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Beacon

Telemetry transmitter for 145 MHz

The telemetry transmitter for 145 MHz was built entirely with BF200 transistors, of which I had acquired a large batch. There's no reason not to substitute them by some more modern type if there's interest.

The extra complication starting the frequency multiplier chain at 12 MHz, was necessary because of the difficulty of modulating a crystal oscillator.

Circuit

Electrical diagram of the beacon. Some values are missing, but most of those have to be experimentally determined anyway.

Other formats: Postscript, PDF.

The printed circuit board. The 'prototype' had been built cutting islands directly on a board. To maintain the same location of the components, the same layout was respected. Anyway, this is a quite efficient way to construct RF circuits (the image is 300 dpi).
The experimental are (top) was occupied with a microprocessor which digitalized the analog signals, and generated the AX.25 audio signal.

Pintures

First part of the beacon. Left to right: 12 MHz crystal, oscillator transistor. Then follow the first and second frequency multipliers.
'Power' part of the transmitter. Note the thermal plastic drops applied to the coils to assure their form, and to stabilise temperature. The final stage transistor was soldered to the shielding to improve dissipation (not necessary on 'earth').


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(c) John Coppens ON6JC/LW3HAZ mail