2: System Overview
2-4
PRC1099A-MS
2.4.6
Audio Outputs Receive Path
The other audio path is routed to the front panel Volume control
potentiometer. This path is also split into two paths: one is routed to the front
panel Audio connector for a handset or headset. The other path is routed to the
600 Ohm output at the front panel Accessory connector for an external loud
speaker.
2.5
Transmit Path
2.5.1
Audio/Filter Board Transmit Path 1
The transmit path begins at a microphone attached to one of the front panel
Audio connectors. From the Audio connector the audio signal is applied to the
VOGAD that automatically adjusts the gain to provide constant audio output
to the balanced modulator. The balanced modulator injects the transmit audio
signal with a 1650 kHz carrier frequency that produces a 1650 kHz,
double-sideband (DBS), suppressed carrier output (1647 kHz for LSB
operation). The modulated DBS transmit signal is routed to the 1650 kHz IF
board.
2.5.2
1650 kHz IF Board Transmit Path
The 1650 kHz DSB signal is routed to the 1650 kHz IF board where it is
applied to an TX IF amplifier and then filtered with a 6-pole, crystal sideband
filter where either the upper or lower sideband is removed. From the crystal
filter, the single sideband (SSB) transmit signal is routed to the Mixer board.
2.5.3
Mixer Board Transmit Path
From the 1650 kHz IF board, the 1650 kHz, SSB, suppressed carrier, transmit
signal is applied to the Mixer board where a balanced mixer combines the
1650 kHz signal with the 73.35 MHz second LO (LO2) from the DDS on the
Synthesizer board to produce a 75 MHz IF signal. This IF signal is amplified
at the 75 MHz amplifier and then applied to the 75 MHz crystal filter.
The 75 MHz IF amplifier has ALC applied that is derived from the currents
and voltages at the transmitter output. The ALC system limits the maximum
current and voltage from the RF power amplifier so that the transceiver can be
safely operated at any VSWR level.
The 75 MHz signal is then down-converted in a double-balanced mixer to the
selected channel frequency. A broadband 1.6 to 30 MHz amplifier increases
the exciter output to approxi3 dBm. A low-pass filter at the output
removes the image frequencies. From the Mixer board, the SSB channel
frequency transmit signal is routed to the Power Amplifier board.