Figure 3-4. Connections for end-to-end with return reference

TM 11-6625-922-15

output signal only at the 75 Ω UNBAL TRANSMIT jack

(1) For operation in the voice-frequency band

(300 Hz to 3,400 Hz), use the 25-Hz modulating

and is usable only in the 50- to 552-kHz frequency

frequency.

range. The 130/135-, 150-, 600-, and 900-ohm positions

(2) Operate the % MOD ADJ control to obtain a

provide an output only at the BAL TRANSMIT jack and

reading of 45 to 50 percent on the dbm/%

are usable only in the 0.1 to 110-kHz frequency range.

MODULATION meter.

Whenever the modulating

frequency is changed, always adjust the % MOD ADJ

Caution: Do not connect the UNBAL

control to maintain the 45- to 50 percent modulation

TRANSMIT or B3AL TRANSMIT jacks

level.

directly to a line having a dc

e. Operate the MOD FREQ ADJ control fully

potential.

Use external coupling

counterclockwise (ccw) and then 5 turns clockwise (cw)

capacitors for isolation.

f. Operate the TRANSMIT FREQUENCY-RECEIVE

FREQUENCY switch to TRANSMIT FREQUENCY.

l. The output signal at either TRANSMIT jack

g. Operate the SWEEP-CARRIER-REFERENCE

cannot be monitored for amplitude by the dbm/%

switch to CARRIER.

MODULATION meter, which reads actual power in dbm

h. Operate the TRANSMIT LEVEL DBM control

into the transmission line load, relative to one milliwatt.

fully cw.

The impedance switching arrangement automatically

i. Operate the COUNTING TIME switch to 1 SEC.

corrects the signal line voltage so that only power is

Operate the % MOD-RECEIVE LEVEL-

read on the dbm/% MODULATION meter.

The

TRANSMIT LEVEL switch to TRANSMIT LEVEL.

frequency of the transmit signal may be monitored by

k. Operate the TRANSMIT IMPEDANCE Ω switch

the FREQUENCY display in Hz. The transmit signal

to the position required to match the impedance (75

level is read by adding the db reading on the

ohm, 130/135, 150, 600, or 900) of the transmission line

TRANSMIT LEVEL DBM switch to the indication on the

to be measured. The 75-ohm position provides an

Figure 3-3. Connections for end-to-end mode.

Figure 3-4. Connections for end-to-end with return reference.

3-6