KF7IYP
- Mike
Sonoita, AZ
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Southern Arizona AM Page
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on Power Supply Failure and Repairs |
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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. A Navy CBY-52232 ATA transmitter is used for the 160 meter band with freq. coverage modified to 1800-2000 KHz. The 80/75 meter band is handled by a BC-457-A modified to cover 3500-4000 KHz and a BC-459-A completes the trio for 40 meter duty. The entire station is powered by 12V deep cycle batteries charged by solar panels. |
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The station control box brings
together the switching and metering functions for the command sets as
well as the microphone preamp and screen modulator circuit
boards. The box was constructed from sheet metal and plywood
found in a roadside ditch. The vintage Heathkit counter monitors
transmitted frequency. Click on photo for hi-res image, or here. |
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This is an inside view of the control box
showing the mic. preamp, power amp
using TDA2030 IC and modulation transformer. Modulation is
applied to the 1625 screens as originally designed. RFC is
necessary to quash power supply switching noise from entering preamp
Vcc. Click on photo for hi-res image, or here. |
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The
old station receiver was a revamped BC-348-Q. It was modified for
double-conversion operation by adding a second mixer driven by a 2nd
local oscillator that uses the 1000 kc crystal from a BC-221
frequency meter. Additional IF selectivity and gain was then provided
by the 85 kc IF strip from a BC-453 LF receiver. It has a 4W
solid-state audio section.
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Next two photos are L-network with Command set
antenna relay. "Scroller" inductor wound on 2" poly pipe, note "knuckle
burner" lead from coil into relay below crank on tuning cap.
Feed-through made from old utility pole insulators and alligator clip
"lightning arrestor". Rat Shack meter nec. for tune-up 'cause RF
ammeter inop- thermocouple apparently kaput. Click on photo for hi-res image, or here. |
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Click on photo for hi-res image, or here. | |
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Click for mp3 file of KF7IYP signal of 24
Oct 10 as heard at K7JEB (860KB) (Rather noisy -- 75-meter band going out in late morning) |
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2-meter
FM is the only 24/7 communication mode available from the KF7IYP QTH,
the surrounding terrain blocking all cellphone and WiFi signals.
The 2-meter antenna system consists of an omni-directional, half-wave
groundplane and a 5-element yagi. The groundplane antenna is
termed "The Big Gulp" from the creative recycling of a beverage
container from the local 7-11 soda fountain as an ultraviolet-ray
shield for the plastic parts of impedance-matching components (shown
below). Click here for larger image |
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The impedance-matching network at the base of the Big Gulp groundplane antenna. |
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