At 06:25 AM 7/28/2007, Jim Jarvis wrote:
>In high-precision measurement systems, distinction was made between teflon
>and PTFE, as to differences in dielectric properties. If you're measuring
>charge..and using teflon cables...it could take several minutes to discharge
>the teflon cable capacitance to allow a proper measurement....whereas PTFE
>has a lower dielectric constant, due to the micropores. i.e. Same stuff,
>slightly different form.
It's probably not all that relevant at HF (the phenomena may not
exist), but some PTFE insulated cables have a non-uniformly varying
phase vs temperature characteristic, with a step around 15-20C.
http://www.gore.com/en_xx/products/cables/microwave/changes_insertion_loss_phase.html
This would be about a quarter of a degree in a 100 ft run at 30 MHz,
probably not enough to worry about in a phased array. The
attenuation also has a bit of a step, too.
The Gore stuff is interesting, because the dielectric is actually a
long flat strip that is spiraled around the center conductor.
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