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|  TM
11-5820-919-40-1
THEORY
OF
OPERATION
the modules within each major unit.
INTRODUCTION.
Finally, a detailed description of each
module is presented.
This chapter describes the radio
This third section
2-2.
First,
can be used in two ways:
(1) by follow-
from a functional viewpoint.
ing the block diagram accompanying the
This
a system viewpoint is discussed.
text, and (2) by referring to the sche-
first section reviews rf mixing princi-
matic diagram of the module found in
ples and automatic impedance-matching
Next,
as they apply to the radio set.
the General Support Maintenance Manual
an overall or major unit viewpoint is
TM 11-5820-919-40-2 as a supplement. The schematic
This second section exam-
discussed.
diagrams shouldbe used when performing trouble-
ines the primary functional role of
shooting procedures on a module.
SECTION
I
SYSTEM
FUNCTIONAL
DESCRIPTION
GENERAL.
Audio, and (2) 5 MHz - Xmt Audio.* The
5-MHz crystal filter passes the 5 MHz -
This section describes the
Xmt Audio (4.999 MHz) and suppresses the
2-4.
frequency conversion and impedance-
5 MHz + Xmt Audio signal.
matching functions of the radio set.
Frequency conversion is discussed in
The output of the 5-MHz crystal
2-8.
filter is then, mixed with 70 MHz if
transmit operation (audio frequency to
upper sideband (USB) is selected on the
radio frequency) and in receive opera-
tion (radio frequency to audio fre-
control panel, or with 80 MHz if lower
sideband (LSB) is selected.
quency).
Impedance-matching is dis-
The mixer
cussed in terms of standing wave ratio
also produces the following signals:
(swr) and the automatic procedure which
the radio set uses.
1.
Upper
sideband
selected
TRANSMIT
OPERATION
a. 70 MHz + 5 MHz - Xmt Audio
(74.999 MHz)*
For ease of explanation, assume
2-6.
the voice signal (Xmt Audio) from the
70 MHz - 5 MHz - Xmt Audio
b.
The Xmt Audio from
(64.999 MHz)
microphone is 1 kHz.
the microphone is routed through the
2.
audio filter which suppresses spurious
Lower
sideband
selected
rf noise signals picked up at the
microphone.
a. 80 MHz - 5 MHz - Xmt Audio
(75.001 MHz)*
The Xmt Audio is then mixed with
2-7.
the 5-MHz local oscillator (LO) signal
from the synthesizer.
The mixer pro-
*Indicates
the
desired
signal
(1) 5MHz + Xmt
duces two signals:
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