This is an interesting thread. Lots of new high tech materials to
choose from for making antenna insulators. While we are considering the
various attributes of these promising solutions lets not lose sight of
the fact that you can still buy high voltage quality ceramic insulators
specifically designed for antenna applications for prices in line with
the costs of the cutting boards being considered.
John Lyles wrote:
>Exactly, 2450 MHz microwave fields are probably not as important as
>mechanical strength, HV breakdown, water absorption and mechanical
>properties for antenna insulators.
>
>Microwave ovens generate a relative low field strength, compared to
>those at the ends of dipole antennas and resonant circuits with kW
>levels at HF. I use a commercial dielectric heater at 90 MHz, that I
>bought at a junkyard, to test plastics and hoses for RF amplifier work.
>It subjects the material, typically about an inch thick or less, to
>fields such as 15 kV peak. If a material is to be trusted in a high
>field environment, such as supporting components in a tank circuit or
>hoses to the plate of a water cooled tube, this test is much more valid
>than a microwave oven. Materials that just are barely warm in the
>Radarrange sometimes erupt in smoke and melt in the dielectric
>preheater. The white cutting board UHMW PE is pretty good, not as good
>as Teflon but acceptable.
>
>But for center insulators where the rf voltage is readily calculated
>from P=E^2/Z, the electric field won't eat UHMW PE or the like. In this
>case, you want to prevent tracking when the material is wet, or
>contaminated with dust, smoke residue, or after aging in the sun.
>
>73
>John
>K5PRO
>
>
> >Message: 6
> >Date: Sun, 22 Apr 2012 07:54:01 -0700
> >From: Jim Lux <jimlux@earthlink.net>
> >Subject: Re: [TowerTalk] Plastic Cutting Boards for Antenna Stuff ?
> >
>On 4/22/12 7:14 AM, Bill Harris wrote:
> >> Zapping a piece of material in the microwave for a minute or so,
> >>should give you some idea what the insulating properties are. If it
> >>doesn't get hot, (how hot?) it should be okay for an insulator at HF
> >>frequencies, right?
>
> >the microwave test is sort of so, so.. it's at 2.5 GHz and it more
> >measures RF absorption than things that are actually more important
> >like HV breakdown and water absorption.
>
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