NGT—Checks and adjustments
NGT Transceiver System Technical Service Manual 183
Figure 43: Setup for adjusting the bias gain
1 Select test channel 28.
1 Connect the signal generator to provide two-tone audio (700 Hz and 2300 Hz) via
the test unit to:
• the audio input on the 15-way GPIO connector on the junction box or 2012 RF
Unit (see Figure 40 on page 170), or
• the 2011 RF Unit via the NGT test handset (see Figure 41 on page 170)
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 Adjust the GAIN potentiometer (R244) for a minimum intermodulation distortion
level (see Figure 30 on page 161).
1 Measure the intermodulation distortion levels relative to each tone.
Add 6 dB to the reading if referenced to PEP (see page 39, Transmitter
specifications for limits).
1 Release PTT.
Centre frequency 24.9 MHz
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
Signal
generator
Spectrum
analyser
50 W load
Transceiver
47 kW
Test
equipment
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