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In a parallel reality, what is stopping a contemporanean (from 1940 to 2020 alike tech) nation from jamming its enemies to hell and back?

A nation finds itself at war with another nation, what is stopping the agressor or defender from jamming all frequencies in the other nation with very potent and directive antennas (other than energy shortage)? The technology is there.

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    $\begingroup$ If you are jamming all frequencies you are also jamming your own communication. $\endgroup$
    – John
    Jun 19, 2022 at 11:08
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    $\begingroup$ "Jamming all frequencies" is only possible in the immediate vicinity of the jamming device. As frequency increases, radio waves behave more and more like light, with the effect that the curvature of the Earth acts as a shield. Already ultra-short waves (= FM band, tens of megahertz) and gigahertz waves (= mobile phone bands) cannot really be jammed on the territory of the enemy by jamming devices on your own territory. (Unless we are speaking of very very small countries.) For example, Russia cannot jam mobile phones in western Ukraine, regardless of how much they would like to. $\endgroup$
    – AlexP
    Jun 19, 2022 at 12:04
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    $\begingroup$ @4.1.2.22.4.18.0 Why energy shortage isn't already enough to answer your problem? In strategy... Well almost all domains in fact, energy costs is a crucial factor to do something or not. The fact it's not that important is an important thing you need to explain before we can answer, as there's a big hole in there. $\endgroup$ Jun 19, 2022 at 16:21
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    $\begingroup$ Try remotely jamming fibre optics. $\endgroup$ Jun 19, 2022 at 17:50
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    $\begingroup$ VTC because "Why would X?" questions are too often about the story and not the rules of the world (see Seeking community consensus about "Why would X lead to Y?" questions). It is unclear in your question whether you're suffering from writer's block (an off-topic storybuilding problem) are are unable solve a worldbuilding problem. Worse, there's a MASSIVE difference between 1940 (analog AM radio) and 2020 tech (digital cell phones & microwaves). That's way, way, way too broad. $\endgroup$
    – JBH
    Jun 19, 2022 at 20:09

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Jammers are blindingly obvious targets.

Simply put, a jammer involves devices that emit large amounts of electromagnetic radiation to drown out enemy transmissions within the frequency bands of the emitted radiation.

This makes them extremely obvious targets, since any enemy worth jamming will also be able to make equipment to detect the source of the jamming - all they'll need is a directional receiver. There's no way to hide a jammer while it's active, since the means by which it operates is also the key to detecting it.

As a result, once jammers are activated, they're likely to be deactivated shortly afterwards by radio-guided missiles.

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    $\begingroup$ Just imagine using a giant spotlight to blind enemies. Yes, they're blinded, but you literally cannot miss it, and people will just need to blindly shoot at that giant spotlight before it gets destroyed. $\endgroup$
    – Nelson
    Jun 20, 2022 at 4:22
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    $\begingroup$ @Nelson just as an alternative illustration - you "block" all spoken communication in the vicinity by shouting really loud. Jammers are the equivalent for radio communication. Yes, maybe people won't be able to hear each other but they'd know where the "jamming" is coming from. $\endgroup$
    – VLAZ
    Jun 20, 2022 at 7:40
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To make an analogy here... You can jam a conversation between two people by standing close to either one and yelling so loud that your victim can't hear their own thoughts. Who's using more energy? And who can easily end this foolery with a well aimed punch to the neck?

Now imagine that you wish to jam a whole city. You will need a lot of criers and they are going to clog the hospitals with their bruises and broken bones.

Now imagine you wish to jam a country.

Replace sound with radio that has a much longer range, and the enemy will invest in rockets and missiles that fly towards radio sources.

Also you jam yourself when you jam others, be it with sound or radio.

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  • $\begingroup$ Not if you use directive antennas or antennas with reflectors $\endgroup$ Jun 20, 2022 at 18:28
  • $\begingroup$ Even a directional antenna will need to be behind your front lines, so your troops will be jammed, too, even if your cities are not. $\endgroup$
    – Brianorca
    Jun 21, 2022 at 22:15
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Apart from the prodigious power output required and the oddities of wavelength physics which impacts how far particular frequencies of radio wave will travel?

The telephone, telegram, mail system & high speed courier/document delivery systems (in the 40's) to optical fiber communications & open air lasers (in the 2020's). Also its not just about raw power output. The technologies of both sides being more or less equal it should take relatively little time for the enemy to respond in kind, or alternately work out methods of evading/spoofing your jamming. Communication is no different to any other technology or weapon system. You build a better tank, someone else builds a better anti tank weapon. And on and on it goes!

There is NO perfect winning scenario where your technology works perfectly, always, in all situations. The enemy will always devise a countermeasure if the situation/threat is serious enough. That countermeasure may not be perfect, in fact it won't be . It just has to be good enough to 'mostly work' until the next new technique or technology emerges.

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I think resources could be better allocated to tapping into the frequencies and listening in on the enemy's communications. Radio is another vector for enemy intelligence landing in your hands.

In other words, is it worth investing in expensive (and vulnerable, as another commenter pointed out) antennas? Depending on how well military radio can be encrypted in your world, it may be more worthwhile to crack the enemy's code and exploit your newfound intel to, for example, counter submarine attacks.

You may want to look into the history of the Enigma machine. I'm no expert, but from my layman knowledge, the Enigma machine was repeatedly improved just as much as it was repeatedly broken by Allied forces.

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