output produced by each buffered VCO is sufficient to drive the synthesizer frequency divider
and the other following circuits, (mixer for the receiver and the transmitter power amplifier).
The VCO and buffer stages for both transmit and receive oscillators, are housed in separate
screened compartments which are provided by the diecast radio screen. In this way a very
high immunity to microphony is assured.
3.2.4 Central Control
Refer to figure 3.9.
3.2.4.1 GENERAL
Refer to the simplified block diagram figure 3.1 and also to circuit diagram for detailed
description. The PRM80 central control consists of a dedicated single chip microprocessor
IC206. This device supervises all functions of the transceiver as well as providing the
analogue selective call encode and decode. The microprocessor is located on the control
printed circuit board, in conjunction with the associated power supply and peripheral circuits.
Interface between the microprocessor and the controlled functions is via a bi-directional serial
data bus. The nature of this data control is such that the bus is inactive unless a specific
action is required, eg. re-program synthesizer, change display information, etc. To effect
control via the serial bus, the integrated circuit under control is enabled during the period of
the data burst.
All the operational characteristics of the software are fixed in the masked program memory
within the microprocessor. The external EEPROM is required to provide the microprocessor
with information on which software options are to be enabled from the many configurations
available.
3.2.4.2
POWER SUPPLY
The radio transceiver uses five supply voltages in all, four of which are provided as regulated
voltages. The supply voltages are:
+13.8V unregulated
+5.2V regulated (switched)
+5V regulated (un-switched)
+9V regulated (switched)
+23V regulated (switched)
The unreg13.8V supply connects permanently to the transmitter power transistors
TR421 and TR422, and also to the receiver audio power amplifier IC202. This primary supply
voltage is filtered by L205 and C285, C286. A high power Zener diode, D217, provides for
suppression of voltage spikes and reverse polarity protection.
The +5.2V regulated supply operates all the logic controlled integrated circuits. The +9V
regulated supply operates the majority of the radio and audio analogue circuitry. The +23V
supply is used to power the synthesizer loop filter OP AMP and the front end tracking circuit.
Section 3 Page 17