Linearity Test - TM-11-6625-351-350243

1 , 0 0 0 - or 10,000-microvolt signal

b. Connect the output of the audio oscil-

( a s required) at the SIGNAL IN-

lator (para 100) to the input of audio am-

PUT jack (any frequency).

plifier V701A in the main unit of the test

(3) S e t the variable 5-db step atten-

s e t . A convenient point for injecting the

uator to the 25-db position.

a u d i o oscillator signal is at the unnum-

(4) Rotate the SIGNAL ATTENUATOR

b e r e d feedthrough terminal at the bottom

D B switch to 60 and adjust the

r i g h t corner of the filter box assembly

GAIN control on the tuning unit to

( f i g . 45). This terminal is essentially the

p r o d u c e a 0-db indication on the

same circuit point as terminal Al of con-

main unit panel meter.

n e c t o r J701.

(5) D e c r e a s e the setting of the 5-db

c. Connect Voltmeter, Meter ME-30B/

variable step attenuator in four

U across a 600-ohm, l/2-watt resistor,

steps, from 25- to 5-db, and record

connected from PHONES jack J702 to

the corresponding indication of the

c h a s s i s ground.

d. Adjust the output of the audio oscil-

A N / U R M - 8 5 panel meter.

lator to produce a signal of O l-volt am-

(6) C h e c k the panel meter for a 5-db

1 increase for each step decrease

plitude from terminal Al of J701 to ground.

of the 5-db variable step at-

e. Tune the audio oscillator to 1,000 -

tenuator.

cps and record the voltage indication shown

on the ME-30B/U.

b. CW AVERAGE Test. This test is de-

s i g n e d to check the test set for linearity

f. Repeat procedure e above at the test

f r e q u e n c i e s of 150, 500, 2,000, 3,000,

w h e n a 100-percent modulated cw signal

4 , 0 0 0 , and 5,000-cps. Note the voltage

i s received at the SIGNAL INPUT jack.

reading at each test frequency. The audio

Signal sources capable of producing such

r e s p o n s e curve must be flat, within 8-db

a signal are not readily available. The

following test procedures, when used with

o f the 1,000-cycle value, with a gradual

a n unmodulated cw source, will simulate

s l o p e - o f f at each end. There must be no

the conditions above. For this test, change

r e s o n a n t peaks.

the setting of the function switch to the CW

AVERAGE position.

103. Linearity Test

(1) S e t the tuning unit signal gener-

(fig, 94)

a t o r output level control to pro-

Two tests are required to check the

d u c e a 2,000-microvolt, or a

l i n e a r i t y of the test set; one checks the

2 0 , 0 0 0 -microvolt signal (as re-

linearity in the PULSE PEAK position of

quired) at the SIGNAL INPUT jack.

the function switch, and the other checks

(2) Set the frequency of the tuning unit

t h e linearity in the CW AVERAGE posi-

signal generator and the frequency

t i o n of the function switch. Remove the

dial of the tuning unit under test to

main unit from its instrument case (para 40

a frequency at the high end of the

b, item 12, TM 11-6625-351-12). Set up the

band under test.

equipment as shown in figure 94 and pro-

(3) A d j u s t the GAIN control on the

ceed as follows:

tuning unit to produce a full-

a. Pulse Peak Test. Connect the appli-

scale, 20-db indication on the main

c a b l e tuning unit signal generator (de-

unit panel meter with the variable

pending on the tuning under test) through

5 - d b step attenuator set to the 5-

a 5-db variable step attenuator (para 100),

db position.

o r equivalent, and through the RG-5B/U

(4) P l a c e t h e I F . C A T H O D E F O L -

cable, to the SIGNAL INPUT jack of the

LOWER ADJ switch S704, a chassis

t e s t set.

adjustment control (fig. 51) in its

(1) Set the main unit function switch to

o p e n - c i r c u i t position (check with

the PULSE PEAK position.

a multimeter). Shunt its terminals

with a 250,000-ohm potentiometer.

(2) Set the tuning unit signal generator

Use alligator clips to connect one

o u t p u t level control to produce a

220