Codan 2110 series, Repair Manual

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Brief description
24 Manpack Transceiver 2110 series Repair Guide
Antenna tuning process
Tuning is an iterative process in which selection of impedance-matching components is
determined by an on-board microcontroller. A frequency-dependent algorithm decides
on a consecutive selection, taking into account the phase and VSWR measurements. The
process is repeated until matching is achieved.
Synthesiser operation
The transceiver uses a single-loop synthesiser. The synthesiser VCO is used as the first
mixer LO, generating an oscillator frequency in 10 Hz steps. In Receive mode, the
frequency of the oscillator ranges from 45.25 MHz to 75 MHz. In Transmit mode, the
frequency of the oscillator ranges from 46.6 MHz to 75 MHz.
The reference oscillator at 14.848333 MHz is fed through a 44.5 MHz BPF to select the
third harmonic to produce the 44.545 MHz second mixer LO. The 14.848333 MHz
frequency is also fed to two DDS ICs to produce a variable reference frequency for VCO
with 10 Hz resolution.
The second DDS IC produces 456.5 kHz for USB and 453.5 kHz for LSB for the
transmit modulator (Tx MOD) and receive demodulator (Rx DEMOD) circuits.
Control and switching
Most functions of the transceiver are controlled by a DSP and microcontrollers. The DSP
reads key strokes entered by the user. Update information is sent to the LCD via a
dedicated bus.
Information exchange between the DSP on the Audio & Control PCB and the PA &
Filter PCB, RF/IF & Synthesiser PCB, and Antenna Tuner PCB is accomplished via four
microcontrollers that share a communications bus. Information exchange between the
Audio & Control PCB and Front Panel PCB is accomplished via a separate dedicated
data bus.