Brief description
3-6 HF SSB Transceiver 9323/9360/9390/9780 Technical Service Manual
Transmit path
Microprocessor and Audio PCB
The microphone audio is amplified and levelled in the microphone
amplifier/compressor, then fed to a balanced modulator.
Rx/Exciter PCB
When mixed with the local oscillator, the double sideband output of the modulator
is applied to a 2.5 kHz sideband filter centred on 455 kHz, passing only the
wanted sideband to the first mixer. Here it mixes with the local oscillator VCO2 to
produce an IF signal centred on 45 MHz.
The transmit signal is filtered by the 15 kHz wide band-pass filter before being fed
to the input of the second mixer.
At the second mixer, the signal mixes with the output of oscillator VCO1 to
produce the required channel frequency. It passes through a 30 MHz low-pass
filter to the PA and Filter PCB.
PA and Filter PCB
On the PA assembly, the signal is amplified, then it is passed through the
transmit/receive relay to the selected band filter. The output from the filter is fed
via the VSWR detector to the antenna output connector. From here it is connected
by coaxial cable to the antenna.
The VSWR detector monitors the forward and reflected power and controls the
power output of the transmitter. If a high VSWR is detected, the power output is
reduced to protect the PA.
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