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.
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Stew Perry Topband Distance Challenge coming on December 29th.
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