-----Original Message-----
From: Charlie Cunningham [mailto:charlie-cunningham@nc.rr.com]
Sent: Monday, December 16, 2013 4:32 PM
To: 'Tom W8JI'; 'Topband Reflector'
Subject: RE: Topband: Insulator problems- Notr og caution
All good points.
We have used gray UV-stabilized poly carbonate to mold covers for
electricity watt-hour meters that had some rather stringent requirements fr
with standing ambient sunlight.
The problems that I encountered with black plastic that was blackened with
carbon-black, the cheapest and most readily available material for
blackening plastic, was in portable and water-meter pit devices whose
transceivers operated io the 902-928 MHz ISM band, The black plastic,
containing carbon-black would totally destroy the tuning and radiation
efficiency of embedded antennas. There are other dyes and materials that can
be used to blacken plastic, but one has to take care to specify the
materials and or the electromagnetic properties of the plastic that is used!
It's not so much an insulating problem, rather it has to do with the
absorptive properties o ftne material at VHF and UHF. Not so sure about HF.
But I've made lots of end and center insulators for antennas from
polycarbonate sheet stock!
73,
Charlie, K4OTV
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Tom W8JI
Sent: Monday, December 16, 2013 4:09 PM
To: 'Topband Reflector'
Subject: Re: Topband: Insulator problems- Notr og caution
I don't want to belabor this, because I think Greg was going to try Delrin,
but Delrin homopolymer is slightly different than other acetal resin
copolymers. They are similar, but not exactly the same.
1.) Black does not always mean poor insulating ability. It will be fine at
HF
2.) Black also does not necessarily mean better UV resistance. It generally
helps, but many white materials are good. I have white tower ropes that
outlast black rope. It really depends a great deal on the UV inhibitors and
the material. Most white nylon ropes contain UV inhibitors, for example.
If he wants to get a special grade of Delrin, 527 UV would be most UV
resistant. The little bit of carbon pigment won't hurt a thing at HF.
Greg is in New Zealand, so he will probably have to buy what is available.
Since nylon lasted a few years, the material doesn't have a high bar to
jump.
73 Tom
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