> From: Rich Measures <measures@vc.net>
> To: <AMPS@contesting.com>
> Subject: Re: [AMPS] Delrin Spreaders, a test
To: <amps@contesting.com>
> Date: Mon, 23 Jun 97 13:24:49 +0000
> >AG6K wrote:
> >
> >> My first experience with the significance of dissipation-factor was when
> >> I used a General Radio Co. NYLON double-banana plug at the end of a home
> >> made open wire feedline. The nylon melted and began foaming. I changed
> >> the plug to one made from phenolic.
>
> The amplifier being used at the time was an SB-220.
I see. My test today was with 50 watts.
50 watts can generate many kV, so the problem is one of voltage and
not power. That is my point.
> >> My second experience was with PVC pipe near the end of a 40m dipole. As
> >> I was tuning up a home brew AB1/tetrode amplifier, the telephone rang.
> >> My neighbor said: "Rich: your antenna is on fire." My gut feeling was
> >> that the presence of flames and smoke indicated that it was quite
> >> possibly on fire.
> >> - [note: the amplifier was delivering about 1150v peak to the RG9
> >> feedline at the time]
> >> -Rich-
> >That's about 8 kW if the line is matched, but of course none of that
> >gives us any idea what voltage the delrin or nylon failed at.
> >
> 1150v peak into 50 ohms is not 8kW according to ohm's-law, Mr. Rauch.
You're correct. I thought RG-9 was 75 ohm cable, but I see it is 50
ohms. I should have looked in the Belden catalog instead of guessing.
That's about 13 kW into a 50 ohm load.
>From what I saw today..... I wouldn't worry about Delrin or Nylon
unless the insulator occupied the bulk of the e-field area around the
conductor, or the voltage approached the corona point of a small
diameter wire.
73, Tom W8JI
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