NGT—Checks and adjustments
NGT Transceiver System Technical Service Manual 181
1 Release PTT.
1 Check that the two-tone waveform is clean and undistorted.
If it is not clean and undistorted, further analysis is required.
To adjust the high output power:
1 Select any channel frequency between 4 and 6 MHz.
1 Connect an average or PEP power meter with a 50 Ω dummy load to the RF
connector ( ).
1 Connect an oscilloscope via a 47 kΩ resistor to the antenna connector.
1 Set the oscilloscope timebase to 500 µs per division and the trigger to auto.
1 Connect a 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 Hold down PTT, then adjust the two-tone level for compression.
1 Adjust the Y sensitivity of the oscilloscope for on-screen display and adjust the
trigger for a stationary waveform.
1 Adjust the two-tone balance control for good crossover display.
1 Adjust HI PWR (R32) (see Figure 34 on page 163) for the required output.
Table 48: Power output PEP vs measuring instrument (12/100/125 W)
Power Output PEP 12 W 100 W 125 W
Peak reading meter 12 W 100 W 125 W
RMS reading meter 6 W 50 W 62.5 W
Average reading meter (e.g.
Bird Model 43)
5 W 40.5 W 50.6 W
Oscilloscope 69 V p–p 200 V p–p 224 V p–p
ALTERNATIVE TEXT
Drawing 08-05910 (sheet 1)
NOTE If the PCB issue status is -04 or earlier, see drawing 08-05910 (sheet 1).
NOTE
The transceiver does not have to be in Service mode to make this
adjustment.
NOTE
The output power is factory-set, so it is not likely to be outside the
specified limits. Check that there are no faults with the transmitter circuits
before attempting to adjust the output power.
To Next Page
Loading...
Need help?
General
