KF7IYP - Mike

Sonoita, AZ

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The complete Command Set station covering 3 bands: 160, 80, and 40 meters. Receiver utilizes a BC-453 as a tunable IF with 3 HF Command Set receivers modified for use as tunable converters, each having a 6AC7 RF amp and 6K8 mixer stages. The coils for the local oscillator in each converter have been re-wound to provide an IF freq. output of 470 KHz for the input to the tunable IF. The bandspread has been increased to cover most of the tuning dial for the given amateur band. Additionally, the chassis for each converter has been shortened to remove the unused portion and to provide increased mechanical rigidity, and a 3 receiver rack holds the units during operation. The BC-453 has the addition of an RF gain control, AVC-MVC-CW switch, ANL switch, and solid state audio section.

A Navy CBY-52232 ATA transmitter is used for the 160 meter band after having the freq. coverage altered to cover 1800-2000 KHz. The 80/75 meter band is handled by a BC-457-A after similar alteration to cover 3500-4000 KHz.  A BC-459-A completes the trio for 40 meter duty.

 All 3 transmitters have the addition of a 12A6 buffer stage between the 1626 VFO and the paralleled 1625 PA stages. The plate circuit of the 12A6 is broadband tuned using a slug-tuned coil and provides 7-8 mA drive to the 1625 grids. Screen grid modulation is provided by a TDA-2030 audio power IC through a reverse-connected 10K P-P to multi-tap voice coil universal output transformer. A Shure Unidyne dynamic cardioid microphone sends balanced low-Z audio to the solid state mic preamp. A Heathkit IM-4100 frequency counter rounds out the set-up.

The entire station is powered by 12V deep cycle batteries charged by solar panels. Transmitter B+ voltages are delivered by a Heathkit HP-10 transistorized mobile power supply with 550V under load to the 1625 plates and 210V for VFO and driver. Final amplifier plate current averages 85 mA for about 45W carrier input power. For receiver B+, a small DC to DC converter provides 100VDC with current draw about 28 mA. Total filament current draw is 2.25A and transmit current is 13A for a grand total of 15.25A at 12VDC.

Two antennas are used here at KF7IYP, both being of the end-fed sloping variety. One is 260' long and is primarily used for 160 meters. The other is 130' long and covers the 80/75 and 40 meter bands, with provision for future 20 meter operation. The variometer-style coupling links in the transmitter PA tank circuits feed RG-6 75 ohm coax cable to L-network couplers, one for each antenna, and provide multi-band operation for both. Transmit-receive switching is done by a BC-442 antenna relay converted to 12V for the 130' antenna, and a ceramic insulated DPDT 12V relay on the 260 footer.

When I'm feeling lazy or need to conserve battery power, or both, I fire up my Icom IC-720A solid state HF transceiver and relax for some casual amateur activity....  Michael, KF7IYP

CLICK HERE for Original Photo (2300x1700, ~900K)

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