High power—Fault finding and adjustments
NGT Transceiver System Technical Service Manual 241
Adjusting the ALC bridge
To adjust the ALC bridge:
1 Connect setup as per page 180, Adjusting high output power.
1 Select any channel near 15 MHz.
1 Attach a load-matching transformer between the load and the amplifier output, so
that the amplifier is presented with a 16.7 Ω load.
1 Hold down PTT.
1 Adjust the capacitor C5 to give 150 W (3061) or 300 W (3062) PEP into the load.
1 Release PTT.
1 Reverse the load-matching transformer to present a 150 Ω load.
1 Hold down PTT, then check that the output power into the load is the same.
1 Release PTT.
1 If necessary, re-adjust the capacitor to give the same power for both load cases.
Adjusting the power supply frequency
To adjust the power supply frequency:
1 Switch off the NGT and remove solder link X1 from the Power Supply PCB in the
power amplifier.
1 Ensure there is no audio drive to the NGT.
1 Hold down PTT.
1 Using a frequency counter on TP1, adjust R17 to give a frequency of 70 kHz
±100 Hz.
1 Using a frequency counter on TP101, adjust R117 to give a frequency of 63 kHz
±100 Hz.
1 Release PTT.
1 Switch off the NGT and resolder link X1.
Drawing 08-05985
NOTE
The transceiver does not have to be in Service mode to perform this
adjustment.
NOTE
The High VSWR LED may illuminate while this adjustment is
made. Switch the transceiver off then on again to reset this LED.
Drawing 08-05978 (sheet 1), 08-05978 (sheet 2) and 08-05978 (sheet 3)
NOTE
The transceiver does not have to be in Service mode to perform this
adjustment.
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