[TowerTalk] 75 or 70 Ohm twinlead or ladderline cable - does it exist?

[Steve Hunt]

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