Jim Lux wrote in
:

....

Interesting..
So the loss is about 0.12 dB/meter at 10 MHz, compared to, say, RG-58
at 0.04 dB/meter. That's a huge difference, especially since the
center conductor on the RG-58 is probably smaller than the zip cord
(what was the wire size? I think you cited 1.22 mm diameter? AWG 16?
or AWG 18?)


The sizes came from Jack. 1.2mm is about #16.5.

The loss model suggests that dielectric loss is significant, even at
10MHz. Yes, I think you are correct that the inner conductor of RG58 is
fractionally smaller. IIRC, about 80% of copper loss in coax is in the
inner conductor, so the ZIP cord is at the disadvantage of having a
smaller 'other conductor' compared to the shield of the coax. There may
be some further degradation due to proximity effect. (Of course, ZO
favours the ZIP line.)

It seems that the copper loss is close to four times what might be
expected of round copper conductor. I don't know whether the conductors
were tinned, and what the effect of stranding was.

Another possible source of loss is radiation as I mentioned in the
earlier posting.

I note that Belden ceased supply of its 75 ohm twin lines, though I
think they used PE dielectric. Their #13 (8210) seems to have higher
conductor loss than accounted for by round copper conductors with normal
skin effect.

I can't help but be suspicous that proximity effect is a significant
part of the reconciliation gap.

Owen