AM and FM Radio Explained - GoTechTalk


Sunday, August 5, 2018

AM and FM Radio Explained

Maybe it's just because I'm old, but even though Spotify podcasts and other forms of audio streaming seem to rule the day there's just something comforting about the simplicity of turning a knob on the radio and listening to what's happening on the airwaves.

Even in the digital age radio has maintained a fair amount of popularity since the first public broadcasts in the early 20th century, but since radio has been around since long before we had things like digital decoders that turn electrical impulses into music. how simple cheap radios know how to convert an electromagnetic radio signal into let's say a basketball game or a weather report or uh you know Justin Bieber's greatest, anyway AM radio broadcast showed up before FM. So we'll start with those an AM station will broadcast a signal at a constant frequency but will add the sound wave representing the actual audio to that base signal it's also called a carrier wave resulting in the height or amplitude of the wave changing accordingly this is where the term AM comes from as it stands for Amplitude Modulation you can get your radio to playback this signal as actual music or dialogue by tuning it to whatever frequency of the station that you're looking for broadcasts at this makes our antennae resonate at the frequency and ignore everything else in the air so very simple radio tuners are actually little more than coils of wire how many turns of the wire will determine what frequency you're picking up cool right the antenna actually creates an electrical current that corresponds to the radio signal this current is sent to other parts of your radio that filter out the irrelevant parts of the signal and send it to your speakers or your headphones as changes in voltage which drive those speakers and produce sound, it's actually pretty remarkable that this is all done without any digital decoding by something like a CPU it's a completely analog process that made it possible for news music and entertainment to stream into homes decades before the internet or even TV.

FM broadcasting works somewhat similarly though with FM it's the frequency of the signal that gets changed hence the F in FM. FM radios have a special transformer inside them that basically sits idle as long as exactly whatever frequency your tunes to hits your antenna but once it detects a small change in that frequency it outputs a voltage that makes your speaker's emit a certain sound so let's say you're tuned to 99.5 FM on your dial  since FM works by using very small changes in frequency to carry a signal you are actually tuned to signals just above and below 99.5 megahertz which makes that transformer send the voltage to your speakers now although this process makes FM more complicated to engineer than AM you often get a much clearer higher-quality signal FN is less susceptible to interference as well because interference often manifests as amplitude spikes and AM radio would see these spikes as actual sounds to produce and it would end up coming out of your speakers while FM cares about variations in frequency rather than amplitude, so when FM radio can just ignore that type of interference and the music you're listening to will come out sounding just as clear and angry as ever.

FM also has the advantage of having much higher bandwidth in AM due to the mathematical properties of frequency modulation this allows for lots of wiggle room in the signal to create more sounds more accurately making FM the clear choice for music while AM is often just fine for stuff where high fidelity isn't a big deal such as talk radio, but if FM is so superior then why do AM stations seem to have so much better range well it's because AM wavelengths are much longer meaning that they can move more effectively following even the curvature of the earth and deal with obstacles like buildings whereas you can quickly lose high-frequency FM signals if you start putting stuff in the way, AM frequencies also allow signals to cause free electrons in the ionosphere to oscillate at the same frequency as the radio wave that hits them meaning that AM signals can actually reflect off the upper atmosphere, at night there are more free electrons hanging out in the sky which is why you can sometimes hear AM stations from hundreds of miles away after the Sun Goes Down as opposed to FM which tends to go right through the atmosphere of course this may not seem impressive when the Internet allows you to listen to high-quality digital broadcasts from the other side of a world no problem but good old analog radio still has the distinct advantage of only requiring a ten-dollar receiver with no subscription fees and very high ease of use especially for people who might not be terribly tech-savvy and of course your radio will keep working even if your internet connection goes out, sometimes simpler is indeed better.

Alright, guys, that's the end of the blog, thanks for reading the whole way through if you enjoyed this blog please share it with someone who would be interested and leave a comment, Thanks for reading guys.

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