High power—Technical description
NGT Transceiver System Technical Service Manual 229
Filter PCB
The filter assembly removes harmonics from the combined amplifier output. There are
seven filter banks. Each filter bank has two relays switching the input and output of a
7-pole elliptic filter.
The output from the filter is fed to the amplifier output connector via the ALC/PTT
Switch PCB.
Control PCB
The Control PCB has a number of functions:
• A microprocessor for filter band selection and fault monitoring and reporting.
• Fault detection and latching circuitry for amplifier protection. The faults that are
monitored include:
• power supply overvoltage (IC105/A)
• power supply undervoltage (IC105/B)
• loss of amplifier bias (IC106/B)
• heatsink temperature over 70°C (158°F) (IC109/A)
• load VSWR in excess of approximately 3:1 (IC202/A)
• low gain of the amplifier (IC202/B)
• excessive ALC voltage (IC205/A)
• amplifier internal unbalance (IC207/A)
In the event of a fault, the fault state is latched, and the amplifier bypassed by
disabling PTT.
• Temperature-based fan control. The fans operate at low speed when the heatsink
temperature exceeds 45°C (113°F) and at high speed when the temperature exceeds
55°C (131°F).
• ALC control for connection back to the NGT. ALC voltage is generated based on
peak output power, average output power, reflected output power and output
transistor collector swing. There are LEDs on the Control PCB that indicate which
of the ALC signals is controlling the output power level.
• Front panel indicator control. The front panel indicators show VSWR and
overtemperature faults. A combination of all other monitored faults are indicated
with the single Fault indicator. There is also a bar graph meter, which shows either
amplifier PEP or current drain depending on the position of the meter switch.
Drawing 04-03415
Drawing 04-03418 (sheet 1) and 04-03418 (sheet 2)
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