PRC1099A-MS
5-1
Chapter 5: Mixer Board
5.1
Circuit Description
The Mixer board includes the first and second frequency conversion mixers. In
transmit mode, the audio modulated 1650 kHz low-level SSB signal is
up-converted to 75 MHz, amplified, filtered, down-converted to the 1.6 to
30 MHz range, and then amplified again to approxi3 dBm.
In receive mode, the receive signal from the Audio/Filter board is up-converted
from the channel frequency to 75 MHz, amplified, filtered, amplified again, and
then down-converted to 1650 (USB) or 1647 (LSB) kHz. The following
sections discuss the components of the block diagram shown in Figure 5-1
below.
Figure 5-1 Mixer Board Block Diagram
to Power Amplifier
Board
AGC
from
Audio/Filter Board
RX
TX
ALC
SYN 2
73.35 MHz
Receive signal
to 1650 kHz
IF Board
12V
SYN 1
76.6 - 105 MHz
1 Hz Steps
TX/RX
Double Balanced
Mixer
Current
Regulator
Squelch
Squelch
Gate
RX Mixer
75 MHz 1650 MHz
30 MHz
LO Pass
Filter
75 MHz
4 Pole XTAL
Filter
Osc.
Buffer
ALC
Amp
TX Amp
1.6 - 30 MHz
TX
75 MHz
IF Amp
RX 75 MHz
IF Amp
First LO
Second LO
RX 75 MHz
IF Amp
Squelch
Gate
Squelch
Osc.
Buffer
Transmit
Receive
Transmit signal
from 1650 kHz
IF Board
T8
R8
T8
R8
75 MHz
75 MHz
1650 kHz
1650 kHz
75 MHz
RX
TX
RX
TX
TX
RX
RX
TX
RX
TX
RX
RX
TX
TX
TX
RX
TX
TX Mixer
75 MHz 1650 MHz
RX IN
TX OUT
1650 KHZ
RX OUT/
TX IN