>
>At 11:45 PM -0500 11/12/01, owner-amps-digest@contesting.com (RF
>Amplifier Discussion Dige wrote:
>> >PVC isn't the best material for the job: if you can get some fibreglass,
>>>that's much better - less loss.
>>
>>ABS has a lower Dissipation factor than PVC . G10 and G11
>>epoxy-fiberglass have a low D factor.
>
>
>And G7 is even lower loss than G10 material. The glue/binder is
>silicone based. But its harder to work with and nearly impossible to
>turn i a rod on lathe to cut 'wire' grooves. For this we have gone to
>using Udel* polysulfone rod. ASTM D150 (1 MHz) measured dielectric
>properties: K = 3.14 and dissipation factor is 0.0008.
? Excellent. However, for HF at 7kV of RF, G10 worked well in the
"Plywood Box" 8170 20db amplifier. Fabrication with G10 is a piece o'
cake.
> 425 v/mil
>dielectric strength. Its available from the same plastic distributors
>as the fiberglass stuff if you ask.
>
>I used to recommend crosslinked polystyrene (Rexolite, Q200.5) for
>coil forms in high powered RF systems, however, it is so hard and a
>bear to machine, also it tends to melt and surface track if there is
>an arc. Teflon** is most resistant for this, but we all know what a
>pain it is mechanically. For chokes though, it is great stuff, as
>long as you are careful not to overheat it during fabrication and/or
>breathe the dust.
>
>Of all the polymers, I wouldn't recommend nylon, Delrin**, PVC and
>even ABS pipe as these are not 'electrical grade' polymers. Of
>course, if you have experience using ABS and it doesn't heat up or
>lower Q, then have at it.
ABS is one of the styrenes. The D-factor of styrenes is generally low.
>If the RF voltage is in the MHz to VHF range, at 5 kV or more,
>consider the power loss, esp with CW power.
>
Fire is a fairly reliable indicator of too much loss.
cheers, John
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
end
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