Transmit Path - Codan X-2 Service Manual

Brief Description 2-4

2.5 Transmit Path

Rx/Exciter PCB
The microphone amplifier/compressor IC303/306, amplifies and levels the
audio signal from the microphone and drives a balanced modulator IC301.
When mixed with the local oscillator, the double sideband output of the
modulator feeds a 2.5 kHz sideband filter centred on 455 kHz, passing only
the wanted sideband to the first mixer IC9. Here it mixes with the local
oscillator VCO2 to produce an IF signal of 45 MHz.
The 15 kHz wide roofing filter centred at 45 MHz filters the transmit signal
to remove unwanted mixed signals before it feeds the second mixer.
At the second mixer, the signal mixes with the oscillator VCO1 producing
the required channel frequency (2 MHz to 18 MHz) and passes through a
20 MHz low pass filter to the Power Amplifier & Filter PCB (PA PCB).
PA and Filter PCB
The PA assembly amplifies the signal, passes it on to the transmit/receive
relay, and then to the selected band filter. At the filter output it continues to
the VSWR detector. The detector monitors the forward and reflected power
and controls the power output of the transmitter. If a high VSWR is
detected, the power output reduces to protect the power amplifier.
A coaxial cable connects the signal to the appropriate antenna for
transmission.
X-2 Technical Service Manual
Publication No: 15-02047
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