Revision 2
22
Push-pull operation, negative feedback, and linear biasing of FETs provide significant pre-filter
harmonic suppression.
2KWF6 Lowpass Filter Assembly
Each PAM-606 module connects directly to the 2KWF6 circuit board assembly through 50-ohm
cables. Each PA module feeds a 50-ohm high power combiner. This combiner isolates the two
PAM-606 inputs while maintaining 50-ohm impedance. Two 25-watt 200-ohm power resistors,
R7 and R8, dissipate power level or phase errors between the PA module inputs. Voltage step-
down transformer T1 senses voltage across combiner dump resistors, R7 and R8. T1 is located
on the 2KWF6 lowpass filter board. This voltage, representing PA combiner unbalance, appears
on the front panel multimeter as a “PAB” (power amplifier balance) indication. PA unbalance
reference voltage also feeds a comparator on the CB2 control board. This comparator disables
the PA in the event the power amplifiers become significantly unbalanced, and illuminates the
PA front panel light.
The output of the high-power combiner enters the filter section through a directional coupler
consisting of current transformer T2, capacitors C36-38, C40-42, and resistors R4, 5 and 6. This
directional coupler detects the power amplifier termination errors. These errors include filter
band errors. A comparator on the CB2 control board monitors directional coupler termination
errors. Any significant filter or antenna reflected power error disables the amplifier. Such errors
normally come from selecting the wrong filter for the exciter’s operating band, or having a poor
load SWR on the amplifier.
The output of the filter board directional coupler routes through one of seven 5-pole lowpass
filter groups. Relays, controlled by CB2 control board logic, select the appropriate lowpass filter
components.
Control and Protection Logic
The CB2 control board contains all protection comparators (U7) and control logic latches (U1).
In the event of an operational fault, U1 locks out the amplifier and illuminates the proper front
panel warning light sequence. CB2 also contains bias, relay sequencing, and fan speed controls.
The CB2 board contains band-decoding systems, and automatically disables operation between
25 and 28 MHz in all ALS-1306 amplifiers regardless of band selection mode. This embedded
logic function cannot be disabled or changed.
SWR
The SWR board is a standard 50-ohm directional coupler. The SWR board samples line current
and line voltage, vector summing line voltage and current before conversion to a dc output
voltage. The resulting voltages represent forward and reflected power, or mismatch from an ideal
50-ohm load.
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