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Is it possible to jam the jammer signal, to disrupt its jamming of the owned RF signal?

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  • $\begingroup$ It is illegal to cause intentional interference, period. $\endgroup$ – SDsolar Mar 23 '17 at 8:53
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This would be something like active noise cancellation and depending on the nature of the source could be somewhat possible.

However, it is not a trivial task.

If you imagine trying to cancel out an unmodulated carrier wave, with both the unwanted transmitter and a single receiver you are trying to "unjam" in fixed locations, you simply would need to transmit your own unmodulated carrier at some particular amplitude and phase, such that your "unjamming" signal and the jamming signal cancel out at the receiver.


However, if the jamming signal is changing unpredictably, you'll need to be able to mimic it — only 180º out of phase — quickly enough to maintain the cancellation at the receiver.

Furthermore, if you are trying to "unjam" multiple (and perhaps mobile!) receivers the problem becomes much harder still: now you have to cause this destructive cancellation not just at a single fixed point, but at multiple points simultaneously. Sort of like causing a "picket fence" effect to the jamming signal, but your job is to control things so the "dead spots" land exactly where you want!

Basically you're having to design an antenna array with deep nulls in all the right places. To make matters worse, before you can drive those elements of this antenna array which are under your control (at least one won't be!), you're also having to reconstruct the original transmission to feed into your part.


Can you do this more simply?

Well, if you can arrange to unjam the interfering signal directly at each receiver, you avoid the need to deal with all the "antenna array" stuff. But then the problem boils down to really the same thing "noise blankers" and "DSP filtering" and whatnot are trying to solve already.

And if you can arrange to unjam the interfering signal directly at its source, well, then… bring some wire snips?

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A receiver's objective is to take some message which has had noise added to it, and recover from that the original message. Receivers need to do this even in the absence of jammers since natural sources add noise all the time. Jammers just add more of it.

In this sense, a jammer can't be "jammed". The jammer does not have the objective of recovering a message hidden in some noise, so there's nothing to jam.

That doesn't mean signals can't be made resistant to jamming, however. The game of jamming and counter-jamming is a game about information asymmetry. If the receiver knows something that differentiates the jammer from the legitimate transmitter then it can use that information. For example if a receiver knows the transmitter is to the North and there's a jammer to the East, then the receiver can employ a directional antenna pointed to the North.

Likewise, the more the jammer knows about the intended communication, the more effectively it can disrupt communications. For example, if the jammer knows that the communications are initiated on 146.52 MHz at noon each Monday, this is a lot easier to jam versus a situation where communication could take place on any frequency at any time.

There's no limit to how much or what kinds of information are relevant in this game. In military applications where malicious jamming is the norm they've been playing this game for a very long time. Simple frequency hopping techniques saw use in the First World War, and since then it's been an electronic arms race.

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While the other answer is all true and well formulated, let me take another approach.

One definition of "Radio Jamming" as given by the linked Wiki page is:

"any device that deliberately blocks, jams or interferes with authorized wireless communications"

And doing so would be in disregard of our Amateur Radio license conditions, and ethic, therefor we as licensed amateurs should not do this to begin with.

So the question

"Is it possible to jam the jammer"

is an ethical question.

I believe that jamming a jammer will make you a jammer. Therefore we should not try to do this either.

  • Don't jam
  • Don't jam the jammer

Some will jam, so then you spin the dial and move somewhere else, we have plenty of spectrum to play with.

[EDIT based on comments]

Some further explanation is needed:

I deliberately did not take a "legal" definition of "jamming" as the wording of legislation could differ between jurisdictions. However, we can probably all agree that "jamming" as a term will be interpreted by most people as a "deliberate action to disrupt communications".

[opinion] I certainly believe that across the different jurisdictions, the legislation and license conditions will include some wording that "deliberately interfering with signals" is not allowed. [/opinion]

If a HAM is "disrupting communications" due to malfunctioning equipement, or he simple does not know there are communications on the frequency due to the fact that he doesn't receive the communications at his end (due to propagation or his setup/equipment) then this is QRM, and I would not call it "jamming". In such case you would try to solve this in a more HAM-like way, trying to contact the operator to inform him of the situation.

If the "jamming" is causing life threatening situations, which you can only think of a few-and-far-in-between situations on Amateur frequencies/allocations:

[opinion] Then I would still believe that "jamming the jammer" is not the correct action to take.[/opinion]

One could indeed argue that "jamming a jammer" is not "jamming an authorized signal", in which the ethical approach of my previous answer will still prevail as my opinion on what the expected behaviour of a licensed Radio Amateur shoud display.

Furthermore the OP uses the following wording "to disrupt its jamming" which indicates a deliberate action on the part of the jammer-of-jammers. [opinion] Ethically this is still the wrong action [/opinon]

I have never heard, read or otherwise, something like a "jammer of jammers" to exist in the licensed Amateur Radio world. "proof me wrong"

I stand by my first answer:

  • Don't jam
  • Don't jam the jammer

And add:

  • In life threatening situations, follow escalation and notification to official institutions. Try to help with the communications which are jammed by relaying the message another way. But do not jam the jammer, as you may risk that your anti-jammer-jamming is actually jamming for the original communications.

And maintain the final:

  • Spin the dial, don't give a "jammer" the satisfaction of engagement.

If the OP was in reference to "jamming outside Amateur Radio frequencies" or "the technical details on how to jam or anti-jam" then one could consider that this could/would be a topic for:

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  • $\begingroup$ I somewhat agree with the general idea of your answer, but you might do better to rely on e.g. FCC or other similar body's legal definition of things like "malicious interference" or "authorized transmission" rather than simply an encyclopedic or dictionary definition. For example, going with the Wikipedia definition "interferes with authorized wireless communications" one could argue that the original jamming wasn't "authorized" so you aren't "jamming". But maybe that conflaties legal ("authorized"/"unauthorized") with ethical ("jamming"/"not jamming"), and you did say you're talking latter. $\endgroup$ – natevw - AF7TB Aug 31 '16 at 20:44
  • $\begingroup$ …I guess maybe what I'm really trying to say: there's the legal question, which should be answerable by consulting the relevant regulations. If you want to focus on ethical, instead, then maybe there are times when it is okay to "unjam" — maybe the jamming was unintentional and you're just helping fix, maybe the jamming threatens life/property/goodwill, maybe you've been appointed to be a "jammer of jammers", etc etc. $\endgroup$ – natevw - AF7TB Aug 31 '16 at 20:47

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