Re: VFO Stability


Date: Mon Aug 07 1995 - 16:55:29 EDT

>But I'm coming to the conclusion from my experiments and some concurring
>messages, that air core coils are quite superior.


Of that there is no doubt. Air cores are superior to anything with core with
regards to temp. stability and, generally Q because to be self-supporting,
they are wound with larger wire. Problem is, most projects now-a-days don't
have room in them. Consider the VFO coil you are working on. How big would
it have to be to work on 40 meters and how much space would you have to leave
around it to avoid unwanted coupling problems. We would probably be much
better off, in general, if we used larger cases and air solenoid inductors
because we wouldn't be as tempted to cram everything together into a Sucrets
box (oops, Altoids box).

Consider the W1AW problem with the QRP+. By simply re-routing a coaxial
cable, the problem is cleared up or greatly reduced. There's a lot of stuff
in that little package. Now, don't misunderstand. I love the Plus. I'm
glad that Index got it into that little package. It just highlights the
problems of unwanted and unexpected interaction when you get everything so
close together.

Begining builders take note. If you are building from scratch without the
benefit of a kitted design that SHOULD assure reproducibility, don't pick a
case that is too small. Give yourself some room to work and give your
electronics some breathing room (both thermally and electromagnetically).
 You'll probably end up with more hair in the long run.

Ed Manuel, N5EM

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