2: System Overview
2-6
PRC1099A-MS
Squelch - U1, U2,
and U3
Receive
Detects low-frequency FM voice
components to actuate squelch.
Input from product detector U4.
Output to squelch gates Q1 and
Q2.
Audio PA - U5
Receive
Amplifies audio for handset or
loudspeaker.
Input from product detector U4
through audio gain control.
Output to handset.
Audio AMP -
U10A
Receive
Provides 0 dBm 600 ohm audio
output.
Input from product detector U4.
Output to Accessory socket.
RF Gate - Q23,
Q24
Transmit
Detects RF output and opens
sidetone gate.
Input from ALC circuitry.
Output to squelch gates.
Squelch Gates -
Q1, Q2
Receive
Switches on Audio PA (U5).
Controls current in RX front end.
Input from squelch control.
Output to Audio PA gate and
gates Mixer board.
CW Hold - Q17
Transmit
Provides semi break-in CW and
ATU tune signal.
Input from CW key and
processor.
Output to tone generator
Processor board.
Filter Switching -
K2–K11
Decodes serial data & selects
correct filter range.
Input serial data from Processor
board.
Output switches RF filters in and
out of transmit and receive path.
ALC - Q21
Transmit
Measures RF current & RF
voltage. Provides 5W and 20W
level output control.
Input from TX PA output.
Output to Sidetone Gate, ALC
gain Mixer board.
T/R Relay - K13
Switches TX/RX RF and R+8V
and T+8V lines.
Input from PTT, Processor board.
Low-Pass
RF Filters
Transmit
Low-pass filters for TX signal.
Input from PA board.
Output to Antenna Tuner board.
Receive
Low-pass filters for RX signal.
Input from Antenna Tuner board
Output to Mixer board through
high-pass filters.
1650 kHz IF Board
1650 kHz Filter -
Y1–Y6
Transmit
Removes a single sideband from
the transmit signal.
Input from TX amp
Output to Mixer board.
Receive
Provides narrowband RX
selectivity.
Input from the Mixer board;
output to RX IF amps.
RX IF Amps - Q1,
Q2
Receive
Amplifies 1650 kHz IF signal.
Input from 1650 kHz filter.
Output to Audio/Filter board.
Table 2-1 Board Functionality (continued)
Function
Path
Description
I/O
