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I am trying to understand how basic electromagnetic communication works.

From what I understand, spark-gap transmitters were the first wireless devices made by man. A couple of circuits I found online involve high voltage devices that create a spark across a small gap (electro boom.)

However, I came across videos from two gentlemen with similar circuits that do not use high voltage. Adding a link here for reference.

Basically, it involves an electromagnet that disconnects a circuit when powered, and then when power gets reestablished circuit reconnects, and the cycle repeats. Is this feasible for creating EM wave? Is this a spark gap or something else.

Reference: https://www.youtube.com/watch?v=izCV1WrPFds

JRE
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Mat
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    What is the frequency of the connection and disconnection? Is there any mechanism for frequency selection? Are the electric and magnetic fields confined or allowed to spread out of the device? Please add a circuit diagram (taken from the video if necessary). In the Spark gap setup, the capacitance and inductance of the loop provides frequency selectivity. – AJN May 24 '21 at 16:52
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    Here's a better video on explaining and demonstrating a spark-gap transmitter: https://www.youtube.com/watch?v=SnKKj2bonAI – ErikR May 24 '21 at 17:05
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    Please, pretty please, don't use spark gap transmitters in 21 century. A lot of people will hate you big time. – fraxinus May 24 '21 at 17:07

1 Answers1

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That circuit works just like old door buzzers worked -- it's just a simple relaxation oscillator.

Any oscillating electric circuit creates electromagnetic waves. The buzzer creates EM waves on a large frequency spectrum which is why it can be picked up by the radio.

There are two problems with using this circuit for communication:

  1. Radio transmitters today are required to transmit on a very narrow frequency band which this device doesn't and therefore it wouldn't be approved by the FCC (or your local regulatory body).

  2. The reception range is very short. If you went to the next room you probably wouldn't pick it up.

ErikR
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