ALS-1306 Functional Overview
The ALS-1306 is an amateur radio multiband radio frequency linear power amplifier. This device requires
certification. This device complies with technical standards of CFR Title 47 part 97.317(a) and (b) as of April
2013.
General Operation
This linear amplifier covers the 160, 80, 40, 30, 20, 17, 15, 12, 10, and 6-meter amateur bands. Up to 100-watts
exciter power is applied to relay RLY1 on circuit board RLY. With the main power OFF, the
STANDBY/OPERATE switch on STANDBY, with a fault warning LED illuminated, or with the rear panel
RELAY jack ungrounded, RLY1 bypasses through RLY2 directly to the antenna port.
When power is ON, the STANDBY/OPERATE switch in the operate position, and the rear panel RELAY
control line held low (below 1 volt), exciter power is routed through RLY1 to the PD8 power divider board.
Power Division
The PD8 power divider board attenuates the exciter input signal, and divides exciter power equally, between
two 600-watt power amplifier modules. It is 50-ohms on all three ports, with 8.2 dB nominal attenuation to each
output port.
The PD8 circuit board consists of a conventional magic-T power divider, components T2 and R7. This T
divides drive power into two equal-power signals. Each signal path has a 5 dB attenuator consisting of high
power resistors R1 through R6. The 5 dB attenuators on each output port terminate the T in 50-ohms and
provide an additional 10 dB of input port isolation between the two PAM’s. With a 50-ohm source, in excess of
30 dB port-to-port isolation occurs between PAM inputs. A minimum of 16 dB isolation occurs regardless of
input port termination. The attenuators also work in concert with the magic-T to provide a 50-ohm input
termination for each PAM. The 50-ohm termination and input port isolation results in unconditionally stable
PAM’s.
PAM-606 (power amplifier modules)
Power amplification comes from two 600-watt power amplifier modules. Each PA module (PAM-606) uses
four MFR-150 field effect transistors. Each MRF-150 has 100 mA to 300 mA quiescent current. Transistor
conduction angle is slightly over 180-degrees, providing linear class-AB operation. While the precise value of
quiescent current has little effect on linearity, it is very important to adjust all eight FET’s to the same quiescent
current. Target current is typically 150 mA in this design. Normal dc drain operating voltage is approximately
50-volts. Be aware bias control rotation is reversed in CB2 boards, as compared to the previous generation
ALS-1300’s CB1. When servicing any solid state PA, always verify function of bias and set for minimum bias
before applying drain voltage.
Unlike standard Motorola based modules, the PAM-606 modules use two diametrically opposed push-pull pairs
of 150-watt MOSFET’s. The 300-watt push-pull pairs drive balanced VHF striplines. The balanced striplines
combine at a matching transformer. The linear RF power FET’s mount on a forced-air-cooled aluminum
heatsink.
Two dc fans cool each PAM-606 module. Two thermistors (PAM-606 R2) sense power amplifier transistor
temperature. Transistor temperature thermistor R2 regulates bias voltage, reducing bias voltage as transistor
temperature increases. This bias feedback system keeps transistor quiescent current stable independent of
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