I was pretty bored and I decided to switch on my radio just to kill time, and it really did help me to annihilate and to murder boredom.
I was switching and tuning from one local FM station to another with sheer aplomb like I was flexing and cruising in a Ferrari and I even went further, in tuning to the AM bandwidth, where I listened to foreign radio stations like the BBC World Service and VOA etc. I was pretty much on top of the world and it felt like the whole world was in my hands … quite a number of radio stations were pleading and begging for me to select them.
Just like A-B-C, life was so easy while I was chilling, sipping some juice, with some shades on, tuning and switching stations on my radio device like I ran the world.
It was such an amazing feeling, flexing and doing all that and I’m not going to deny one thing. Also, it got me into real deep thoughts and I was pretty confused, curious, and also eager to know how the radio worked. Why FM sounded way better and why AM covered more area.
So please stay with me and don’t change the dial.
Basics
For you to listen to the radio, a couple of things must happen. First of all, modulation must occur, which is such that the radio station needs to encode some sort of information into a radio wave. After which the station needs to broadcast these radio waves on a particular frequency. The antenna of your radio picks up the broadcast based on the frequency your radio dial is turned to. Information from the radio wave is then decoded by the radio which plays the information via the speakers as sounds. Now, you must wonder where the information comes from.
AM and FM explained
When I say AM and FM, I'm sure you know I don't mean ante meridian and football manager respectively. AM means amplitude modulation, which implies that to encode information the amplitude (height of wave) of the radio signal is used. FM stands for frequency modulation. Here, a change in frequency (number of waves that passes per second) is used in encoding information. We can see that both use modulation in encoding. So what exactly is Modulation?
Modulation may be defined as the variation of some property of the radio carrier in a manner that conveys information.
Modulation debugged
To fully understand why modulation is important I will use the semaphore flag analogy. Stop looking at me that way. Semaphore is a way of conveying messages by holding two flags. Different positioning of the flags mean different letters or numbers. Now, If you are trying to convey a message and you hold the flags in the same position, the messages are the same. The person you are trying to relay the message to won't be able to understand the message as he will see no difference in meaning.
In semaphore, outstretching your arms would mean the letter “R”, while if you outstretch your right arm and place the left arm above your head you are representing the letter “P”.
With the analogy delivered, the concept of radio modulation should be easy to understand. If a simple sine wave is to be transmitted by a radio station, to encode the information wouldn't be possible as the message would always look the same. To send out any useful information, the radio station must find a way to manipulate the shape of the radio waves, which is done using either form of modulation. Let's start alphabetically.
AM - Amplitude Modulation
I'm sure you are still wondering how exactly the information is encoded. The first thing you need is the carrier signal (a simple unmodulated sine wave), a wave that has no change in amplitude or frequency. Next, you need a wave that resembles the information you want to pass out. The amplitude of the wave will change based on the message send out.
For the sake of simplicity, let's assume we want to send out letters instead of sounds, letter A will be represented by a small amplitude, while Z will be represented by a very big amplitude and other alphabet letters will fall respectively in between. You can think of it as a geometric progression or arithmetic sequence will a positive common ratio and common difference respectively.
Once both the carrier and the message signals are ready, we multiply them together. When this is done, the amplitude of the carrier signal is changed in accordance with the amplitude of the message signal. The actual broadcast signal consists of the combined waves of the carrier and message signals. When your radio antenna picks up the signal, the radio must then determine the difference between the amplitude of both signals and convert these differences in amplitudes back to letters.
In simple terms, if the difference between the amplitude of the waves is 2, that is equal to letter A, if the difference is 4 that's letter B, if the difference is 6 ... well you get the gist. That's simply how amplitude modulation works. Pretty easy, right? Now let's talk about the other form of modulation and learn how it is done and later in the post I will explain which is best and why.
FM - Frequency Modulation
If you understood the concept of AM modulation then you should have no problem understanding this since it's almost the same thing. Again you need a simple sine wave to be the carrier signal and you need to develop the message signal. Now, instead of varying the amplitudes as in AM modulation, you vary the frequency of the carrier signal.
In simple terms, the lowest frequency will represent A while the highest one will represent Z and others fall in accordingly. When your antenna picks up the final signal, the changes in frequency will be used in decoding the actual broadcast message.
