Control And Switching; Synthesiser - Codan X-2 Service Manual

Brief Description 2-2
The main elements of the X-2 can be divided into the control and switching
functions, the synthesizers used to produce the oscillator frequencies and the
signal paths taken in receive and transmit modes.
Circuit elements and functions common to both the transmit and receive
paths are the:
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2.2 Control and Switching

The switching and control voltages determine the path taken by the transmit
or receive signals through the transceiver.
Most of the transceiver functions are controlled by microcontroller IC403.
Channel frequencies and options are programmed via the microcontroller to
the Electrical Erasable Programmable Read Only Memory (EEPROM),
IC404. All other transceiver functions are pre-programmed in the
microcontroller's internal Read Only Memory (ROM).
The power on/off and volume controls are hardware functions and not
controlled by the microcontroller.The on/off switch is part of the volume
control and directly energises a power-on relay. A series diode provides
reverse polarity protection.
The volume control in the audio signal path connects the preamplifier (after
the demodulator) and the audio amplifier to drive the loudspeaker.
2.3 Synthesizer
The X-2 transceiver uses single loop synthesizers. The main synthesizer
(VCO1) generates an oscillator frequency of 47 MHz to 63 MHz i.e. 2 MHz
to 18 MHz plus 45 MHz, in 2 kHz steps.
The vernier synthesizer (VCO2) generates oscillator frequencies of
44.5435 MHz to 44.5455 MHz in 10 Hz steps.
The microcontroller IC controls the synthesizers by loading serial data into
both synthesizers. The data varies according to the required channel
frequency programmed into the memory.
When the upper sideband is selected, the X-2 uses one main reference
oscillator of 7304 kHz to produce 456.5 kHz (7304 kHz divided by 16). If
lower sideband is needed, a second crystal of 1814 kHz is used to provide
453.5 kHz (1814 kHz divided by 4).
45 MHz roofing filter
455 kHz sideband filter
local oscillators VCO1 and VCO2
X-2 Technical Service Manual
Publication No: 15-02047