Technical description
HF SSB Transceiver 9323/9360/9390/9780 Technical Service Manual 4-13
In the first mixer IC8, the 455 kHz transmit signal is mixed with the output of the
local oscillator VCO2. This is applied to pin 5 to produce a second IF output
signal centred on 45 MHz (pins 3 and 14). The gain of the mixer/amplifier is
approximately 20 dB.
45 MHz band-pass filter
The 45 MHz IF signal is filtered through a 15 kHz BPF consisting of T4, Z2, L30,
Z1 and T3. This removes unwanted signals produced by the first mixer. The
filtered output is applied to the balanced input of the second mixer IC5 pins 12
and 13.
Second mixer and exciter output filter
The second mixer IC5 is enabled by operating the transistor switch V3. This
applies DC through R35 to pin 4 and bias current via R38 to pin 11. The filtered
"B" rail is applied via preset resistor R22 and transformer T1 to the mixer output
pin 3 and 14.
The 45 MHz transmit signal is mixed with the output of local oscillator VCO1
then applied to IC5 pin 5 to produce the selected channel frequency at the mixer
output (pins 3 and 14). The gain of the mixer/amplifier is approximately 20 dB.
The balanced network, consisting of components R22, C55 and C56, is adjusted to
remove unwanted spurious signals.
The mixer output is fed via a 29 MHz low-pass filter (consisting of L23, C53,
C51/52, L21 and C50) to the transmit exciter output connector J1. From there it is
coupled via a coaxial cable to the PA assembly.
Tune
When the Tune button is pressed [1 04-02974], a low is applied to the input
port of IC1. The interrupt pin (pin 13) momentarily goes low indicating that the
microprocessor IC2 has to read the input port of IC1. It also detects that the Tune
button has been pressed. The tune command will be sent via the external I
2
C bus
to the microprocessor IC101 on the Microprocessor and Audio PCB [1
04-02976 Sheet 1].
The microprocessor IC101 outputs data on the local I
2
C bus to IC209 on the
Rx/Exciter PCB [1 04-02972 and 04-03135 Sheet 2] to latch output at pin 6
high and pin 10 low.
The high on IC209 pin 6 enables the transmit mixers and disables all of the
receive functions (see page 4-4, Receive/Transmit switching).
To Next Page
Loading...
Need help?
General
