Synthesiser Operation; Control And Switching - Codan NGT 2010 RF Technical & Service Manual

NGT—Brief description (2011/2012)

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
rd
3 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 (USB) and 453.5 kHz (LSB) for the Tx MOD
and Rx DEMOD circuits.

Control and switching

Most functions of the transceiver are controlled by microprocessors.
A microprocessor in the handset reads the key strokes entered by the user. The keyed
data is then passed to the RF unit via the differential handset bus. The RF unit sends data
to the handset to update the display over the same bus.
The RF unit contains five microprocessors located on four PCBs. Incoming data first
goes to the main application microprocessor. This microprocessor then commands lower
level microprocessors to carry out the required function.
68 NGT Transceiver System Technical Service Manual