I’m familiar with telegraphs and batteries, but also familiar with the inherent loss of voltage over long distances of wire. I don’t really know why or how, maybe the electricity just leaks out…so I’m apparently ignorant.
How did they get usable telegraph signals to travel many miles using only batteries of the day. How did they get usable signals to be transmitted across the Atlantic Ocean in 1866? I don’t think even today’s standard power cables of high voltage A/C travel that far. I assume, back in the 1850’s and 60’s they only had DC battery power.
Lord Kelvin did some of the design work - developing a very sensitive detection device, and insisting that messages be sent more slowly to prevent delays from confusing the signals
Transcontinental telegraphs were sent long distances by use of relays. Most relays were the simple electromechanical devices we still use today. An electromagnet would receive the incoming signal and attract a contactor that re-transmitted the signal using a local power source. Others were the occasional dude sitting in a telegraph office in the middle of nowhere who would receive and retransmit messages down one of many wires that came together in that office.
Ocean-crossing lines were a lot harder. The first ones tended to fail quickly and transmission speed was very slow. They worked initially by trying to push very high voltages as far as they could go.
It would take nearly a century before they could build transatlantic cables with built-in vacuum tube repeaters. (Though part of that delay is probably due to figuring out how to do transatlantic radio communication in the 1920s and 30s. For a while people assumed that cables would no longer be necessary. But the vastly increased bandwidth of a good cable quickly made radio comms obsolete, at least for civilians.
yes, I think I’ve heard of retransmitters, but my experience with modern batteries and electromagnets seems to suggest a usable signal wouldn’t be transmitted through a mile of cable, or at best maybe a few miles. Having a retransmitter every couple of miles doesn’t sound practical…so somehow they were getting signals dozens of miles or even hundreds of miles without retransmitters.
Electrical signals do OK over miles of cable. Landline telephone works that way, at least between the telephone unit itself and the local exchange building. There are such things as twisting wires and choosing system impedances to minimize the loss problems.
Years ago in a university library I found an 1800s book on telegraph engineering sitting on the stacks in the electrical engineering section (not locked away in some vault). How quaint, I thought, pulling the book off the shelf and preparing to disdain the primitives who must have been so full of themselves writing it. I was met with page after page of high level complex calculus (and I mean in the X + Yi sense of complex), matrix math, and all manner of other intimidation.
One of the biggest problems with transcontinental telecommunication were the amplifiers.
Up until the late 1920s, the philosophy was to string together many amplifiers, and engineers went to great lengths to make the gain of each amp very high. But this resulted in noisy and nonlinear amplifiers. The invention of negative feedback by Harold Black revolutionized telecommunication.
Early undersea telegraph cables didn’t work so well. They actually had to change Morse Code to accommodate the limitations of the cable. The first Morse Code used extra long dashes in some places. To make the cables work, they used one polarity for dots, and the other for dashes and received with a recording galvometer…so a long dash looked like two dashes. The dual polarity also balanced out any galvanic corrosion if the cable got damp.
The new code, with only dots and dashes, survives until today, known as International Morse, because it was first used between England and France, on the trans-channel cable, and soon became the standard for A1 radio communications.
The older code was entrenched with Western Union, and Railroad telegraphers, so it survived a long time as “American Morse.” Today it is only used for nostalgia’s sake by a few collectors of old telegraph equipment.
Is there anything to do with scale that aids? For example, the surface area to inner volume of a thicker cable is so much improved that you suffer less electrical loss by a significant factor?
My dad’s dad was slightly a railroad man (we still had a lot of company advertising around the house when I was young) and he called it “railway morse”.
According to my dad, a big difference was that in Railway Morse, the sound you heard was the make, and the break (click-clack). A dot had a short interval between the make and the break, a dash had a long interval between the make and the break. This was a DC system, and pre-dated the use of oscillators to get a tone.
It wasn’t until even later that co-axial cables were thought of, the primary value of which is better control of the dielectric. There wasn’t any understanding of skin-effect in copper cables.
Most of the Energy flows in the area outside the wire. The insulator. The Dielectric. When the very first transatlantic cables were installed there was little if any understanding of this, and most of the transmitted energy went to energising and de-energising this electro-magnetic field. The first solution was to boost up the voltage. That was a disaster. The next solution was t o t r a n s m I t v e r y s l o w l y . Which worked, but in todays money they were charging $1000 per word. Inductive loading was what brought the signal distortion down to where resistive effects were more important than smearing.
In modern high-voltage power transmission systems, the outside diameter of the cable bundle is important. For the original transatlantic cables, they had a lot of other things they had to understand and fix first before discovering second-order effects had any benefit.
The whole point of Morse’s system (as he saw it) was that it provided - on the tape - a written record of the message and at first any clerks found reading the messages by listening to the printer were instantly dismissed.
Assuming AC voltage, there’s also a problem with capacitive coupling between the wire and the surrounding earth (or the earth below, if the cable is up on utility poles - or the surrounding seawater, if we’re talking about a submarine telegraph cable).
[spoiler]Two sisters, one blonde and one brunette, inherit the family ranch. Unfortunately, after just a few years, they are in financial trouble. In order to keep the bank from re-possessing the ranch they need to purchase a bull from*a stockyard in a far-away town so that they can breed their own stock. They only have $600 left.
Upon leaving, the brunette tells her sister, “When I get there, if I decide to buy the bull, I’ll contact you to drive out after me and haul it home.”
The brunette arrives at the stockyard, inspects the bull, and decides she wants to buy it. The man tells her that he will sell it for $599, no less. After paying him, she drives to the nearest town to send her sister a telegram to tell her the news.
She walks into the telegraph office, and says, “I want to send a telegram to my sister telling her that I’ve bought a bull for our ranch. I need her to hitch the trailer to our pickup truck and drive out here so we can haul it home.”
The telegraph operator explains that he’ll be glad to help her, then adds, “It’s just 99 cents a word.” Well, after paying for the bull, the brunette only has $1 left. She realizes that she’ll only be able to send her sister one word. After a few minutes of thinking, she nods and says, "I want you to send her the word “comfortable.”
The operator shakes his head. "How is she ever going to know that you want her to hitch the trailer to your pickup truck and drive out here to haul that bull back to your ranch if you send her just the word “comfortable?”
The brunette explains, “My sister’s blonde. The word’s big. She’ll read it very slowly…
com-for-da-bull.”[/spoiler]
Here’s a long-but worthy article published in Wired magazine back in 1996 that talks about the history of undersea data cables, going back to the first telegraph cable ever laid and covering the latest (at the time technology) and all of the various challenges involved in installing and using them: