 and 6

b. Set the METER switch to S-METER

microvolt for maximum sensitivity, and

and adjust the TS-497/URR frequency for

between 12.5 and 100 microvolt for mini-

a maximum S-METER indication.

mum sensitivity.

g. Perform b through f above with sup-

c. Adjust the TS-497/URR for a 100-

microvolt rf signal modulated 30 percent

ply voltages of 103 (or 207) and 127 (or

185