Technical description
4-30 HF SSB Transceiver 9323/9360/9390/9780 Technical Service Manual
PA and filters
PTT and PA filter control
1 04-02973 and 04-03096
The drivers, output stages and part of the output bias circuit are permanently
connected to the supply voltage when the Power On relay K8 is energised. They
draw no current until transmit is selected. When the PTT is enabled, power is
supplied via V5 to the remaining circuits of the PA.
The PA LPFs are controlled by the microprocessor IC101 on the Microprocessor
and Audio PCB [1 04-02976 Sheet 1]. Serial data on the local I
2
C bus from the
microprocessor IC101 is applied to IC1 pin 3 (serial data input 8–bit output driver)
on the PA and Filter PCB.
Depending on the channel frequency, the microprocessor IC101 will select one of
the six filters by grounding one of IC1’s outputs (pins 13–18).
When the PTT is selected, the microprocessor IC101 sends serial data to IC1 (on
the PA and Filter PCB), which latches pin 12 to ground. This energises K7
(transmit/receive change over relay) and also forward-biases V5. As a result DC is
provided to the input, pre-driver stages and the 5 V regulator IC2.
The 5 V regulator supplies bias for the ALC and input amplifier. It also enables
the output transistor's bias circuit.
Gain control stage
The RF input from the exciter is terminated by R20 and drives the common base,
long-tail pair V13 and V14. This is achieved through R41 and R44 being
connected in parallel for signal currents. The resistor R43 sets the DC condition of
the long-tail pair and is RF bypassed by C90.
The gain of the input amplifier is controlled by the difference of emitter DC
currents in V13 and V14. The RF input is split between the emitters of V13 and
V14 in inverse proportion to their input impedance. The gain of V14 is reduced
when the ALC increases the current in V13. The collector load of V14 consists of
components L19 and R45. These components are frequency compensating
components and reduce the low frequency gain.
Pre-driver stages
The collector output of V14 is coupled via C94 to the emitter follower V15. The
output of V15 drives the pre driver stage V16. The components R51, L20 and C97
(in the emitter circuit) provide high frequency peaking. The output of V16 is
coupled to the driver stage via transformer T2.
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