NGT—Technical description (2011/2012)
NGT Transceiver System Technical Service Manual 119
There is an AGC DUMP input to dump any AGC voltage from a high-level signal on a
previously selected channel when the channel is changed. This allows the new channel to
have maximum gain. The dump is achieved by pulling the AGC DUMP control line low
and the AGC FAST/SLOW control line high for a short period when a channel is
changed.
Demodulator
The output of the 455 kHz IF amplifier is passed to the input of a double balanced mixer
IC208. The IF signal is mixed with the local oscillator that is applied to pins 8 and 10 to
produce an audio output at pin 6. The local oscillator operates at 456.5 kHz for USB
operation and 453.5 kHz for LSB.
The audio is then filtered by the LPF comprising IC209 and associated components,
before being passed to the Audio & Interconnect PCB (2011)/Audio Interconnect & Data
I/O PCB (2012).
RF unit—Audio & Interconnect PCB (2011)/Audio Interconnect & Data
I/O PCB (2012) receive path
Rx audio
The Rx audio from the RF/IF PCB passes through the analog switches IC5 and IC14 to
the volume control IC4/C and buffer amplifier U2/B, then to the audio amplifier IC1 for
delivery to the loudspeaker via the Handset LS Audio connections. A sample of the Rx
audio is also sent to the voice mute circuitry (see page 120, Voice mute).
The volume setting is controlled using the 2-wire serial communications from the
Application Processor Handset I/F 3 V PCB (2011)/Application Processor Handset &
Data I/F PCB (2012).
Tone generation
Tones for the audible signals required for key beeps and warning signals at the
loudspeaker are added to the Rx audio before the audio amplifier via volume control
IC4/B. These tones are generated in IC3, which divides the 4 MHz/2 MHz oscillator
provided by Z1, IC16 and IC15, according to the division ratio assigned by the
Application Processor Handset I/F 3 V PCB (2011)/Application Processor Handset &
Data I/F PCB (2012).
Drawing 04-03378 (sheet 2)
NOTE If the PCB issue status is -06 or earlier, see drawing 04-03378 (sheet 2).
2011: Drawing 04-03425
2012: Drawings 04-03499 (sheet 1) and 04-03499 (sheet 2)
2011: Drawing 04-03425
2012: Drawings 04-03499 (sheet 1) and 04-03499 (sheet 2)
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