8525B/8528 Technical Service Manual Brief Description 3-3
Publication No: 15-02036 Issue 6
3.5 Display, Control and Switching
All the transceiver functions are microprocessor controlled with the required
channel frequencies, facilities, etc being preprogrammed into an Erasable
Programmable Read Only Memory (EPROM).
The front-panel and extended (8530, 8532 or 8531S) control head displays,
and switch-pads are controlled via a four-wire serial bus.
Other functions such as filter switching, PTT and tone generation are
controlled either by buffered microprocessor signals or the relay-switched
‘C’ and ‘D’ supply voltages. The microprocessor switches the associated
relay (K1 on the Motherboard), depending on the transceiver mode. The
relay is energised during transmit and de-energised in receive.
3.6 External Power Amplifiers
In suffix H transceivers, the PA is replaced by a PA Exciter Interface
Assembly to drive an external PA assembly. The transceiver is powered
from the external PA.
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