Technical description
HF SSB Transceiver 9323/9360/9390/9780 Technical Service Manual 4-5
Receiver
Input low-pass filters
1 04-02973 and 04-03096
The receiver input signal is fed through one of six relay-selected, PA Low-Pass
Filters (LPF) K1–K6. The signal is then fed via the transmit/receive relay K7 and
signal clamping diodes D3–D6 to connector J3.
High-pass filters
1 04-02972 and 04-03135 Sheet 1
From J3 on the PA assembly, the High-Pass Filter (HPF) is connected by a coaxial
cable to J2 located on the Rx/Exciter PCB. Six HPFs are used to complete the
band-pass filter (BPF) characteristics. These are diode switched according to the
frequency band in use, by grounding the appropriate select line from IC1. For
broadcast channels below 2 MHz, a 14 dB resistive attenuator is selected instead
of a filter.
This is an example of how the HPF works. If the HPF 2-3.1 is selected, IC1 pin 10
switches from 10 V to 0 V. This completes the input DC switching current path
from the "B" rail via R2, L1, D11, L18 and R14 to 0 V. Diode D11 is forward
biased and passes the receive signal to the input of the selected HPF.
The output DC switching current path from the "B" rail consists of R3, L2, D12,
L20 and R15 to 0 V. With D12 forward biased, the receive signal at the output of
the 2-3.1 HPF can either be fed directly via D15 and C57 to the following 29 MHz
low-pass filter (LPF) or via D16 to the input of the RF amplifier.
RF amplifier
1 04-02972 and 04-03135 Sheet 1
The RF amplifier (consisting of V1 and its associated components) has a nominal
gain of 12 dB. It can be selected from the front panel on the control head. When
the RF amplifier is selected, IC2 pin 12 goes high, switching the output of IC3/A
and B (in parallel) from 0 V to approximately 10 V. This action applies DC volts
via RF filter inductor L27 to the primary of T2, then to the series inductors of the
LPF L26-L24 to the collector of V1. The DC volts also forward biases V1 via
feedback resistor R24.
With the RF amplifier selected, the voltage on the base of V1 is positive with
respect to the output of the HPF network, thus forward biasing D16. This allows
the signal to pass to the input of the RF amplifier. At the same time, D15 is
switched off, as the cathode is held approximately 2 V positive with respect to the
anode.
To Next Page
Loading...
Need help?
General
