Signal Paths

TM 11-6625-467-34

is discussed in paragraphs 2-3 through 2-18 in terms

power supply has a current rating of 8 amperes.

of other circuits that are used and in terms of the

This voltage is accessible at the. EXTERNAL termi-

CIRCUIT SELECTOR switches responsible for pro-

nals on the test set and can be used to furnish power

g r a m i n g the desired circuit into the test routine.

for a complete Radio Set AN/ARC-54.

d. Frequency Measuring Circuits. The test set

Tables 2-1 through 2-8 show the signal paths for

contains circuits for measuring and adjusting the

each CIRCUIT SELECTOR program specified in

150 Hz and 500 kHz oscillators in the AN/ARC-54.

the operating procedures and self-tests of TM 11-

Both circuits consist of selective amplifiers that are

6625-467-12. `These tables should prove helpful not

tuned to the frequency to be measured. A sample of

only in understanding how the test set operates but

the oscillator output is applied to the selective am-

also in troubleshooting the test set.

plifier, and the selective amplifier output connects

2-3. FREQUENCY SELECTOR-MC Switches

to the ac voltmeter circuit. The oscillator is then

Signal Paths

tuned for a maximum reading on the TEST METER.

(fig. 2-1)

The 500 kHz selective amplifier has, in addition to a

crystal filter, a bandpass filter. With a calibrated

T h e AN/ARC-54 tuning system is composed of

signal level input, the circuit will yield a known out-

three five-wire re-entrant systems, one for .05

put level for all frequencies within the bandpass of

megahertz tuning and two for whole-megahertz

the filter. When used in this mode, the circuit acts

tuning. Switches S7, S8, and S9 in the test set gen-

as a go-no-go tester.

e r a t e codes that tune the AN/ARC-54 RF sub-

e. Diode Switch Circuits. The diode switch cir-

chassis to any desired frequency in the range of

cuits are used to test the homer module. The diode

30.00 to 69.95 megahertz in steps of .05 megahertz.

switches are driven by the 100 Hz oscillator in the

Switches S7 and S8 select the whole megahertz

homer module. By application of gating signals to

frequency and switch S9 selects the .05 megahertz

the switch circuits, both homer left and homer right

increments. Switch S9 generates a different ground

signals are simulated.

sequence on the .05 megahertz select lines for each

f. Loads. The test set provides loads for the AN/

of 20 switch positions. (See table 2-9 for the ground-

ARC-54 power supply and power amplifier modules.

ing sequence. ) Switch S8 generates two separate

Loads are necessary for testing the modules under

coded sequences to select whole megahertz fre-

simulated operating conditions.

quencies in the range of 30 to 69 megahertz. (See

g. Terminating Impedances and Bias Voltages.

table 2-10 for the grounding sequence.) Coding for

The AN/ARC-54 modules are tested individually on

the 30 megahertz range is identical with the coding

the test set. The input and output impedances that

for the 50 megahertz range; also the code for the 40

the module normally connects to during operation

and 60 megahertz ranges are the same. Switch sec-

are simulated by resistors, and capacitors in the test

tions S8B and S8D generate the code for the 40 and

set. Bias voltages, including age (automatic gain

60 megahertz ranges. Switch S7 selects one of the

control), are also provided.

two codes and generates an ambiguity code that

distinguishes the 30 megahertz code from the 50

2-2. Signal Paths

megahertz code or the 40 megahertz code from the

60 megahertz code. Switch S8E generates a coded

The test set consists of many different individual

ground to distinguish the odd and even megahertz

circuits such as oscillators, amplifiers, detectors,

frequencies.

a n d discriminators; e a c h p e r f o r m s a distinct

function. Some of the circuits produce test signals

2-4. Voltmeter Signal Paths

for application to an AN/ARC-54 module; others

(fig. 2-2)

are connected as ac or dc voltmeters for measuring

Oscillator output levels, module output levels, and

module output voltages. Because all functional cir-

various other ac and dc voltages are measured by

cuits in the test set are not used at one time, and

the voltmeter in the test set. Figure 2-2 illustrates

many are used to perform tests on more than one

how ac voltages (150 Hz to 500 kHz), radio fre-

module, the test set provides a means to program

quency voltages (3 to 70 MHz), and dc voltages are

the functional circuits. The programing is accom-

measured. The types of voltage measurement are

plished by four 10-position rotary switches marked

discussed below.

CIRCUIT SELECTOR A,B,C, AND D. The inputs

a. Ac Voltage Measurements. Ac voltages in the

and outputs of both the module circuits and the

test set within the frequency range of 150 Hz to

functional circuits connect to the CIRCUIT SELEC-

500 kHz are measured as shown in A, figure 2-2.

TOR switches. The switches perform like a switch-

The ac voltages to be measured connect to CIRCUIT

b o a r d , connecting the test circuits to various

SELECTOR switches B and C which select the de-

module circuits for testing. Each functional circuit

2-2