AR 10052381, Operating And Service Manual

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Model 125W1000A
28 Rev A
3.2.2 A2 Final Dual W-module
The power module is a dual channel RF amplifier module structured around GaN FET dice arranged in a push-
pull configuration. The module operates on a dual supply of VGG = -8V and VDD = +23V, with a VDD draw
of 20.5 amps (10.2 per channel) and VGG draw below 0.15 amps. Power-on sequence is to apply VGG first,
and then VDD, reversing this sequency for power-off. Active closed-loop bias circuits provide for the safe
operation of the amplifier into a wide range of load VSWR, at all prescribed drive levels and frequencies.
Proprietary coupling circuitry provides superior module input and output matching, low distortion, high density,
with best gain and power flatness across the band. The module provides approximately 15 to 17 dB small-signal
gain and better than 10 dB input return loss, with 120 watts average power at 3 dB compression per channel,
over the 80 – 1000 MHz band.
Two fault circuit outputs are provided to indicate (1) RF FET drain current faults, indiscriminately an over- or
under-current of either RF FET assembly, and (2) a thermal fault. Both fault circuits are “open drain” designs,
which pull an external supply (+3.3V with 1 k-ohm series resistance) low, to generate a fault signal. A FET
drain current fault may result from operating the amplifier beyond the prescribed load, drive, or modulation
conditions, or as the result of compromised module components. If certain conditions generate a predictable
fault, those operating conditions should be reviewed to verify they do not violate the safe operating parameters
of the amplifier, such as a high peak power which may violate maximum allowable input power in any signal
with high peak-to-average ratio. It is normal that faults occurring under high drive or load VSWR conditions
may not be repeated in the absence of those conditions, and it is also possible that incorrect configuration or
tuning of the gain structure within an amplifier may generate faults in a properly operating module, by forcing
it behind safe operating limits.
3.3 POWER SUPPLIES (PS1, PS2, PS3)
PS1 is a single output supply. +5V and -15V is fed to the A6 Regulator Assembly. +24VDC is for operating
the cooling fans B1-B3. Primary AC circuit protection is provided by the AC fuses in the Power Entry Module
FL1.
PS2 is a single output supply. The main +27.0 volts DC supplies voltage to the Drain FETs in the A1 Preamp
and A2 Final Amplifier.
PS3 is a multiple output supply. +5V is supplied to the A7 control panel assembly. -15V is supplied to the A6
Regulator Assy. and A1 Preamp Assy.