In article ,
COLIN LAMB wrote:
I never thought about this until the matter came up in the HQ-145 thread,
but what was the process of sending messages over the telegraph lines?

Suppose I was in a small town in Oregon and wanted to send a message to a
small town in Nebraska? Is the message "broadcast", or does it go to a
clearinghouse? Can anyone on the "wire" listen in? Are there relays?

I have been a ham for almost 50 years and I have no clue. There must be
some OT who are just waiting to tell me, or know a good website.

Authoritative answer: "It depends." grin

A single telegraph line could have multiple stations on it, with 'common'
wiring -- anything from one station on the line was echoed at _all_
the other stations -- more-or-less broadcast.

A given 'line' spanned a relatively limited distance, so 'long-haul' messages
went through relay/distribution centers between origin and final destination.
These were 'store-and-forward' facilities, rather than 'repeaters'. i.e.,
the operator on one line received the message, copying to paper, and passed
to the operator on the other line for re-transmission. Late versions of
the system replaced the 'relay' operators with electromechanical devices.
(And *NOW* you know where the name for those solenoid switches comes from

By the time the telegraph network was widespread, the "long distance" lines
were (_almost_ exclusively) only 2 stations -- enough traffic flowing end-to-
end (and beyond) that there was no net benefit to additional drops on the
line.

The 'edges' of the network -- mostly small-time rural America -- were another
story. 40 miles was a full days ride on horseback. If you were 10 miles out
of town, getting to/from town was a _half-day_. Outposts of civilization,
thus tended to be as close as 15-25 miles --- in the mountains, even closer.
Several stations, "party-lined", on a single 'line' were common. I'm not
aware of any commercial line where the station count was out of the single
digits, but I'm no expert on the matter. grin Mine telegraphs could have
*lots* of stations on the same 'paralleled' line, as various levels were
worked out, and additional horizontal bores were run.


Where you had several stations on a single line, there was a code for each
station on that line -- a multiple-duties operator could ignore an 'alert'
that was -not- prefixed with his code. If it was addressed to him, he'd
key a 'go ahead' when he was ready to receive.

The most common wiring set-up was straight series -- in each station, the
key and sounder were in series, and the stations were in series with each
other. This only needed one overhead wire, with an 'earth' ground return.
One disadvantage was that each key required a shorting switch when not in
use. Failure to short the key resulted in an 'open' circuit, with no
messaging possible until the key was closed. Same problem if any of the
sounders failed 'open'.

This was, obviously, a voltage-driven configuration -- more stations 'on line'
required higher driving voltage to ensure that the voltage drop across each
sounder was sufficient for operation.

There was another set-up used, primarily for shorter distances, and where
stations were only intermittently installed/manned -- seasonal stations,
or 'in-mine' wiring, for example. This was multiple wires 'in parallel',
with a simple T-tap wherever a station was needed. First wire was the
'battery' supply, and was tapped to feed one side of the key. Other side
of the key went back to the second wire. The sounder was wired between
the 2nd wire and 'ground' (sometimes a 3rd wire, sometimes 'earth').

Had the advantage of -not- requiring a shorting switch on the key, better
for the 'occasional' operator. AND a failed sounder did not disable the
other stations.

Had the disadvantage of requiring 2-3 times the wire of the series setup.

This configuration is current-driven -- a constant voltage requirement -- but
the current running through each key (when closed) has to drive all the
sounders.