Steve,
Sure makes one think about where and how the loss of Q is occurring.
Unused turns can couple to the active portion of the coil, reducing Q.
Another factor that comes to mind is the shorting rod that impresses a wheel
against a coil or in the case of an edgewound variable, the shorting bar to
the wiper contacts. Coils wound on solid dielectric material is also a
factor unless the coil is air-wound.
In my homebrew motorized tuner, a pair of Collins silver tape inductors are
used on ceramic forms which supposedly keeps Q reasonably consistent as a
function of F and L. Unused tape spools up on a conductive cylinder. There
are no moving contacts. I've not tested one of these coils but it would be
worth the effort to see if the claim is true or not.
Link-coupled tuners with plug-in coils designed for single-band operation
generally do not suffer from Q loss. Link coils made from B&W Airdux or
free standing coils made from stiff copper tubing are capable of keeping Q
very high.
Paul, W9AC
----- Original Message -----
From: "Steve Hunt" <steve@karinya.net>
To: <TowerTalk@contesting.com>
Sent: Monday, November 29, 2010 2:11 PM
Subject: Re: [TowerTalk] Tuners
> Paul,
>
> I made the measurements myself. The inductor was in the open, sitting on
> a wooden baseboard. It had a "tapered pitch".
>
> The Qs I measured seem to be similar to those measured by Tom W8JI who
> says this on his web site:
>
> "The trend of Steve's data agrees with my measurements, although there
> are differences in data because I measured different inductors. I
> measured less peak Q, but also significantly higher minimum Q in the
> inductors I tested. While the inductors I measured has less delta in Q,
> they also had a serious dip in Q up near 25-35 MHz when near
> half-inductance."
>
> 73,
> Steve G3TXQ
>
>
> On 29/11/2010 17:50, Paul Christensen wrote:
>> Steve,
>>
>> Do you know if the plots were obtained with the roller inductor placed
>> away
>> from surrounding objects -- or placed within a metal cabinet? The Q
>> looks
>> pretty pathetic above 40m.
>>
>> Also, anyone know if Q improves toward 10m when using a roller inductor
>> with
>> a non-linear turns count that allows for more turns per unit of
>> inductance
>> at one end? (e.g., Cardwell 229 series)
>>
>> http://www.cardwellcondenser.com/PAGES/md04g.html
>>
>> Paul, W9AC
>>
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