Chapter 2. FUNCTIONING OF EQUIPMENT - TM-11-6625-467-340011

TM 11-6625-467-34

CHAPTER 2

FUNCTIONING OF EQUIPMENT

Section I. BLOCK DIAGRAM FUNCTIONING

2-1. General Test Set Functioning

for all AN/ARC-54 modules.

(3) The 10 kHz oscillator frequency is above

Test Set, Electronic Circuit Plug-In Unit AN/

the audio response of the AN/ARC-54 and is used to

ARM-87, is composed of a series of 13 plug-in circuit

simulate noise for carrier squelch tests.

c a r d s containing various circuits for testing in-

(4) The 500 kHz oscillator is used to perform

dividual Radio Set AN/ARC-54 modules. Four CIR-

checks on the fixed intermediate frequency (IF)

CUIT SELECTOR switches on the test set front

module. This oscillator is capable of being frequency

panel connect the desired circuits to the module

modulated. Tests on the 500 kHz discriminator are

under test. A TEST METER on the test set front

performed by the use of the oscillator in this mode.

panel provides a visual indication of the module per-

(5) The 3.975 and 5.925 megahertz osculatory

formances, A general description of the various cir-

are used in performing tests on the AN/ARC-54

cuits in the test set and their uses is given below.

variable IF module.

a. Voltmeter Circuits. Several of the test set cir-

(6) The 30 and 68 megahertz oscillators test the

cuits are used in nearly every test performed on the

RF amplifier and power amplifier modules on the

AN/ARC-54 modules. The most extensively used

AN/ARC-54 RF subchassis.

circuit is the audio amplifier/detector. This circuit

( 7 ) As stated above, each oscillator output

is used in conjunction with the TEST METER to

amplitude is variable. The oscillator amplitude con-

p e r f o r m as an electronic alternating current (at)

trols are on the test set front panel. Before an oscil-

voltmeter. Low-level signals in the frequency range

lator is used in the AN/ARC-54 module testing pro-

of 150 hertz ( Hz) to 500 kilohertz (kHz) are con-

cedures, the oscillator output is always connected to

nected to the audio amplifier/detector input. The

a voltmeter circuit (a above) to set the output level

a u d i o amplifier/detector amplifies the low-level

before it is applied to the module circuit. The low

signal, rectifies it, and applies the resulting direct

frequency oscillator outputs are routed through the

current (de) voltage to the TEST METER for read-

C I R C U I T SELECTOR switches. The 3.975 and

o u t . The voltmeter circuit measures ac voltages

5 . 9 2 5 megahertz oscillator and the 30 and 68

both from the modules and from the test set itself.

megahertz oscillator outputs appear at RF connec-

Oscillators in the test set that have variable output

tors on the front panel. RF jumper cables supplied

a m p l i t u d e s are set to the proper output level

with the test set are used to connect these oscillator

through the use of the ac voltmeter circuit. A radio

outputs to the modules and voltmeter circuits.

frequency (RF) amplifier/detector circuit provides a

c. Power Supplies. The test set contains two low

similar arrangement for measuring of 3 to 70 mega-

voltage power supplies and a high voltage power

hertz (MHz). Dc voltages in the modules and the test

supply to furnish operating power to both the test

set are measured by bypassing the amplifiers and

set internal circuits and to the module under test.

a p p l y i n g the dc voltage directly to the TEST

The low voltage power supplies produce negative

METER.

and positive 27.5 volts dc. The high voltage power

b. Oscillators. There are eight oscillator circuits

supply produces +250 and +500 volts dc for oper-

in the test set. Each oscillator produces a single fre-

ation of the AN/ARC-54 power amplifier. All power

quency and has an adjustable output amplitude. The

supply voltages are regulated. The positive 27.5

oscillator outputs connect to the CIRCUIT SELEC-

volt power supply has a special feature that allows

TOR switches which route the oscillator outputs to

the output voltage to be pulsed. The pulse simulates

the desired points. The eight oscillators generate

frequencies of 150 Hz, 1 kHz, 10kHz, 500kHz,

a switching transient and is used to test the despike

circuit in the AN/ARC-54 power supply module.

3.975MHz, 5.925MHz, 30MHz, and 68MHz.

The POWER SELECTOR switch selects the various

(1) The 150 HZ oscillator is used to check the

power supply modes of operation, that is, despike

tone squelch circuits in the receive audio module.

m o d e , high voltage, etc. The positive 27.5 volt

(2) The 1 khz oscillator simulates audio signals

2-1