NGT—Technical description (2011/2012)
112 NGT Transceiver System Technical Service Manual
Second mixer and exciter output filter
The second mixer IC102 is enabled by applying +10 VTx. This applies DC via R133 to
pin 4, and bias current via R134 to pin 11. The filtered +10 V rail is applied via L116 and
the transformer T106 to the mixer output from pins 3 and 14.
The 45 MHz transmit signal is applied to IC102 pins 12 and 13. It is mixed with the
output of the local oscillator LO1+, LO1– (applied to IC102 pins 5 and 7) to produce the
selected channel frequency at the mixer output pins 3 and 14. The gain of the
mixer/amplifier is approximately 20 dB.
The mixer output goes via a 30 MHz LPF to the transmit exciter output connector J2.
From there it is coupled via a coaxial cable to the PA assembly.
Tuning
When the Tune command is activated, IC408 pin 7 (sheet 3) goes low. This switches off
V413 to allow the 456.5 kHz local oscillator carrier (453.5 kHz for LSB) to be passed to
V206 (sheet 2) via CAR INJ. V206 inserts carrier to the input transformer T202 of the
first Tx mixer IC103 (sheet 1).
At the same time, IC408 pin 5 (Tx MUTE) goes high and switches on V203 (sheet 2).
Thus, IC202/C and IC202/B open the noise gate V204, which stops the inserted carrier
from being loaded by the sideband filter Z201.
The carrier at the output of the second mixer IC102 (sheet 1) is at the frequency of the
selected channel (the SCF). This frequency is used for tuning automatic antennas.
Drawing 04-03378 (sheet 1)
NOTE If the PCB issue status is -06 or earlier, see drawing 04-03378 (sheet 1).
Drawings 04-03378 (sheet 3), 04-03378 (sheet 2) and 04-03378 (sheet 1)
NOTE
If the PCB issue status is -06 or earlier, see drawings 04-03378 (sheet 3),
04-03378 (sheet 2) and 04-03378 (sheet 1).
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