The copper clad stuff was probably used for railway telegraph lines. Ordinary
open-wire telephone lines used galvanised steel, and in most cases by the time
the lines were taken down, the zinc coating was long gone, and the wires were
largely rust. They used copper clad next to the train tracks because smoke from
the high-sulphur coal used to power steam locomotives was very corrosive, but
copper was far more resistant to that environment than was steel, even
galvanised.
I picked up several thousand feet of #10 copper clad back in about 1970 when
the old telegraph lines were taken down. A workman told me where it was, and to
come take all I wanted. They would cut the wires at every few poles, about
every 750 ft. and remove the cross-arms, insulators, wire and all from the
poles in between and leave it beside the tracks for the salvage crew. The
railway guy said that it was hardly worth salvaging, because at that time
copper clad steel was all but worthless as scrap metal. I loaded all I could
carry in my vehicle. Although it was covered with a green patina, nearly all
the copper was still there after many decades of exposure.
I used it for antennas, open-wire feeders and ground radials. The soil here is
approximately neutral PH, and copper seems to last a long time when buried in
the soil. I still occasionally run into buried remnants of those radials and
they have always still had plenty of copper left on the wire.
The way I measured the depth of copper on mine was to take a small piece, clamp
it into a bench vice and carefully file a flat spot using a fine grade hand
file until I could just barely notice a thin line of bare steel with a
magnifying glass as I filed through the copper. Then do the same for the
opposite side, making sure to keep the position of the file parallel with that
of the first side. At the first sign of steel core on both sides, measure the
outside diameter of the un-filed wire with a micrometer or vernier callipers,
and then take another reading at the spot where the wire was filed. Subtract
the two figures, divide by 2, and that should give the thickness of the copper
skin. To be more exact, if you have the time and patience, repeat the procedure
2 or 3 times at different spots along the wire.
I don't think it's very critical at all. I ran a 140' length of open wire
feeders using #8 copper clad from a big roll that was given to me free of
charge, probably military surplus. The copper jacket was probably thinner than
that of the #10, measuring just a little over one skin depth at 1.8 mHz. I was
afraid it might have excessive loss at 160m, but I measured the efficiency
using a dummy load the same impedance as Zo of the feeders at the far end. I
ran 100 watts DC input to the final and took rf current readings at various
frequencies using a thermocouple RF ammeter in series with one leg of the OWL,
first at the transmitter end, and again at the far end next to the dummy load
and compared the sets of readings. My calculations indicated 98% efficiency.
I ran a similar test with a 140' run of fresh RG-213 using an RF ammeter and a
50-ohm dummy load, and the efficiency calculated out to be between 92 and 93
per cent. I verified the tests using a Mirage wattmeter, and the results were
very close to the same. So I decided that the copper clad was perfectly OK for
my purposes, particularly since I have a large roll of it on hand.
The fellow who gave me the #8 used it to guy three towers, each about 100'
high. He said they had been up for about a decade and had survived several
severe wind storms. I don't know if I would use it for permanent guys, but I do
plan to use some for temporary guys when I replace some of the rusted 3/16 EHS
guy wire on my 127' tower, which I hope to get done before winter sets in. One
problem I could see with using copper clad anything for guy wires would be
electrolysis between the copper wire and galvanised steel tower. I would
recommend using johnny ball insulators at each end of each guy even if you
weren't planning to break the guys up with insulators. Be sure to tightly wrap
each termination with plenty of turns. I used some of the #8 copper clad for my
Beverage receiving antenna, and clamped the terminations with copper or brass
split bolts like electricians use for splicing electric power conductors.
Ordinary cable clamps are zinc coated, and in contact with the copper, would
rot away in no time.
Don k4kyv
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