[AMPS] Properties of plastics at 10 GHz

[Richard W. Ehrhorn]

Delrin is an EXCELLENT dielectric throughout the hf range, but its melting 
temp is fairly low - somewhere in the vicinity of 100 C I'd guess. So of 
course it will melt if nearby current-carrying conductors transfer enough 
heat to it -- as, perhaps, in some typical roller coil designs.

In my experience Nylon is lossier than Delrin, at least @ hf. According to 
the characteristic tables it absorbs much more water - don't know if that's 
a major factor in the higher rf loss, but believe it can lead to decreased 
dielectric breakdown strength.

OTOH, Nylon is available in flame retardant grades (UL types), which so far 
as I know Delrin isn't. It burns fairly readily and emits a thick, oily 
smoke that tends to leave a black, greasy film on nearby surfaces.

73, Dick

-----Original Message-----
From:	Rich Measures [SMTP:measures@vc.net]
Sent:	Thursday, August 13, 1998 9:12 AM
Cc:	amps@contesting.com
Subject:	Re: [AMPS] Properties of plastics at 10 GHz


>
>By coincidence I was working on a project involving use of plastics
>at near 10 GHz when the original post was made.  Ill say again,
>Rich (and you) got it wrong.  Nylon, vinyl, or delrin are poor
>absorbers at 10 GHz.
>After reading Jon's post and agreeing with him I realized I had
>everything I needed to verify it on my work bench.
>I measured insertion loss of a piece of waveguide then plugged it
>with delrin 1/2 Wave thick at the test freq and again checked
>insertion loss of the waveguide.  After calculating out the mismatch
>losses caused by the delrin plug I had the same insertion loss as
>before.  A plug several wavelengths long gave the same results.
>73, Bob, W5AH
>
So Delrin has virtually no loss at 10GHz, however, it melts readily in
roller coils at HF?


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures


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