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

[Jim Lux]

On 3/26/14 3:17 AM, Steve Hunt wrote:
> I made some further measurements this morning on a length of 10A
> Figure-8 power cable typical of the sort I've seen UK Hams press into
> service as RF feedline; the dominance of the dielectric losses was even
> more apparent!
>
> The cable comprised 28x0.19mm copper strands inside a 3mm diameter PVC
> jacket. Zo was measured as 130 Ohms and Vf as 0.66.
>
> These were the Copper losses, Dielectric losses and Total matched losses
> per 100ft derived from the measurements:
>
> 1.8MHz: 0.2dB, 0.15dB, 0.35dB
> 3.5MHz: 0.3dB, 0.3dB, 0.6dB
> 7.0MHz: 0.4dB, 0.6dB, 1.0dB
> 14MHz: 0.6dB, 1.1dB, 1.7dB
> 28MHz: 0.8dB, 2.2dB, 3.0dB
> 50MHz: 1dB, 4dB, 5dB
>
> As you can see, the dielectric losses exceeded the copper losses at any
> frequency above 3.5MHz!
>

This is interesting..
Vf of 0.66 implies that epsilon is about 2.3, which seems reasonable 
(partly plastic, partly air, but mostly plastic).

An interesting test would be to see if the copper losses go as the 
square root of frequency (skin effect) and dielectric losses go linearly 
with frequency.