Section II. FUNCTIONAL BLOCK DESCRIPTION

TM 11-5820-919-12

SECTION II

FUNCTIONAL BLOCK DESCRIPTION

3-17. GENERAL.

match standard data systems.

3-18. This section contains a functional block description

of the seven modules within the radio set.

3-23.

Sideband Selection.

Either low or upper

sideband operation can be selected by placing the SB

NOTE

switch in LSB or USB, respectively. The resultant

Although

the

modules

are

not

Sideband Select signal from the SB switch causes the

replaceable

organizational

synthesizer to route either 70 MHz (USB) or 80 MHz

maintenance level, this description is

(LSB) to the modulator/demodulator.

provided to help better understand the

operation of the radio set.

3-24. Volume Control. The VOLUME OFF/MAX

control is a conventional on-off switch and potentiometer

3-19. CONTROL PANEL (Figure 3-3). The control

combination. The on-off switch connects +28v On to the

panel is a removable module which contains all of the

modules in the radio set. The potentiometer controls the

operational controls, and the audio interface connectors

level of audio signals input to the audio amplifier in the

and filters for the radio set. The operational controls and

modulator/demodulator.

audio filtering are discussed below.

3-25. Panel Illumination. The LIGHT switch, when

3-20. Frequency Selection. Selection of the operating

pressed, illuminates the FREQUENCY-KHZ readouts on

frequency is accomplished by setting the six

the control panel with red light.

FREQUENCY-KHZ pushbutton switches to the desired

frequency (2.0000 thru 29.9999 MHz). The resultant

3-26. Audio Filtering. The Audio to or from the audio

binary-coded decimal (BCD) Frequency Select and Filter

devices is filtered both in receive and transmit modes.

Select signals are used to establish frequency control of

This prevents Xmt RF from being picked up by the

the radio set. Frequency selection is performed in 10-

cables leading to the audio devices and being sent back

MHz, I-MHz, 100-kHz,

10-kHz, l-kHz and 100-Hz

into the radio set.

increments.

3-27. POWER SUPPLY (Figure 3-4). The power

3-21. Operational Mode. The MODE switch selects

supply converts +28v On from the control panel to +12.5

one of the following four modes of operation: V-RCV --

and +6.5v.

This is done by two down switchers

Voice and cw receive only

(transistorized regulating circuits). An overload latch

shuts the down switchers off if an excessive load (a short

V-TB -

Voice and cw key transmit/receive

circuit, for example) is present at the output. The +6.5v

V-TR -

Data transmit/receive

goes to the antenna tuner, power amplifier,

V-RCV-

Data receive only

modulator/demodulator, and synthesizer. The +12.5v

goes to the control panel, synthesizer, and modulator/

3-22. The Mode Select signals from the MODE switch

demodulator. These voltages are regulated.

are routed to the modulator/demodulator to activate solid

state switches which place the radio set in the selected

3-28. SYNTHESIZER (Figure 3-5). The synthesizer

operating mode. In V-RCV mode, the radio set operates

generates three sinusoidal LO signals which are used by

as a receiver only with the modulator (transmit) inhibited.

the modulator/demodulator.

All of the frequencies

In the V-TR mode, either transmit or receive operations

generated by the synthesizer are referenced to a

are possible using voice or cw signals. Pushing the PTT

temperature-compensated crystal oscillator (TCXO),

on the handset or pressing the cw telegrapher's key

which is the frequency standard for the radio set.

sends a Xmt Enable to the modulator/demodulator,

Because the TCXO is temperature-compensated over a

which puts the radio in transmit mode. The same

-46 to +71 C range, the Xmt RB" frequency will not

features (receive only, transmit/receive) are available for

data D-TR and D-RCV communication, except that the

signal bypasses the volume control, the output level

becomes fixed, and the input impedance is increased to

3-5