[TowerTalk] 75 or 70 Ohm twinlead or ladderline cable - does it exist?
steve at karinya.net
Wed Mar 26 06:17:12 EDT 2014
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
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!
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