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22nd March 2009 12:39

Alan Yates wrote...


Thanks mate. No surprise being so close. :)



22nd March 2009 12:13

Patrick wrote...

Alan your beacon is +20 dB over S9 in Manly.... as you may have known..



11th August 2008 11:02

Alan Yates wrote...


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.



11th August 2008 10:50

John wrote...

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.