Aviation radio is AM instead of FM.
End of article.
But seriously, if you’re curious to know why this is actually the case keep on reading.
One of the main reasons why AM instead of FM is used is rooted in history. When aviation bands started a long time ago it was simpler and less expensive to make equipment for AM – not to mention more reliable. AM isn’t as dependent on outside conditions and is simpler to get a signal out of in terms of equipment.
To transmit AM all that is required is to add a transformer and audio amplifier to an existing single-frequency transmitter. To receive, just make sure that the receiver has a wide enough bandwidth. That’s it. Job done.
Trying to change to FM would be hugely impractical and arguably near impossible too. Sit down for a second and just think about how complex and time-consuming it would to even attempt this. You only have to recall what happened when railroad communications changed to see that doing this for aviation just wouldn’t be feasible, especially as it would be on a much, much larger scale.
The capture effect is when a stronger signal suppresses a weaker signal. You can see why this would be a problem in aviation where a nearby aircraft could inadvertently override ATC. With the use of AM in aviation, multiple signals transmitted on the same channel can be heard.
AM signals can travel greater distances than FM. Range depends on wavelength, so AM with their longer waves (lower frequencies) can pass through obstacles with ease, resulting in greater range. Another reason is that the longer waves are reflected in the stratosphere, which again results in greater range. The top (and most expensive) handheld aviation radios tend to have better range by design.
FM performs better where a wide spectrum of audio is required. Listening to music in AM isn’t much fun, for example. Considering that aviation communication is focused on the human voice, FM therefore isn’t necessary.