The characteristics of #12 THHN and such vary all over the map. It is not
being made for use at RF. The insulation not only changes the velocity
factor, but it also adds loss. This too varies all over the map.
Wireman has various wires with UV resistant black PE insulation. That
stuff seems to be predictable and stable. I personally don't know of any
THHN with PE insulation. YMMV, of course. Neither of the guys at Home
Depot and Lowes have any idea what I'm talking about if I mention PE
insulation. Apparently plastic is plastic :>).
73, Guy
On Sun, Dec 30, 2012 at 4:55 PM, Charlie Cunningham <
charlie-cunningham@nc.rr.com> wrote:
> Well. it's not really the "quality" of the insulation -it's its relative
> permittivity - relative to the permittivity of free-space (or a vacuum)
> The
> "dielectric loading" of having a layer of higher permittivity material
> surrounding the wire causes waves propagating down the wire to travel a bit
> more slowly, thereby increasing its electrical length.
>
> Charlie, K4OTV
>
>
> -----Original Message-----
> From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Bruce
> Sent: Sunday, December 30, 2012 1:15 PM
> To: topband@contesting.com
> Subject: Topband: Fw: Short Bogs
>
>
> .>> If we want to make an antenna electrically longer through cable
> velocity
> >> factor, it can't be done by the insulation slowing the wave inside
> >> the shield.
> >>
> >> 73 Tom
> >>
> > In my experience, external insulation (through synthetic covering or
> > frost) lowers the resonant frequency of wire antennas of a given
> > length and height above ground.
> >
> > For example, I typically use 453/F as a starter length for insulated
> > wire dipoles...it's higher for bare wire of the same AWG diameter.
> >
> > It may not be due to "velocity factor" (not sure of the reason), but
> > it is observable and repeatable.
> >
> > 73, Gary NL7Y
>
>
> I also have had insulated wires of the same AWG diameter resonate lower in
> frequency than bare ones of the same length.
>
> Think we need multiple people experiment:
>
> Put up an antenna with covered wire. Measure the frequency, then cut the
> insulation away (of this same piece), and re-measure the frequency.
>
> If we get different results from different people, then we can start
> looking at the insulation. Is it economy grade made for 60 cycles (600
> volts), or is it the good stuff ???
> 1. If it is low grade insulation with resistance at 1.8, 3.5 MHZ, then it
> may be making the wire appear to be "fatter". If true, then that would be
> valid reason.
> 2. If the insulation is high quality at HF radio frequencies, and IF the
> frequency changes, then we need to look further
>
> 73
> Bruce-K1FZ
> www.qsl.net/k1fz/
>
> _______________________________________________
> Stew Perry Topband Distance Challenge coming on December 29th.
>
> _______________________________________________
> Stew Perry Topband Distance Challenge coming on December 29th.
>
_______________________________________________
Stew Perry Topband Distance Challenge coming on December 29th.
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