One of the problems with using ordinary twin flex as an HF transmission
line is the relatively high dielectric losses associated with the
typical insulation materials used; so our usual assumption that
dielectric losses can be ignored at HF may be untrue.
If we take RG213 as reference, the dielectric losses at 3.5MHz are 3% of
the total, at 10MHz they are 6% of the total, and the dielectric losses
don't exceed the copper losses until we get above 2500MHz.
However, measurements on a PVC insulated twin pair showed that the
dielectric losses at 3.5MHz were 27% of the total, at 10MHz they were
40% of the total, and the dielectric losses exceeded the copper losses
at any frequency above 23MHz.
Steve G3TXQ
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