Re: NEC-LIST: Hi-Q inductors

Dave Cuthbert wrote:
>...I built a solenoid inductor wound on a PVC Pipe form. The measured
>results are close to the K6STI results except for the exceptionally low
>measured Q....

Dave, thank you for your valuable contribution to this very
interesting thread. I look forward to reading your results of
rewinding the coil with magnet wire instead of hookup wire (which I
suppose was PVC-insulated). IMO another good experiment would be to
eliminate the PVC pipe form.

My own accidental experiment with a solenoid inductor of
PVC-insulated wire, about a year ago, may be worth reporting. I
bought an amateur-radio "legal-limit" (1500 watts) HF antenna-tuner
which included a common-mode choke (a "1:1 current balun") comprising
a bifilar solenoid close-wound on a large (at least an inch in
diameter, and at least six inches long) ferrite rod. My first sight
of this choke alarmed me, because it was wound with what looked and
felt to me like PVC-insulated wire. The wire was copper, stranded,
AWG 12. It was the insulation that alarmed me, because previous
experience had taught me not to wind a coil with PVC-insulated wire.

So, before putting the tuner into service, I tested it simply by
putting 100 watts from my ham transceiver through it into a 50-ohm
resistive dummy load, at a frequency of 28 MHz, continuously for a
few minutes; then I shut off the power. The PVC-insulated winding of
the choke-balun was quite warm to the touch, and it _smelled_ "warm,"
too. It was obvious that putting 1500 watts through this device
would not be safe.

I replaced the PVC-insulated wire with Teflon-insulated wire and
repeated the experiment. Now the winding stayed cool even when I put
1500 watts through the tuner. (The ferrite core became slightly
warm, but not alarmingly.)

I'm sorry not to have a quantitative result to report; but, IMO, this
little experiment was quite damning for PVC insulation.

73 de Chuck W1HIS

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