[AMPS] RE: Power handling of Coax

[i4jmy@iol.it]

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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