I've heard many times said as an argument in favor of broadcast regulations that the radio wave medium (the atmosphere/ground) will become "polluted" if people send radio signals at whatever frequency and power they want. The signals might also cause "interference".

First, what is meant by signal pollution and interference? Do they mean the same? I think "interference" of signals can not mean that signals are colliding because radio waves pass through each other. Does it mean that electronic equipment is affected?

Second, if radio wave interference or pollution is the reason behind radio broadcasting regulations, how is this interference or pollution a problem with radio wave receivers? A radio wave receiver is tuned to a specific wave frequency, so should it not just ignore signals of other frequencies that aren't meant for it?

A radio wave receiver is tuned to a specific wave frequency, so should it not just ignore signals of other frequencies that aren't meant for it?

In order for a radio signal to carry information, it can't be just a single frequency. It must carry power over a range of frequencies. You can get some background on why this is so if you research the modulation property of the Fourier transform and the Shannon-Hartley theorem. Another question on the site addressing this is, Why is bandwidth, range of frequencies, important when sending wave signals, such as in radio?

Since useful signals need a non-zero bandwidth, you can't pack an infinite number of them into a finite bandwidth without them overlapping. Also, it measn when you tune your receiver to a specific frequency it must also pick up a band of frequencies around that center frequency in order to receive any useful information (like an audio waveform or the digital data carried over a wifi link).

If two signals overlap in their frequency spectra, then when you tune your receiver to one of them, you'll hear some artifacts or noise caused by the other overlapping signal. This is what is meant by interference.

Pollution isn't a technical term like interference. In the context that you described I'd take it to mean the effects of multiple interference sources when combined together.

• Worth noting, we get away with talking about radio transmitters operating "on a wavelength" because in many cases the bandwidth you need is far smaller than the central wavelength itself. For example, FM may transmit at 98.7MHz (98,700,000Hz) while the bandwidth of that signal while the signal only need about 60kHz (60,000Hz) to transmit the audio. For most layman purposes, we can get away with just paying attention to the center frequency and ignoring the bandwidth, but for topic like this we do need to pay attention to both. – Cort Ammon Jun 11 '17 at 16:07
• From the perspective of a commercial radio station, they sell advertising based on their coverage area. Without regulations and enforcement, you would have pirate stations infringing on that, and the result would be lost revenue for the station. From a consumer point of view, you'd have huge interference (pollution) problems where the station you want is blocked by the other station on the same frequency. When you get into frequencies used for business and public safety, the consequences could be MUCH worse. Radio recievers have a LIMITED capability to reject adjacent signals. – user103218 Mar 14 '19 at 12:39
• @user103218 Depriving people of advertising revenue isn't really a good reason for regulations unless you can show that the advertising-supported stations contribute more to society overall than the "pirate" stations (which wouldn't be pirate stations if they were legal, now would they?). – user253751 May 26 '19 at 22:01