I asked E. L. Trump a question about Morse lines and iron wire impedance problems over long distances. Ed's response deserves a wider audience, and he suggested that others might like to see it too. I certainly agree -- thanks Ed.
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Actually in the relatively arid climate in the Rocky Mountain west, telegraphy over open wire lines and with iron wire worked remarkably well as long as the lines were maintained properly.
As an example, Silverton on No. 108 wire took terminal battery and was relayed via Western Union Pueblo. Total length of that wire was only around 330 miles...about 40 miles Pueblo to Walsenburg, 75 miles to Alamosa, 34 miles to Antonito, 65 miles to Chama, 70 miles or so to Durango, and 45 miles to Silverton equals
about 329 miles, give or take a few miles...plenty within reason for a good wire kept properly maintained and instruments properly ajusted.
If"escape" or leakage to ground via poor insulation was kept under control by keeping brush and trees cut away from the wire, and keeping broken insulators replaced, an iron wire could easily be worked for hundreds of miles without any undue problems. Good copper wires would go farther than that by a considerable amount.
Wet weather, snow, etc. would require some "readjustment" of the instrument magnet armature spacings on the relays from time to time to reduce the influence of line leakage losses to earth and to maximize performance, but rarely did this completely prevent working a wire satisfactorily. Even if it did, an intermediate office could manually relay on the same wire if necessary, when it couldn't be worked all the way end-to-end.
Even though iron wire has resistance that is around three times what copper does (about 11 ohms per mile for No.8 galv. iron, versus about 3 ohms per mile for No. 8 HD copper), sufficient battery (The Western Union "standard" mainline battery voltage was 160 volts D.C.) applied at the terminal ends would keep things working pretty well.
We can figure it out today...330 miles of No.8 galv iron wire had about 330 x 11 = 3630 ohms resistance. A ground return circuit that long has NO (zero) resistance in the ground path. With 160 volts battery at each end, and say a dozen 150 ohm mainline instruments cut in at stations along the wire for a total of another 1800 ohms, the total resistance of the circuit would be around 5500 ohms, give or take a bit. With 320 volts of battery in the circuit (160 volts at each end), Ohm's Law I=E/R gives a line current of about 0.058 Ampere or 58 Milliamperes, which is just right for a telegraph wire.
Repeaters were typically only used where a Morse wire had to "branch" a considerable distance in two directions. Example, No. 5 wire from Cuchara Jct west to Alamosa, and south to Trinidad.
It was far more common to "loop" a Morse circuit up shorter branch lines rather than have to maintain repeaters and their associated battery and circuitry at smaller stations. The Pagosa Springs branch was one example...Telluride from Vance Jct on the RGS was another. AT&SF had a Morse loop to Magdalena N.M from Socorro.
Even with some minor faults or some leakage along the lines, the Morse system was still able to operate effectively, which is one reason it lasted as long as it did into the ages of more modern technology...A Morse wire could be worked satisfactorily for hundreds of miles farther than an unrepeatered telephone pair. Talking over such a long telephone circuit was made very difficult due to losses to the feeble voice currents, whereas a good Morse wire carried just fine, with signals loud and clear from the local circuit on the main line relay.
In the 1960's and '70's, I personally worked with iMorse wires on the D&RGW that ran from
Pueblo to Salida, Salida all the way to Grand Jct, Grand Jct to Helper, Utah, Denver to Craig, Colorado, etc. without repeaters...they worked very well over those distances.
The first transcontinental Morse telegraph wire put up in 1861 between Omaha and Sacramento eventually only had automatic repeaters at Fort Laramie in eastern Wyoming, Salt Lake City Utah, and Virginia City, Nevada which replaced manual relaying at those stations.
Of course, in the days when Morse wires were all there was to use, more and proper attention was paid to keeping the lines in good shape, a far cry from what began to happen when the open wire lines began to fall into disuse.
