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. 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.
If the RF voltage is in the MHz to VHF range, at 5 kV or more,
consider the power loss, esp with CW power.
* Amoco Performance Products registered trademark
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