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Owen Duffy · October 25th 10, 05:54 AM posted to rec.radio.amateur.antenna

Tom Horne wrote in news:bc6994d1-be9a-45e6-8b56-
:

I have read that the presently available 300 ohm ladder line is
unsuitable to use at some amateur radio frequencies because of it's
construction and the losses caused by skin effect in the copper coated
steel construction. I have been using a Terminated Folded Dipole in a
flat top configuration as my HF antenna at home. Having recently
acquired an Icom AH-4 Antenna Coupler I am considering converting it
to a simple folded dipole, feeding it with 300 ohm ladder line to
match it's nominal impedance from the coupler. I know your sure that
there is a question in here someplace so is there better quality 300
ohm window line available that is entirely stranded copper in it's
construction?
--
Tom Horne, W3TDH

Tom, if you made a line of the dimensions of Wireman's 300 ohm line out
of HT steel, you would be looking at matched line loss at 80m in the
range 30 to 40dB / 100m, depending on the permeability of the steel wire.

If you made it out of copper, you would be looking at around 0.5dB.

The thing is that copper clad steel is somewhere in that range. If the
cladding is more than say, three skin depths in thickness, loss will be
almost identical to copper.Skin depth in copper is 35 microns, three
times that is 100 microns amongst friends.

The strands of 19 strand #18 are 200 microns in diameter.

I have no idea what the copper thickness is, but I suspect it is less
than 100 microns (as they would be pure copper in that case).

As Richard suggests, be perverse, ask the Wireman if he has measured loss
data for the line at 3.5MHz, not extrapolated data from higher frequency
measurements, but measured data.

I am not picking on the Wireman, Richard mentioned them, but I think the
same issue exists for all suppliers.

The only nominally 300 ohm line that is pure copper that I have seen is
TV ribbon, but that is probably not as good as you seek.

Think about the Wireman's 551 which is a single core CCS. If it is 30%
CCS, the cladding depth is about 7% IIRC, and that would make it 70
microns... might just scrape in with near copper performance on 80m.

The Rule of Thumb usually used is 2.5 to 3 times the skin depth gives
near copper performance.

Owen

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