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I am looking for a good reason to make radio communications on a planetary scale unfeasible or impossible. Short-range use is acceptable, but no transmissions should make it to orbit or over the horizon line. Hints on specific type and features of an atmospheres are welcome, as well as scenarios that involve no atmosphere.

First, before people start yelling "solar storms!" just bear in mind that even the craziest geomagnetic phenomena might not be effective against lower frequencies traveling long distances.

How this question is best answered depends on the forms of communication we're talking about. If you limit your technology to specific forms of communication (i.e., what frequencies we're dealing with), the constraints are easier to define, and it's easier to give you more specifics. (Microwave frequencies behave differently than FM, etc.)

No transmissions should make it to orbit or over the horizon line.

As your question implies, you are already aware that some forms of radio waves will reach distances beyond the line-of-sight of the transmitter because of how they "bounce" off the ionosphere. But they can also travel long distances as ground waves. This Wikipedia article has some good info.

Generally speaking, in theory, I suppose if you had a ridiculously ionized layer of atmosphere, it could conceivably block most if not all signals from reaching orbit, so that solves half of your problem. (The science is a bit less simple than I'm making it sound, but that's the basic idea.)

As for the other half of your problem, I would consider using terrain as a way to limit your range. Bodies of water and rugged, mountainous landscapes absorb a lot of EM radiation.

Note also that some weather can actually work against you and improve the signal range.

A mars sized planet would be more difficult for radio because of the enhanced curvature of the surface. A planet with an atmosphere thick with metallic dust also bad.. especially if that meant frequent electrical storms. A planet with a weak magnetic field.. allowing solar particles to penetrate the atmosphere.. basically mars.. with a slightly thicker atmosphere.

What would make radio transmission unfeasible on a planet?

Fierce Geomagnetic Storms.

A non lower-atmospheric solution is a very active sun that releases more or less continuous flares which beat on the upper atmosphere - as they do on Earth in an eleven year cycle - but if the ones squirting out from your star are more or less continuous, then they'd fit the bill.

• There's the storm of March 9, 1989 which disrupted radio stations - some believed it had been done by the Russians and was the start of something more sinister (it was during the cold war).

Creative Commons Attribution-ShareAlike License: Wikipedia 2018.

• There's a nice chart on Wikipedia about their classifications and how big they get on Earth (a bit like earthquake classifications).




• There's a brief bit about potential effects on animals when it gets realy bad which may be worth noting.

To keep the signals from reaching space you would need a charged upper atmosphere that is strong enough to block most signals. This may result in some aurora borealis if my understanding is correct, but it's pretty set dressing at least.

The problem is that radio waves can travel through the ground too, so if you want to limit your communications range you need to alter the planets surface composition. Ever hear of Aokigahara? It's the place where Logan Paul screwed over his whole career. Well that place blocks cell signals because of the hill's rich iron composition. Make your planet rich in iron and that will fix most of your problems.

However, the signal might still bounce between the ground and atmosphere and the high charge might cause nothing but radio static everywhere, so some hand waving or contrivium may be in order.