TRANSMllTER SIGNAL FLOW-continued

TM 11-5820-670-30

1-33. TRANSMllTER SIGNAL FLOW. (CONT)

Buffer amplifier A6400 also applies audio modulated signals to isolation amplifier A6600 (18) and then

to mixer A1400 (19). The isolation amplifier assures that buffer amplifier (10) output signals are

injected into the mixer, but local oscillator signals are not injected back into the buffer amplifier to

cause spurious outputs.

Master oscillator signals originating in A6300 (9) are combined in mixer A1400 (19) with those

originating in local oscillator A1500 (22) which is kept at correct frequency by crs (21). The mixing

process produces an 11.5 MHz signal which is amplified by first and second if. amplifiers A8300 (20)

and then applied to the phase discriminator (7) to be compared with the 11.5 MHz signal from

modulator A8100 (6). The phase discriminator then produces a correction voltage that is applied to

master oscillator A6300.

The audio modulated signal from buffer amplifier A6400 (10) is applied to rf drivers (11) and rf

amplifiers (12) for amplification, then fed to rf detector (13). The rf detector is a directional coupler

circuit which samples the forward and reflected power components of the rf output signal. The

rectified output of the detector is applied to agc amplifier (14). The agc amplifier controls the gain of

the transmitted power by increasing or decreasing the signal to rf drivers (11). Increasing the gain

from the agc amplifier causes less power radiated through the antenna. Decreased gain from the agc

amplifier causes higher power radiated through the antenna. The agc amplifier controls the gain in the

one to ten watt range. Fm rf power from rf detector A6500 is applied through relay K4504 to band-pass

filter FL4501 (15A) or (15 B). Pressing the push to talk button energizes relay K4501 which puts the

radio set in the transmit mode. Band-pass filter FL4501 attenuates harmonics in either the

band,

band, 53 MHz 75.95 MHz, depending on the frequency of the

30 MHz 52.95 MHz, or the

transmitted power.

Transmitted power is applied from filter FL4501 through relay K4501 to side tone gate detector A4500

(16). The sidetone gate detector outputs a ground signal which energizes relay K5502 for the purpose

of activating audio amplifier A5400 (27). A ground signal from the sidetone gate detector will not be

produced to unsquelch the audio amplifier until the power level being transmitted is 0.6 watt or

greater. The rf modulated power is also coupled to reflectometer A4500 (17).

When transmitted power reaches at least 0.6 watt, two diode circuits in the reflectometer are

activated. One circuit detects forward power and the other detects reflected power. When the test

switch on the radio set is in the forward position, current flows through the forward detector and into

the TEST METER. When the switch is in the reflected position, current flows through the reflected

detector and into the TEST METER to be monitored. Most of the rf power entering the reflectometer is

coupled to the antenna to be radiated.

In order for the radio set operator to hear what he is transmitting, the transmitted audio is applied to

the receive circuits. The audio modulated 11.5 MHz if. from mixer A1400 (19) is applied through if.

attenuator (23) (no attenuation occurs) to first and second if. amplifiers A4100 (24) for

amplification. If. is again amplified in third and fourth if. amplifiers of A4200 (25). The hunt cutoff

detector located in A4200 is used to rectify the signal and supply a dc bias voltage to hunt generator

A8400 (8).

Unmodulated audio intelligence from discriminator A4200 (25) is applied to audio squelch preamp

A4300 (26) for initial amplification. The audio from A4300 is applied to audio amplifier A5400 (27) for

further amplification. The sidetone gate signal from A4500 (16) allows application of the +16 vdc to

the audio amplifier for unsquelching. When unsquelched, the audio intelligence is amplified in the

audio amplifier and coupled to interphone amplifier (2) to be heard in earphone (1).

1-32