What is the difference between AM and FM radio and why is FM more popular?
In: Technology
AM sounds poorer than FM, that’s mainly why FM is more popular.
AM has longer range, FM shorter range.
Edit: I’m struggling to simplify and explain the modulation differences. lol. Hopefully you get a better answer.
Also, with what frequency or frequenies is AM delivered? I get the amplitude side of the house but if it’s not a singular number wouldn’t if be AFM, or A&FM?
There are technical differences in how FM and AM modulation work. The result is the sound quality is better for a longer distance but then quickly go to no reception at all. AM gradually decreases in sound quality.
Because of the amount of spectrum given to AM and FM stations even in good reception, there is a huge sound quality difference. AM have 10kHz spacing between stations in the US, 9kHz in some other places. The signal contains a mirror image of itself so the sound is limited to 5kHz and 4.5kHz. Humans can hear sound up to around 15kHz for adults and 20kHz for younger people. This mean if you broadcast music on AM radio it will never sound very good. This not a fundamental problem with AM modulation but one of what part of the spectrum is available for AM radio.
FM has 200kHz available, it make it possible to fit a mono signal of 15 kHz and tow channels for stereo and still have space over.
AM modulation is easier and cheaper for transmitters and receivers. It was the first type of broadcast radio. It transmits at 0.5 to 2 MHz range, it results in a long-range for the station, the drawback is there is only enough spectrum for 10kHz per channel. The longer range is not always an advantage if means the distance between two station that sends of the same frequency needs to be very long.
FM is a newer technology with more complicated transmitters and receivers, The frequency range is usually 87.5 to 108.0 MHz the larger frequency range makes it possible to give each station a large part of the spectrum. It alos reduces range but that means the same frequency can be reused at closer distances.
The cost part is more relevant historically than today. FM broadcast spectrum was dedicated for that use in 1945 in the US. Even so, it was not until 1960 it became common in the US. With modern electronics, the cost of receiving both is equally low. I am not sure if there is a transmission cost difference.
You could transmit AM radio at the FM frequency or in other bands. You could then give the station a larger frequency range so the sound is better with good reception. It has not been done because FM is even better for sound quality. If you put FM radio at the AM band you would need to reduce its sound quality to or fit fewer stations is the available spectrum.
So today the main difference of AM and FM radio is sound quality and how large area the signal can cover from a single broadcaster.
AM sound can be heard at long distances but the quality is very unreliable. It might cut in and out like a phone with bad reception.
FM sound is that good quality that is reliable and mainly available in larger, more populated cities. Once you drive out of range, it’s just gone completely.
Both formats are based on approximating a sound wave, which is a kind of sine wave, with radio waves, which are also sine waves.
AM stands for amplitude modulation. That means that the amplitude of the radio waves is increased and decreased to approximate the sound wave.
FM stands for frequency modulation. That means that the frequency of the radio waves is increased and decreased to approximate the sound wave.
AM waves, being of relatively low frequency, will hug the surface of the Earth more, so they can be received over longer distances. AM transmissions also have more static and don’t transmit music that well, so it is an ideal platform for talk radio, news, etc.
FM transmissions have shorter range but much higher fidelity in terms of frequency response, low distortion, etc., so FM is the preferred platform for music.
In the mid 20th Century, there was a titanic battle between the two broadcast formats.
I’ll attempt a slightly more ELI5 explanation.
“Modulation” in this case, is basically a way to encode an audible signal into a signal beyond the range of human hearing.
AM or Amplitude Modulation is encoded in such a way that the decoder (a radio or similar device) rebuilds the original audible signal based on the changing amplitude (think “loudness”) of the broadcast signal. This is cheaper and can be transmitted further than an FM signal, but the main downside is that it isn’t as robust. If the signal has to go through a wall or something to reach the radio, the signal can be attenuated (made “quieter”), which will change the decoded audio. AM tends to be used for talk radio rather than music because of this.
FM or Frequency Modulation, on the other hand, is encoded in such a way that the decoder rebuilds the original signal based on the changing frequency (or pitch, if you’re musically inclined) of the broadcast signal. This is more robust than AM, because as long as the signal is strong enough for the radio to pick up, the frequencies will be the same, and therefore the signal will be reproduced correctly. This is why FM tends to be used for music (FM stations also have more bandwidth so music sounds better than it would on AM, but that’s somewhat outside the scope of this post).
AM travels very far but has less stuff in it so it doesn’t sound as good.
FM has a lot of stuff in it so it sounds very good but it can’t go too far.
1 AM station could cover the same area as a lot of FM stations, so there’s more FM stations than AM.
Imagine a robot is trying to talk to you use using a bunch of beeping noise. A robot that communicates using FM is changing the pitch of the beep (high pitch or low pitch) to convey information. A robot that communicates using AM is changing the loudness of the beep.
FM is more popular because it has more bandwidth allocated to it – meaning more information can be transmitted to your radio. You can make AM sound better by using a larger bandwidth.
You want to talk to your friend who lives on the other side of a big lake or pond, it’s so big you can’t see him, but fortunately you can control the pattern of the waves and he can read the pattern (convenient!).
So, you and him have two ways to talk.
One. Amplitude modulation. You can send a 2ft wave, then a 5ft wave, then a 3 ft wave and so on, so that he receives the message 253.
Two. Frequency modulation. You send a bunch of 2ft waves, but send them at a varying frequency. So ___2_2___2___. He measures the frequency that the 2ft waves arrive and reads 3133.
The advantage of frequency modulation is that you can send more frequent waves than you can if you have to control the height of each wave.
Amplification modulation and frequency modulation are AM and FM.
You can turn a radio wave on and off to represent 1 and 0, but that’s slow with noisy data. What if, instead, you kept it on and ‘pulsed’ the wave? You could change either the frequency or the amplitude of the wave very slightly for a very short period of time. The faster you can ‘pulse’ info onto this wave, the faster you can send data.
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