NGT—Checks and adjustments
188 NGT Transceiver System Technical Service Manual
1 Set up the spectrum analyser as follows:
1 Hold down PTT, then adjust the level of the two tones for compression.
1 Adjust the two tones displayed on the spectrum analyser for equal amplitude by
adjusting the balance control on the two-tone signal generator.
1 Adjust the sensitivity control on the spectrum analyser to set the two tones at the top
of the screen.
1 Measure the IMD levels relative to each tone.
Add 6 dB to the reading if referenced to PEP (see page 39, Transmitter
specifications for limits).
If IMD is outside of the specified limits, further analysis is required.
1 Release PTT.
1 Check the IMD on the remaining frequencies (see Table 46 on page 156).
Centre frequency Set to frequency of selected test channel
Frequency span 20 kHz (2 kHz per division)
Vertical level 10 dB per division
Video bandwidth 300 Hz
Sensitivity Depends on the signal level applied to the spectrum
analyser and requires adjustment when transmitting
NOTE
The centre frequency of the spectrum analyser must be set to the
channel frequency selected.
NOTE
To check for spurious and harmonic components during the IMD
checks, adjust the frequency span of the spectrum analyser.
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