PTFE isolated coax are not used because of a lower loss.
Actually, PTFE coax losses are greater than similar size air, foam or
PE dielectric cables as the operating frequency is raised and the ohmic
losses become neglegible if compared to the dielectric losses.
The reason to use (short) teflon cables in labs and other special
applications lay in an inherent stability (mechanical, electrical and
to polluting or aging agents) or to be able to withstand quite high
temperatures without having a dielectric that melts and leads to lose
the conductors concentricity or even to let them to short.
A typical amateur radio application of PTFE cables (is) can be the
wound chokes and baluns on the antennas, or anywere a smaller size
cable (i.e. something like the RG142 instead of an RG 213) is a
convenient choice and the losses are anyway limited, as an absolute
number, because of a short cable lenght.
73,
Mauri I4JMY
> > The inner dielectric's ability to withstand the heat and its
effectivenuess
> > in transferring heat to the outer shield and jacket are the
limiting agents
> > in the heating process. For vhf/uhf use, coax with a teflon inner
> > dielectric are used, which permits a center conductor operating
temperate as
> > high as 250 C.
>
> I'll agree with this. The teflon also has low loss.
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