Aligning The 455 Khz If And Noise Limiter - Codan NGT 2010 RF Technical & Service Manual

Aligning the 455 kHz IF and noise limiter

Drawing
ALTERNATIVE TEXT
NOTE
NOTE
There are two tuned transformers in the 455 kHz IF circuit located on the RF/IF PCB in
the RF unit. T202 is located in the IF path to the sideband filter. T201 is located at the
output of the noise limiter 455 kHz amplifier.
To align the transformers in the 455 kHz IF circuit on the RF/IF PCB:
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NGT Transceiver System Technical Service Manual
08-05261 (sheet 2)
If the PCB issue status is -06 or earlier, see drawing
The transceiver must be in Service mode to perform this check (see
page 154, Accessing Service
Select any normal receive channel.
Connect a signal generator to the receiver input.
Set the signal generator to 1 kHz above the channel frequency selected (or 1 kHz
below for LSB) at an output of approximately –30 dBm (10 mV).
Fit a link across ON to disable the noise limiter gate (see
Figure 29 on page 161).
Connect an oscilloscope to TP201 using a 10× probe.
Set the input to 50 mV per division (0.5 V per division with the 10× probe).
Set the timebase of the oscilloscope to 50 µs per division.
Set the oscilloscope for an auto trigger.
Adjust T202 for maximum amplitude.
Only a small change in amplitude is seen due to the low Q of the tuned circuit.
Remove the 10× probe from TP201.
Connect a 1× probe to position A (part of the noise limiter links) (see
page 160 and drawing
04-03378 (sheet 1)).
Set the oscilloscope to a sensitivity of 10 mV per division.
Adjust T201 for maximum amplitude.
Remove the link across ON and return it to its parking position (centre).
or 08-05889 (sheet 2)
mode).
04-03106 (sheet 1) or
NGT—Checks and adjustments
08-05889 (sheet
Figure 28 on page 160
Figure 29 on page 161
2).
or
Figure 28 on
and drawing
169