Re: A little question...

Michael <michael.setaazul@...>

----- Original Message ----- From: n3ikq

Thanks for the "back story" Michael. Sounds like your iron spends plenty of time in the "on"
position"! It appears that the front end of the SI series chips has varicaps built in which means
simply adding an external ferrite forms the resonate tank. Other radio chips aren't designed that
way so you have to feed them with your own highly pre - selected signal. Am I on the right track?
Just trying to keep up and understand!

Yes, the "clever chips" autotune the external L (a bit like the principle of AFC in FM radios, but
with much wider range, of course). The L has to match fairly well so as to stay in range of the
internal varicap. If the internal ferrite L is replaced with a bigger external one a little
experimenting may be required. The SONY SRF-59 is a good radio to start tinkering with as it is
more basic - and cheap to replace if the soldering iron slips :-)


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