----- Original Message -----
From: "Tom W8JI" <w8ji@w8ji.com>
To: <topband@contesting.com>
Sent: Monday, December 31, 2012 7:56 AM
Subject: Re: Topband: single wire Dielectric covering.
Dielectrics affects/increases capacitance.
Question: Has anyone made a study as to how it lowers the frequency of
the wire that it is covering?.
My thought.... It is probably is a linear capacitance along the wire
itself.
While the dielectric and conductors inside the shield are not involved in
affecting electrical length or signal reception in the antenna mode,
multiple factors are at work outside the shield. The same is true for a
single wire.
How things affect the system depends on the electric field distribution in
the "stuff" surrounding the conductor.
It is impossible to insulate or isolate the electric field because it
passes through dielectrics. This is why buried open wire line, even when
suspended in a plastic pipe, has much higher loss and slow Vp than the
same line does with air surrounding the line for several wire spacings
away.
Excellent paper. Understandable and believe-able.
It appears that dielectrics are possibly increasing the capacitance to the
air itself.
An experiment I would like to see:
Two near identical antennas except, one bare wire, the other insulated.
Measure the frequency of each in dry weather, and then in high humidity (not
rain or Ice)
Compare the frequency change of each, if any.
In broadcasting we have sleet melters as the frequency does change with
ice/sleet causing an increase in VSWR .
Also I have observed the frequency of a 10 meter ham dipole go lower with
heavy frost on the wire. In this case the frost may have become the
dielectric.
73
Bruce-K1FZ
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Stew Perry Topband Distance Challenge coming on December 29th.
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