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.
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