The extra complication starting the frequency multiplier chain at 12 MHz, was necessary because of the difficulty of modulating a crystal oscillator.
|Electrical diagram of the beacon. Some values are missing, but most of those have to be experimentally determined anyway.|
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.
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|