Codan 2110 series, Repair Manual

Page: 39 / 164

Brief description
Manpack Transceiver 2110 series Repair Guide 23
Receive path
Antenna Tuner PCB
The antenna tuner switches the signal received through either the 50

antenna
connector (J2) or the antenna stud to the PA LPF. The signal from the 50

antenna
connector is switched directly. The signal from the antenna stud is connected via a set of
matching components, selected during the tuning process or via the scanning amplifier.
PA & Filter PCB
The receive signal from the Antenna Tuner PCB passes through a PA LPF to the
transmit/receive relays. It is then passed to the Tx/Rx connector on the RF/IF &
Synthesiser PCB.
RF/IF & Synthesiser PCB
From the receiver input, the signal passes via a selectable pre-amplifier V101 to the input
of the first balanced mixer. Here it mixes with the local oscillator VCO to produce an IF
signal centred on 45 MHz.
The 45 MHz signal is filtered using a BPF with a bandwidth of 15 kHz, before being
passed to the second balanced mixer. The signal mixes with the third harmonic
(44.545 MHz) of the reference oscillator to produce an IF signal centred on 455 kHz.
The output of the second mixer passes through a 2.5 kHz sideband filter so that only the
wanted sideband is fed to the high-gain AGC IF amplifier.
The amplified 455 kHz signal is demodulated to produce an audio signal and also to
operate an AGC circuit. This circuit controls the gain of the IF amplifier to prevent
overloading when strong signals are received. It also maintains constant audio output
with changing input levels.
Audio & Control PCB
Analogue receive audio from the RF/IF & Synthesiser PCB passes though the optional
encryptor module (where fitted), then through the codec and DSP on the Audio &
Control PCB. The codec produces separate outputs, which can be either unprocessed
(raw) audio, or enhanced (noise-reduced, volume-controlled) audio, which then passes
via separate, balanced paths to the Front Panel PCB.
Front Panel PCB
Unprocessed (raw) audio from the Audio & Control PCB is typically passed by the Front
Panel PCB to the line output on the 19-way GPIO connector. Enhanced (noise-reduced,
volume-controlled) audio is passed to three separate audio amplifiers on the Front
Panel PCB. These feed the GPIO external speaker output, the military handset earphone,
and the internal speaker. These outputs can be selectively controlled.