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22nd March 2009 12:13
Alan your beacon is +20 dB over S9 in Manly.... as you may have known..
cheers
Patrick
11th August 2008 11:02
John,
You read my mind, I was planning on varactor fine-tuning as I didn't want to have open holes in the oven. Hopefully the only insulation penetrations will be a few feed-thru lines and the RF out.
I didn't consider using variable DC drive to a varactor for FSK width adjustment, but that's an excellent idea - Thanks. It also allows MT-hell style modulations and in general more flexibility. Currently it is just a diode switch, and there is some odd edge overshoot that I suspect is related to the microcontroller drive limiting (it is also driving LEDs) or RF rectification effects.
Once I get it all nice and stable I'll announce it on the Knights list.
Regards,
Alan
11th August 2008 10:50
Alan - nice going!
Once the TX section is in a shielded enclosure
with stable thermal padding it becomes a shame
to have all your centering and FSK shift trims
locked away inside. Access to them disturbs all
the stability.
Consider a varicap (LED) capacitive trimmer and
not a trimmer cap - then a remote pot allows
trimming with zero insulation or mechanical
disturbance of stray C.
It will interact with the fsk shift width slightly.
I use one LED varicap for FSK and a
separate LED varicap as the centre controller.
A 1k or 10k pot on the Tiny13 allows similar
remote "dc" control of the FSK envelope and
hence the width.
John.
22nd March 2009 12:39
Alan Yates wrote...