> From: Larry McDavid <lmcdavid@lmceng.com>
> Reply-to: lmcdavid@lmceng.com
> To: amps@contesting.com
> Subject: [AMPS] Delrin Spreaders
> Organization: LMC Engineering
To: <amps@contesting.com>
> Date: Fri, 20 Jun 97 12:37:56 +0000
Hi Larry,
> What would you recommend for spreaders, not on ladder line but for
> parallel dipole spreaders? Delrin is readily available in both natural
> and black. The black has good UV resistance.
The whole "dissipation factor thing" seems to be an out-of-
context explanation. We should really look to see how the change
affects the system. (A similar thing occurs when people worry about
nylon insulators in PA systems causing undue loss.)
Dielectric loss relates to the electric field intensity in the
material, as well as the dissipation factor. We explain how "current
flows through insulators" in the term of displacement current.
It seems to me there is simply not enough displacement current in
the Delrin to worry about, if the insulators are spaced along the
line a reasonable distance.
While it is true the poorer dissipation factor would produce a
few hundred times the amount of heat produced in ceramic dielectric
under the same conditions, many times an insignificant quantity often
remains insignificant
Even in coax, with solid polyethylene insulation, RESISTIVE losses
dominate the system. The main reason air-foam insulation reduces coax
loss is the CONDUCTOR size gets bigger, it is NOT because of the
dissipation factor change.
Perhaps Rich will show us his calculations that demonstrate the
temperature rise and power loss would be significant, or explain
what led him to his gut feeling?
73, Tom W8JI
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