Re: NEC-LIST: Coil-loading.

Jack,

I will have to get to the bottom of this and figure out how to
accurately predict solenoid inductor Q. I will report back when I figure
this out. Can you steer me to some papers on this subject?

I built an air core coil with #16 AWG and measured it at 1/5 of the SRF.
The Q is 38. It is 18" from any objects and is series resonated with a
150 pF ceramic capacitor to get the measurement into the sweet spot of
the instrument. I tried a different type of ceramic and got the same
results. Q = 38.

The K6STI calculator returns a Q of 450 and hand skin effect
calculations (no shunt C and no proximity effect) give a Q of 1000 at 4
MHz.

   Dave Cuthbert

-----Original Message-----
From: Jacob Schanker [mailto:schanker_at_frontiernet.net]
Sent: Monday, February 07, 2005 9:57 AM
To: drcuthbert; nec-list_at_robomod.net
Subject: Re: NEC-LIST: Coil-loading.

Dave:

I would believe 1000 only if I saw it.

I've done a lot of high Q inductors over the years, from silver plated
oxygen-free copper tubing for 4 kW antenna multicouplers to litz wire on
fiberglass 6 inch diameter coils for LF antenna tuners, but to the best
of
my recollection, 450 or so was about the Q limit I achieved. I've also
done
helical resonators for preselectors, and don't think I reached even
close to
1000. That doesn't mean that some better engineer couldn't outdo me, but
pretend I'm from Missouri (Rolla, if you like) and show me. :)

Regards,

Jack

Jacob Z. Schanker, P.E.
65 Crandon Way
Rochester, NY 14618

Tel: 585 442 3909
Fax: 585 442 2182
j.schanker_at_ieee.org

----- Original Message -----
From: <drcuthbert_at_micron.com>
To: <nec-list_at_robomod.net>
Sent: Monday, February 07, 2005 11:13 AM
Subject: Re: NEC-LIST: Coil-loading.

> Doug,
>
> A Q of 300 can be achieved with close spacing of the windings on a
> dielectric rod. A Q of nearly 1000 can be achieved with a properly
> designed air-core solenoid inductor.
>
> Dave Cuthbert
> Micron Technology
>
> -----Original Message-----
> From: nec-list-bounces+drcuthbert=micron.com_at_robomod.net
> [mailto:nec-list-bounces+drcuthbert=micron.com_at_robomod.net] On Behalf
Of
> D. B. Miron
> Sent: Monday, February 07, 2005 8:35 AM
> To: nec-list_at_robomod.net
> Subject: Re: NEC-LIST: Coil-loading.
>
> Good day,
>
> Jim is right about the original question. I have a 1943
> copy of Terman and I don't see anything about coil loading.
> He has a very brief paragraph on automobile antennas in
> which he mentions the whip, and plate antennas.
>
> A related question is about coil Q. I read somewhere that
> the maximum practical Q or an air-core solenoid is about
> 300. Does anyone disagree, or have different experience?
> Thanks.
>
> Doug Miron
>
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