Codan NGT 2010 RF Technical & Service Manual page 536

High power—Brief description
Power amplifier (3061/3062)
The transmitter output from the NGT is connected to the input of the high-power
amplifier. The amplifier is internally bypassed in receive, and when the amplifier is
disabled. Normal NGT operation occurs in these instances. When the amplifier is
enabled and PTT is active, the output transmitted by the NGT is split and delivered to the
Power Amplifier PCB(s) (one PCB in 3061, two PCBs in 3062), then recombined and
filtered before being delivered to the amplifier output.
Monitoring and control of amplifier operation is performed on the Control PCB. This
PCB also provides the front panel indicators.
The raw power supply for the amplifier is provided by a switched mode supply in a
separate unit. This is converted to the minimum possible supply voltage for correct
operation in the amplifier's switched mode active supply (one supply in 3061, two
supplies in 3062) on the Power Supply PCB. This ensures the best possible amplifier
efficiency under all load conditions.
The amplifier power monitoring is provided by a forward and reflected power sensor,
which supplies rectified forward and reflected power envelopes to the Control PCB.
Power Amplifier PCB
Each Power Amplifier PCB contains a single bias supply and two separate amplifiers.
Each amplifier has feedback and impedance correction networks to ensure stable and
consistent gain between amplifiers.
Control PCB
The Control PCB has a number of functions including:
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If a fault is detected and latched, the Control PCB disables the PTT function of the
amplifier, bypassing the amplifier.
Power Supply PCB
The Power Supply PCB is a switchmode DC–DC converter, which takes the raw
70 V DC supply from the power supply unit and efficiently converts it to between 33 and
50 V DC before delivering it to the amplifiers. The power supply is also current and
power limited.
The output voltage is optimised to give the best amplifier efficiency, minimising power
supply requirements.
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switching the band filters
monitoring and latching faults
controlling the cooling fans
generating and conditioning the ALC voltage
controlling the front panel indicators
NGT Transceiver System Technical Service Manual