So, your electrical signal has crawled through a thousand miles of cable under the sea, and emerged, breathless, in need of regeneration.
Once you see what was done, you can see that it was genius and, as the best ideas often are, simple. If you know when each bit (here representing a dot or a dash) is going to start, you can then make a reasonable guess as to what the original bit was. Provided there is a quite a big difference between the signal level for a dot and a dash, you should be able to regenerate the signal accurately. Regeneration hinged on knowing exactly when each bit started…
So, what could be used to reliably keep time in new electric Victorian world? A motor, that’s what. Use a clock to produce a pulse of electricity to drive a motor round and then everything could be synchronised, like the steam-powered factories that used belts to drive the machinery – only this was a pulse that drove everything in unison.
The dotted lines represent the pulses that are synchronised across the whole telegraph network, from master clocks at each relay sending/receiving station. The clocks were themselves synchronised to all the others using signals sent at the beginning of the day. There was also a speed adjustment on the interpolator to allow the speed of its motor to be tweaked to ensure absolute precision. Once you were synchronised, it was all straightforward.
You know when the character is supposed to start because your master clock tells you. You wait for half a turn of your motor – this puts you right in the middle of the incoming bit.
You then ask the question – is this signal above or below the reference (plus or minus a few microvolts to allow for noise)?
If it is above, you set a high voltage (usually 100 Volts) on your outgoing cable.
If it is below, you set a low voltage (-100 Volts).
Bingo! One regenerated signal now able to crawl through the next bit of wire.
This was all done using a motor and relays. If you are familiar with Terry Pratchett’s book “Going Postal”, you may recognise a distinct “Clacks” feel to this. The thing is, this was the start of the idea of long-distance near-instant communication being made real. It was also the beginning of the rise of the (electric) machines. Operators, previously required to re-key the messages were now replaced by wires and electrons. And it turns out, wires and electrons were hopeless at sports. On Ascension Island, so few engineers replaced the 30 or so operators, that team games had to be ditched in favour of singles tennis.
A new age was dawning, where the world was becoming connected, where information would be the new empire to conquer. At the heart of this revolution was, at least to begin with, the humble electric motor.
With huge thanks to John and Ravy (sorry to have misspelt your name here!) and, indeed, everyone who helps run the Porthcurno Telegraph Museum.