[TowerTalk] Copper clad telephone wire

[Donald Chester]

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