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THEORY OF
OPERATION
1.
INTRODUCTION
This
section of the manual provides
a
functional
description of the
SABER
radio. First,
basic
functions
are discussed,
with
each
circuit and its relationship to
other parts of the radio described.
Then, detailed
cir-
cuit descriptions are given
for
each
circuit and module
used
in
the radio.
2.
BASIC FUNCTIONAL DESCRIPTION
a.
DC Voltage Distribution (See
Figure 2)
Operating power
for the radio is derived from
a
7.5-volt
battery.
This 7.5 volts (B+),
is fed,
via
the uni-
versal connector
flex, to
P4,
pins 4 and 6, on the radio
board.
B+
is next routed through 5-amp fuse
F900,
to
pin
11
of
J2.
Then, via
the
PTT/controls flex, B+
is
applied one side
of
the
on/off
switch,
S800. Raw B+
from
the battery (identified on the
schematic
by the
"@®"
symbol) is also applied directly
to
the power
amplifier
(PA),
U202, pins 6 and
12 (vhf) or pins
6 and
8 (uhf).
When the
radio is turned on, the
voltage sources
required to operate the
various
stages
of the radio
are
distributed
as
shown on the main board schematic
diagram
in
the applicable
service
manual.
SWITCHED
B+
from
S800
enters the main radio
board
via interconnect
J2,
pin 4.
From this
point
it
is
distributed throughout the radio to most of the
ICs,
to
OPTION
B+
on
the universal connector (through
R433),
to the
display board (via
jack
J1,
pin
4),
to mul-
tifunction
LED CR40
(through
Q405),
and to regulator
U103.
SWITCHED
B+ (source and destination) can be
identified by the "®" symbol. Note that
SWITCHED
B+
is also provided to the emitters of
Q204 (base bias
to
the
PA),
Q1
(which is connected to the 5-volt regulator
contained
within
U100), Q206 (provides
RX
5V),
and
Q203 (provides
TX
5V).
Additionally,
in
the uhf radio,
SWITCHED
B+ is also supplied
to the
collector
of
Q200.
No.1A
REGULATED 5V
(mid-band and vhf radios
only) originates at inductor L5, and is identified by the
"@"
symbol. No.1A
REGULATED 5V
is distributed to
the following
ICs: U101,
pins
1,
18, and 39; U700, pins
1
and 22; and U102,
pin 14.
No.1
REGULATED 5V
(uhf radios only)
originates
at U100,
pin
14, and is identified by the
"@"
symbol.
No.1
REGULATED 5V
is distributed
to
the following
ICs: U101,
pins
1, 18,
and 39; U700, pins
1
and 22;
U102,
pin 14;
U301,
pin
4; and U200,
pin 1.
No.2
REGULATED
5V,
identified by the "@"
sym-
bol, is provided by regulator
U103
(pin
2).
This voltage
is distributed
to
various circuits
and
ICs
within the
radio, including pins
2, 4, 19, 28, 29, 32, and 64
of
microcomputer U400, and pin 7 of
jack
J2.
TX
5V, identified by the
"©"
symbol, is provided by
U201's
internal
TX/RX
5V
regulator.
This voltage
is
the internal microphone biasing, the temperature-
sensing
circuit of
PA
U202, and (uhf radios only) the
base
of
Q200.
distributed to many of the transmitter circuits, including
BOARD
i
i
i
@
i
Fuse
OFF
ALG
!
SV REGS
t
1
1
vy'
@
-
swe
U100
>
R60
@
ANAREGSV(VHF)
=
MAEPF-19701-A
@
-
#2REGSV
@©
-
mv
ONLY
|
@
#18REG5V(VHF)
|
une!
a
a
i
MAIN
CIRCUIT
U201
TRANSMIT
+
INTERCONNECT
DISPLAY
CIRCUIT BOARD
#1
REG 5V
(UHF)
7
@
AX SV
iow
S
AND
Figure
2.
DC
Voltage Distribution Block Diagram
5
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