Our traveler appears in a medieval world that with knowledge of the modern world. Maybe he has a copy of wikipedia in his head. He decides to take over the world but he does not take the normal path of gunpowder. Instead he invents long range communications with some sort of wireless telegraph. Could he do this in the 1500s or so.

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    $\begingroup$ As a clever and brutal Duke in the 1500s, I'm pleased by this idea. My spies discovered the use of the magical-message-box, and a few of my agents 'acquired' one during a dark night...along with it's operators. I have discovered that the threat of flogging encourages the operators to let me listen to the innermost counsels and secret messages of this time-traveler. Turns out that many folks will pay me a lot to know what those innermost counsels are. $\endgroup$ – user535733 Mar 6 at 2:27
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    $\begingroup$ They already had gunpowder and cannon "in the 1500s or so". They even had some really big guns. And knowing all Wikipedia by heart won't tell you how to build a working radio. His only chance to do it is to prepare beforehand, in the 21st century, a full technological chain which could be implemented in the 16th century, and take with him a small army of technicians and a lot of gold. $\endgroup$ – AlexP Mar 6 at 2:40
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    $\begingroup$ A radio seems hopeless. A spark gap transmitter might be doable. But it isn't a great way to become powerful, it will require quite a bit of work. $\endgroup$ – Zwuwdz Mar 6 at 4:09
  • $\begingroup$ Spark gap transmitter sounds right. And they don't seem complex. Why is it a lot of work? $\endgroup$ – Tommie Jones Mar 6 at 11:34

Oh, yes, easily.

Creating wire by various different methods has been around for at least 4000 years (for jewelery and decorative purposes).

  • A sheet of metal was cut into a strip and drawn through progressivley smaller holes in beads to smooth and elongate it. (A a big sheet and a helical strip could produce great lengths without the need for joining). Soft and conductive metals like gold and silver are particularly suited to this, or in-a-pinch tin would serve.

  • Two sets of orthogonal hammers were used on bars of metal to form square wire.

  • Insulation was then simply wrapping in cloth and coating in any of the available natural resins and thermoplatics (wax, rosin, shellac, tar etc.).

The generation of radio frequency waves could then be achieved by creating a disk on a spindal, which would either have fixed magnets (naturally occuring haematite) around the circumference, or slots - the alternating of slots and metal when spun in a steady magnetic field would act as dipoles, with a coil nearby to pick up the alternating field. This would be spun at high speed until the desired frequency was achieved (as in the Alexanderson Alternator). This could be geared (available since circa 400 BC) such that a slave would power it - perhaps working to the rythym of hummed melody to keep the output speed the same.

To modulate the transmission for voice, a magnetic amplifier would then be used (essential in the early days of radio pre-valves).

The aerial would not need to be miles long, just wound around a ceramic in the propper way to form a tuned loaded coil.

The microphone would be a simple carbon-granule affair behind a basic diphragm - like those used in telephones before the 1980s. (charcoal won't do, it does need graphite).

The reciever The principles of using naturally occuring semiconductors in coal to create the heart of a crystal radio are well known. An adjustable air capacitor would then be used to tune reception.

The speaker would be a thin sheat of cleaved quartz (or other piezoelectric material) with gold leaf to apply the electrical signal across it making a crystal speaker.

You are now free to conquer the know world and re-draw the maps as you see fit.

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    $\begingroup$ ++ I like it. Not that I totally agree with all, for instance 'thin shee of cleaved quartz' and 'air capacitor' will require precision manufacturing. And that 'air capacitor' will require materials that don't corrode - otherwise the capacity goes astray one day to the next. And the 'spun at high speed until the desired frequency' will require enough speed control to keep on the agreed transmission frequency - I'm afraid humming a tune will allow too high a drift over time. And the power required for a long-wavelength transmissions is beyond "just use a horse walking in circles". $\endgroup$ – Adrian Colomitchi Mar 6 at 6:31
  • $\begingroup$ Quartz can literally be cut along it's planes of cleavage - that's ancient tech. The whole point od an adjustable air capacitor is that it should be adjusted every time, as atmospheric conditions (pressure, moisture temperature) vary over time, so I don't see the issue. I guess for long distances, relay stations would be needed. Frequency control could be an issue I agree, but with crude (broadly tuned) recievers, you could I suspect get through. I realy want to play with this equipment now to see how it works. @AdrianColomitchi $\endgroup$ – Tantalus' touch. Mar 6 at 7:06
  • $\begingroup$ Now, look, I'm not saying that's theoretically impossible to replicate the more modern technologies in earlier historical times. What I'm saying is that: practically replicating those technologies to enough degree of precision and control and developing all the technologies that support your technologies to the same degree of precision/control (you know? things you take for granted in modern times) is very likely to take longer than a human life, even if you do it faster by eliminating all the mistakes and delays that were encountered during their actual historical progression. $\endgroup$ – Adrian Colomitchi Mar 6 at 7:14
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    $\begingroup$ I realy want to play with this equipment now to see how it works. I'd be very curious if you actually hands-on do it. I had a DIY experience for a much simpler case and the things came up mediocre and unreliable as results. And when you want 'production/exploitation environment' and your work (perhaps a life-long work) needs to function in order for you to derive the take over the world type of benefits, unreliability is a killer. $\endgroup$ – Adrian Colomitchi Mar 6 at 7:26
  • $\begingroup$ I agree, at the moment I'm just an "armchair dictator". If I ever get the time to I'll start hitting quartz and post about it somewhere. (A good old copper coated fibreglass board, etch resist pen and ferric chloride are my friends. I've never tried using transfers, good link though, interesting site) This comment thread'll probably get deleted soon for being too "chatty". BTW, tooth enamel is apparently piezoelectric, ever hear the radio through your fillings? @AdrianColomitchi $\endgroup$ – Tantalus' touch. Mar 6 at 7:44

Short answer: no, I don't believe so.

Science and technology are two different things. Letting aside uniform width conductors for coil wires, magnetic materials for coil cores, etc, you do need at least vacuum tubes.

Which do require technological advancement in glass making (to match the dillation of glass and electrodes) and refractory metals for the electrodes (tungsten) and precision mechanical works.

Sometimes I think Edison's bulb was revolutionary not because it brought the electric light, but because it showed how to build a fillament that doesn't burn when it gets to high temperatures.

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