Am 06.07.2012 09:31, schrieb Johan H. Bodin:
Stefan,
Jim is right as always. Ferrite is unusable in VFO inductors. I just wanted to
add that Micrometals (== Amidon) Txx-6 has a slightly lower temperature
coefficient than Txx-2.
OK, convinced, thanks Johan.
Probably this is why the circuit of W1VD is using a T50-6 as well ;-)
I have built successful VFOs operating directly on 7 and
10 MHz with T50-6 cores. After some work, the drift was low enough to go
unnoticed in a QRP CW rig.
That sounds promising :-)
The inductor, and many other components usually have
a positive temperature coefficient, the QRG falls as the temp' rises.
Yes, CFM, that was happening here too!
One trick
is to use temperature stable capacitors for most of the tank capacitance,
"styroflex" mentioned by Peter is very good if you can find them
I already use them.
, and use
negative tempco ceramic caps (N750, N1500) for a carefully selected portion of
the total capacitance. In todays world of microchips, I find it fun, educational
and rewarding to experiment with an analog VFO :-)
Others would call it "outdated", yes ;-)
73
Johan SM6LKM
73, Stefan/DK7FC
James Moritz wrote:
I suggest using a Txx-2 iron dust core insted of the -43 ferrite.
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