NGT—Technical description (2011/2012)
110 NGT Transceiver System Technical Service Manual
RF unit—Application Processor Handset I/F 3 V PCB (2011)/Application
Processor Handset & Data I/F PCB (2012) transmit path
The transmit audio goes to IC7 pin 2. This audio interface device contains an ADC and a
DAC.
The analog transmit audio is sampled and converted by IC7 into digital format. A
compression function is applied to the digital audio as shown in Figure 21 below.
Figure 21: Representation of compression function by IC7
The decay time constant is controlled by firmware and can be varied depending on the
type of transmission. For example, for speech, the time constant needs to be short, but for
data it needs to be lengthened to improve the BER.
The DAC outputs of IC7 pins 8 and 9 are summed together in IC8/A to produce an
output of 1 V p–p. This output then goes via the Audio & Interconnect PCB
(2011)/Audio Interconnect & Data I/O PCB (2012) to the RF/IF PCB.
The output level, which is controlled by firmware, is halved when AM is transmitted or
low power is selected.
RF unit—RF/IF PCB transmit path
Transmit/Receive switching
The PTT command from the handset causes IC408 to drive pins 12 and 13 (Rx Switch
and Tx Switch). This switches off V415 and V416 and switches on V417 and V418, thus
causing +10 VTx to be active. This switches all circuits to the Transmit mode.
2011: Drawing 04-03424 (sheet 1)
2012: Drawing 04-03498 (sheet 1) and 04-03498 (sheet 2)
Drawing 04-03378 (sheet 3)
NOTE If the PCB issue status is -06 or earlier, see drawing 04-03378 (sheet 3).
Input Level
Output Level
1 V
200 mV 2 V
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