8525B/8528 Technical Service Manual Technical Description 4-29
Publication No: 15-02036 Issue 6
4.10.5 Transmit Amplifier
The RF input to the board is applied to a grounded base amplifier V1. The
DC path for the emitter of V1 is completed via D12 and the C line (0V) on
the RF Mixer and Dual Synthesizer PCB. R6 in the collector circuit of this
transistor provides a range of approximately 6dB of gain control. The signal
from the collector of V1 is passed to an emitter follower V2, the output of
which drives V3. V3 with T1 forms a fixed gain feedback amplifier. The
secondary of T1 is adjusted for 2.0V pp output by preset R6 to drive the
4402 or 4404 PA units.
4.10.6 Receive Circuit
Received RF from the PA unit is applied to the Rx I/P (P3 pins 9 and 10).
The signal passes to the receiver circuits via a broadcast band high-pass
filter formed by L1 to L3 and C1 to C7. Diodes D1 and D2 limit the output
swing of the signal. In the transmit mode the D rail forward biases D2,
clamping the receiver input to ground.
4.10.7 Antenna Control
Lines to control an external antenna or antenna control unit are also taken
through the board for connection to the Antenna Control connector at the
rear of the transceiver. The Scan, Tune and Tuned In control signals are also
taken to and from the PA unit.
4.10.8 PA Unit
Details of the Codan 4402 and 4404 PA Units are given a separate service
manual Code 2037.
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