Transmit Path; Handset Transmit Path; Rf Unit Transmit Path - Codan NGT 2010 RF Technical & Service Manual

NGT—Brief description (2011/2012)

Transmit path

Handset transmit path

The microphone audio is amplified in the handset and passed to the RF unit via the
handset and speaker connection cable.

RF unit transmit path

Audio & Interconnect PCB (2011)/Audio Interconnect & Data I/O PCB (2012)
The audio from the microphone is buffered on the Audio & Interconnect PCB
(2011)/Audio Interconnect & Data I/O PCB (2012), then passed to the Application
Processor Handset I/F 3 V PCB (2011)/Application Processor Handset & Data I/F PCB
(2012) for compression to convert the signal to a fixed level. This signal is then returned
to the Audio & Interconnect PCB (2011)/Audio Interconnect & Data I/O PCB (2012)
where it is forwarded to the RF/IF PCB.
RF/IF PCB
The audio is mixed with the local oscillator to produce double sideband. It is then filtered
by a 2.5 kHz sideband filter centred on 455 kHz, so that only the wanted sideband is
passed to the first mixer. It is then mixed with the reference oscillator to produce an IF
signal centred on 45 MHz.
The transmit signal is filtered by a BPF with a bandwidth of 15 kHz, before being passed
to the input of the second mixer.
At the second mixer, the signal mixes with the local oscillator VCO to produce the
required channel frequency. The signal is passed to the PA PCB.
PA PCB
On the PA PCB, the signal is amplified then passed through the transmit/receive relay to
the selected LPF.
The output from the LPF is passed via the VSWR detector to the RF output connector.
From there it is connected by coaxial cable to the antenna.
66 NGT Transceiver System Technical Service Manual