Re: VFO Stability

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From: John F. Woods (jfw@jfwhome.funhouse.com)
Date: Tue Aug 08 1995 - 07:56:16 EDT


> Meanwhile, the basic consensus is that ANY core material is a
> compromise for VFO use. An air core coil is by far the most stable
> inductor to use. The traditional ceramic form is most recommended, with
> glass tubing and acrylic rod also getting some nods.

True, but it turns out that air core is also something of a compromise:
the disadvantages are the large physical size (obviously), and the coupling
to other circuits. (Enclosing an air core inductor in a metal can lowers
its Q because of the coupling to the can.) Toroids are self-shielding and
have little (if not quite no) coupling to nearby wires.

I believe the -7 material has a TC of +30ppm/*C, as opposed to -6 which is
+35ppm/*C (a small difference, but better than nothing). I happen to have
a bunch of T44-7 cores, from when Amidon accidently shipped me T44-7 instead
of T50-7, and then sent, as replacements, another batch of T44-7...


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