Simple low power spark-gap transmitter

[petert]

Hello, I found this interesting video on youtube that shows how to make a simple spark gap transmitter.



I wonder how many windings such a coil should have, ideally?
And how does it create a high voltage? The video is quite vague about this.

[m3vuv]

you do know if your licenced or not these are illegal to use,maybe a good way to wipe out most hf bands and upwards,please dont take it beyond the thought stage.

[petert]

The example only has a range of a meter, or a few at most, so it shouldn't disturb anyone

Others even work with piezo lighters only, so it shouldn't be a problem.

[petert]

It seems a normal switch, from a lamp or wall mounted switch is already enough to generate a pop in an AM radio (without changing anything).

The remaining question is still, why would a quickly loading and unloading coil as in the video generate a high voltage?

Is it merely inductive kickback (when the circuit is broken due to the metal sheet being attracted by the coil) or is there more to it?

Is this simulation and appropriate model for the spark gap in the video?:
https://www.falstad.com/circuit/e-inductkick.html

It would seem to me that the two metal parts (the sheet of metal and the nail in the wood) would form a capacitor, while the sheet of metal is pulled away due to the attraction of the coil.

Just that it arcs additionally, which would cause a capacitor to be damaged, but in the case of a spark gap, would just cause a fast discharging.

Is that correct?

[@rt]

Nothing new. You can make the same thing with nothing more than a relay.
The switch and the coil are both inside the relay.

Yes it’s magnetic field collapse in the coil from rapidly toggling the switch.

You can strike, and run a pigtail neon with it.

[petert]

I finally made a coherer from copper-nickel filings (cupronickel) that are in a small flexible plastic tube terminated by two screws, one at each end, touching the filings in the middle.

The piezo-element from a piezo-lighter was taken out, and two cables were connected to it, so that a spark could be created where the two cables' ends almost meet.

This setup was enough to make the coherer detect the signal up to about 1 m away.

I am experimenting with antennas to see the effects on range.

I'd like to see what the generated signals look on a scope/spectrum analyzer, but I am afraid the generated voltage might damage it.


I have no video or pictures, but similar setups can be found here:



making an ignition coil:

[tkamiya]

In early radio days, transmitters were literally generators spun really really fast.  Even earlier, spark gap was used.  High voltage between gaps, or inductively induced, like you are doing or some other ways.  Coils store energy.  When it is suddenly released, it comes out as high voltage. 

As to legality, what he has is nothing more than a buzzer.  Unless he connects antennas to it, it won't go too far outside of his room or house.  Perfectly legal.

DO NOT connect it to spectrum analyzers or even oscilloscopes!  You can connect a short piece of wire in such instruments and place it few meters away.  There is enough energy saved in that coil to blow away the FET or whatever front end you might have.

[German_EE]

I strongly suggest that these experiments should cease, before the Bundesnetzagentur have words, words such as 'bitte komm mit mir zum Polizeiauto'

[iMo]

Funktechnik, Telefunken, Funkamateur, Rundfunk, Rundfunkgerät, Sprechfunkgerät, Funkausstellung Berlin..
Funk means "spark" - thus the experiments with spark-gap transmitter are pretty popular in Germany, it seems..

This type of radio emission has been prohibited by international law since 1934.

https://en.wikipedia.org/wiki/Spark-gap_transmitter

[petert]

I strongly suggest that these experiments should cease, before the Bundesnetzagentur have words, words such as 'bitte komm mit mir zum Polizeiauto'

That wont happen, it's not even detectable in the next room