RadioBanter - early telegraphs and relays

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Griff

May 3rd 04 10:39 AM

early telegraphs and relays

hi there everyone

I'm currently reading a book called "Code" by Charles Petzold which is
essentially a history and overview of computer technology, quite
entertainingly told. I've just read the section on telegraphs and
relays and am confused by something he has written.

He explains the basic principle of the telegraph, and goes on to show
with some simple Ohm's Law calculations that you can't extend the
length of telegraph wires indefinitely due to the loop resistance
etc., hence the need for the invention of the relay.

However, I am a bit puzzled by his summing-up quote for this chapter:
"Regardless of the thickness of the wires and the high levels of
voltage, telegraph wires simply couldn't be continued indefinitely".
Now I would have thought the restriction was *exactly* due to the
limitations on wire thickness and voltage (ie the practical problems
with manufacturing telegraph cables and voltaic cells at that time).
Or am I doing Mr.Petzold an injustice, when perhaps there was some
other limiting factor ?
I have read somewhere that there were problems with insulation for
very long cables, is this perhaps something to do with it ?

Any thoughts you may have are welcomed,

best rgds

griffph

KØHB	May 3rd 04 03:12 PM

"Griff" wrote

However, I am a bit puzzled by his summing-up quote for this chapter:
"Regardless of the thickness of the wires and the high levels of
voltage, telegraph wires simply couldn't be continued indefinitely".
Now I would have thought the restriction was *exactly* due to the
limitations on wire thickness and voltage (ie the practical problems
with manufacturing telegraph cables and voltaic cells at that time).
Or am I doing Mr.Petzold an injustice, when perhaps there was some
other limiting factor ?

Probably due to the cumulative C and L of a long wire eventually shaping
the waveform so that rise and fall profiles are smeared.

73, de Hans, K0HB

Alun	May 3rd 04 04:20 PM

"KØHB" wrote in news:Tqslc.3830$Hs1.3291
@newsread2.news.pas.earthlink.net:

"Griff" wrote

However, I am a bit puzzled by his summing-up quote for this chapter:
"Regardless of the thickness of the wires and the high levels of
voltage, telegraph wires simply couldn't be continued indefinitely".
Now I would have thought the restriction was *exactly* due to the
limitations on wire thickness and voltage (ie the practical problems
with manufacturing telegraph cables and voltaic cells at that time).
Or am I doing Mr.Petzold an injustice, when perhaps there was some
other limiting factor ?

Probably due to the cumulative C and L of a long wire eventually shaping
the waveform so that rise and fall profiles are smeared.

73, de Hans, K0HB

I beleive they used to add inductors to telegraph wires at intervals before
they had repeaters. This seems counter-intuitive to me, as I would have
thought the L was more of a problem than the C. Does anyone know the
correct explanation?

Alun, N3KIP

KØHB	May 3rd 04 04:23 PM

"Alun" wrote

I beleive they used to add inductors to telegraph wires at intervals
before
they had repeaters. This seems counter-intuitive to me, as I would
have
thought the L was more of a problem than the C. Does anyone know the
correct explanation?

Makes perfect sense to me. A parallel L would cancel the distributed C.

73, de Hans, K0HB

N2EY	May 3rd 04 05:17 PM

(Griff) wrote in message . com...
hi there everyone

I'm currently reading a book called "Code" by Charles Petzold which is
essentially a history and overview of computer technology, quite
entertainingly told. I've just read the section on telegraphs and
relays and am confused by something he has written.

He explains the basic principle of the telegraph, and goes on to show
with some simple Ohm's Law calculations that you can't extend the
length of telegraph wires indefinitely due to the loop resistance
etc., hence the need for the invention of the relay.

However, I am a bit puzzled by his summing-up quote for this chapter:
"Regardless of the thickness of the wires and the high levels of
voltage, telegraph wires simply couldn't be continued indefinitely".
Now I would have thought the restriction was *exactly* due to the
limitations on wire thickness and voltage (ie the practical problems
with manufacturing telegraph cables and voltaic cells at that time).
Or am I doing Mr.Petzold an injustice, when perhaps there was some
other limiting factor ?
I have read somewhere that there were problems with insulation for
very long cables, is this perhaps something to do with it ?

It's simply a matter of a poorly-written sentence. It should read
something like 'could not be economically or practically continued
indefinitely'.

*In theory*, a basic telegraph circuit could be any conceivable length
*if* there is no limit placed on the size of the wire used nor the
battery voltage. But in the real world, there were very definite
practical limits to how thick a wire could be used, and how high a
battery voltage could be used. And the economics of the hardware used
were a major consideration.

The early transatlantic telegraph cables were thousands of miles long
and used *no* repeaters or relays along their route.

For a more detailed historical account of the telegraph and its
development, I suggest the book "The Victorian Internet"

73 de Jim, N2EY

William

May 4th 04 11:36 AM

(N2EY) wrote in message . com...
(Griff) wrote in message . com...
hi there everyone

I'm currently reading a book called "Code" by Charles Petzold which is
essentially a history and overview of computer technology, quite
entertainingly told. I've just read the section on telegraphs and
relays and am confused by something he has written.

He explains the basic principle of the telegraph, and goes on to show
with some simple Ohm's Law calculations that you can't extend the
length of telegraph wires indefinitely due to the loop resistance
etc., hence the need for the invention of the relay.

However, I am a bit puzzled by his summing-up quote for this chapter:
"Regardless of the thickness of the wires and the high levels of
voltage, telegraph wires simply couldn't be continued indefinitely".
Now I would have thought the restriction was *exactly* due to the
limitations on wire thickness and voltage (ie the practical problems
with manufacturing telegraph cables and voltaic cells at that time).
Or am I doing Mr.Petzold an injustice, when perhaps there was some
other limiting factor ?
I have read somewhere that there were problems with insulation for
very long cables, is this perhaps something to do with it ?

It's simply a matter of a poorly-written sentence. It should read
something like 'could not be economically or practically continued
indefinitely'.

*In theory*, a basic telegraph circuit could be any conceivable length
*if* there is no limit placed on the size of the wire used nor the
battery voltage. But in the real world, there were very definite
practical limits to how thick a wire could be used, and how high a
battery voltage could be used. And the economics of the hardware used
were a major consideration.

The early transatlantic telegraph cables were thousands of miles long
and used *no* repeaters or relays along their route.

For a more detailed historical account of the telegraph and its
development, I suggest the book "The Victorian Internet"

73 de Jim, N2EY

Another bit of history, I recall seing in a historical drama, Chief
Hiakowa sending his braves out to cut the lines to Ft Bliss. If the
wires had been thick enough and the voltage high enough....

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