"Chris Suslowicz" wrote in
message ...
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?

The signalling is "point to point", and there would have
to be relays
to cut the effective line capacitance into manageable
chunks in order
to get a reasonable transmission speed.

The military method was "outstations" to "signal office",
then "office
to office" and finally to the recipient. Paper copies of
the traffic
would exist at each office, and be destroyed once the
message had "cleared"
(I.e: been transmitted to the next office in the chain and
been
acknowledged as having been received correctly.)

They also used multiple sets on a single pair for long
runs, and yes:
all the intermediate stations could hear the traffic -
otherwise they
wouldn't know when there was a gap in the traffic into
which they could
insert the offer of a message to another station.

A lot of civil traffic would be in code anyway - not to
make it unreadable
by the telegraph staff, but simply to cut transmission
costs by having 5
character groups to represent standard
words/phrases/paragraphs of contracts,
etc.

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.

I've got some books on (the military side (British))
telegraph line
construction and operating procedure, but not the civil
side.

Chris.

I don't think capacitance was so much the problem as
just plain resistance. Telegraph systems used repeaters at
periodic locations. There were several variations of
repeaters, some simplex and some duplex, but all were
arrangements of sensitive relays. There were also two
variations of sounders, local and line, varying mainly in
coil resistance. Typical local sounders were about 4 ohms,
line sounders could be anything from about 20 ohms to maybe
150 ohms. I have a maintenance sounder from Western Union
which is 400 ohms.
Line loading came fairly late when high speed and
multiplex telegraph systems began to be common. As with
telephone service periodic loading increased bandwidth (and
hence speed) at the expense of greater overall loss.
There are several sites on the web dedicated to old
telegraph equipment and a number of technical handbooks
available in PDF form from Google Books (free downloads but
some are not scanned very well).


--
---
Richard Knoppow
Los Angeles, CA, USA