Why FM radio stations sound better
If you are a radio enthusiast like myself, you must have noticed that the FM radio stations sound way better than the AM radio stations. Did you ever find out why? If not, then today is your lucky day. I will fill you in on the details why FM radio stations sounds better than the AM radio stations. The three main reasons responsible for this are: the signal strength, interference, and frequency range. Let's start with interference.
- Interference
The sun, yes that one up there produces a lot of AM radio waves and most radios are not able to distinguish between the natural AM waves and the ones broadcast by your favorite AM radio station. This is why your AM radio seems to sound better at night. This interference is one of the reasons why the FM radio stations sound more sonorous than the AM radio stations.
- Signal strength
Another reason for this is the signal strength at which these two forms of radio broadcast. The FM radio stations can transmit their broadcast at up to 100 kilowatts of power while AM radio stations can only broadcast not exceeding 50 kilowatts, this is due to national regulations like the Federal Communication Commission in the United States and the Nigerian Communications Commission in Nigeria.
Also, by altering the amplitude of broadcast signal for AM radio, the power at which the signal is transmitted is also affected, as the amplitude is the strength of the signal. Whereas in FM radio the amplitude doesn't change, therefore the strength of the signal doesn't change.
- Frequency range
Lastly, one other advantage the FM radio has over the AM radio is that it can broadcast over a higher frequency range. The FM stereo operates between 88 MHz and 108 Mhz with an increment every 200 kHz, while one the other hand, the AM radio operates between 535 kHz and 1605 kHz, and when you change the dial on the AM radio it's number changes by 10 kHz each time.
This means the stations have 10 kHz of bandwidth each to broadcast on. Although due to NCC and FCC regulations, FM stations can only use 150 kHz of bandwidth, it is still 15 times that of the AM stations. Simply put, the FM radio stations can transmit 15 times as much information as the AM radio stations can.
Why AM covers more area
With all I’ve said above you may be wondering why anyone still uses AM radio. But if you noticed earlier in my introduction I was curious as to why AM radio covers more area which is the only advantage it has over FM radio. Now, let me explain to you why it is so. I'm going to paint a scenario so you can understand.
Imagine you are traveling from Kano (north) to Ibadan (south west) by land, you will have to pass through several cities. So, let's say flooding occurred in one of the cities you are supposed to pass - let's assume Benin city (east) and you are not sure whether you will be able to pass through. It would do you well to know ahead of time so you can plan your route accordingly. Wouldn't it be nice if you could have a station broadcasting Benin city traffic reports while you are still in Kano? Is this even possible? The answer is yes, it's possible.
Since AM radio broadcasts at a lower frequency, it has a larger wavelength (frequency of a wave is indirectly proportional to its wavelength). Larger wavelengths are able to travel farther as they can travel through solid matter. FM radio, however, has shorter wavelengths and doesn't travel well through solid objects.
To paint a clearer picture, a girl can run in the rain, but a mosquito can't since it's almost the same size with a raindrop. The wavelength of AM radio is are much bigger than the atoms of the solids that's why they can easily travel through them (just like the girl in the rain). FM wavelengths are smaller when compared with the atoms of solids. Therefore can't travel easily through it (just like a mosquito can't fly in the rain).
AM radio waves are also reflected off the ionosphere which is another reason why we can hear them from far away. Lower frequency waves are easily reflected than high frequency waves.
Conclusion
I personally enjoy listening to radio, it's liberating unlike the television that I always have to look at the screen. I can keep radio in my pocket and listen to it as I walk around in hot sun. It will be a cold day in hell the day I stop listening to radio.
Although, over the past decades, the usage rate of radio has dropped significantly due to advancements in technology. Radio used to be a lifesaver, my dad told me he listened to the whole of the 1978 World Cup on the radio.
Now that you have understood the that radio reception depends on some many factors ranging from geological location to type of modulation, I guess you now know why you can't find your favorite AM station at a particular time of the day or why you can't listen to your beloved FM station when you are out of town.
References
J.J Carr. “Elements of Electronic Communications.” Reston, Virginia: Reston Publishing Company, Inc., 1978.
R.S. Carson. “Radio Communications Concepts: Analog.” New York: John Wiley & Sons, 1990.
Editors and Engineers The "Radio" Handbook. Los Angeles: Editors and Engineers, 1942.
AM vs FM; differences and comparison
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