Adjusting The Active Bias - Codan NGT 2010 RF Technical & Service Manual

NGT—Checks and adjustments

Adjusting the active bias

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ALTERNATIVE TEXT
NOTE
NOTE
To adjust the active bias:
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184
08-05869 (sheet 2)
The active bias must be set before any intermodulation tests are
performed.
The transceiver must be in Service mode to make this adjustment (see
page 154, Accessing Service
Connect a 50 Ω dummy load to the RF connector ( ) (see
Connect a spectrum analyser via a 47 kΩ resistor to the RF connector (see
Figure 43).
This provides a low-level output for the spectrum analyser.
Select test channel 16.
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
• the 2011 RF Unit via the NGT test handset (see
Set up the spectrum analyser as follows:
Centre frequency
Frequency span
Vertical level
Video bandwidth
Sensitivity
Hold down PTT, then adjust the level of the two tones for compression.
Adjust the two tones displayed on the spectrum analyser for equal amplitude by
adjusting the balance control on the two-tone signal generator.
Adjust the sensitivity control on the spectrum analyser to set the two tones at the top
of the screen.
Adjust the ACT BIAS potentiometer (R241) for a minimum high order (> 9
intermodulation distortion level (see
page 162).
Measure the intermodulation distortion levels relative to each tone.
Add 6 dB to the reading if referenced to PEP (see
specifications for limits).
Release PTT.
or 08-06461 (sheet 2)
mode).
170), or
4.6 MHz
20 kHz (2 kHz per division)
10 dB per division
300 Hz
Depends on the signal level applied to the spectrum
analyser and requires adjustment when transmitting
Figure 31 on page 162
NGT Transceiver System Technical Service Manual
Figure 43 on page
Figure 41 on page 170)
or Figure 32 on
page 39, Transmitter
183).
th
)