I’ve recently started studying Ham Radio, and I found that even the Ham Radio For Dummies book didn’t make it very easy for me to visualize wavelength. Since they made me puzzle out how to visualize wavelength, I thought I would post my own guide with pictures. I’ve tossed in frequency as well, since that’s helpful to the discussion.
Experienced hams, please feel free to chip in with comments if anything I’m writing is misleading or inaccurate, or if there’s something I could add to make it better!
Radio signals don’t travel in a straight line. Instead, they vibrate up and down really fast. It would look something like this if you drew it out on paper. (All my illustrations will be hand drawn in this tutorial.)
Grab a real (or imaginary) 3×5 note card and follow along with me. First I’m going to make two radio waves. Each will travel the same amount of distance (from one end of the note card to the other), but as you can see, they look really different:
The thing that makes these two radio waves different is frequency. The top one is low frequency, because it only made a couple repeats of its pattern before running out of room. The bottom one is higher frequency — it got through a bunch of pattern repeats.
The name for one single repeat of a pattern is “cycle,” as in, “Wow, that only made it through a few cycles before hitting the end of the note card.”
Cycles don’t have to be the same distance for two different waves, as you can see here. This cycle below is obviously much shorter in distance than the one above, even though the two waves are both drawn out on the same length of card.
Basically, we need a way to compare one cycle against another easily, without having to draw everything out each time. That’s where frequency comes in.
If you look at the wave I drew out above, the distance that I marked out for one cycle also could have a time stamp attached to it. In fact, that’s how you usually measure a cycle — in time.
For example, perhaps the big fat cycle on the card below took 1 second for each cycle to happen, but the little one beneath it only took one third of a second per cycle (after all, there are about 3 skinny waves for every single fat one in this picture).
This is assuming the two waves are on the same time base. In other words, it takes the same amount of time to reach the far side of the note card no matter what the wave itself is doing. (This isn’t always a safe assumption, but we’ll assume so for just this one example.)
So that’s frequency — basically just how many times one given thing happens in a given period of time.
Frequency is usually measured in “Hz,” or hertz, to spell it out. Hertz is the technical term for how many times something happens in exactly one second. By sticking to “number of times in one second” all across the board, it gives an easy method for comparing one thing to another.
If the number of hertz is really big or really small, it may also have a prefix — like megahertz, which means one million hertz. So, if you have 5 megahertz, that means something is happening five million times per second.
Ok, here’s where we get to wavelength. Radio waves only come in one speed: the speed of light, which is always the same everywhere. Because of this, wavelength is a little easier to figure out.
When I drew out these cards, it took me a certain amount of time to draw each full length wavy pattern. And it wasn’t the same amount of time for each one, even though I was covering the same horizontal distance for each waveform — from one side of the note card to the other.
However, my drawing speed was pretty constant, whether I was drawing a high frequency wave or a short frequency wave. So, in this case, my drawing speed will stand in for the speed of light, which is also constant.
Quick, which wave do you think took longer for me to draw, even though I was drawing at the same speed for each?
If you said the one on the bottom, you’re right. How long did it take? I’d say about 3 times longer than the one above. So, it took that wave about three times as long to “travel” the same distance as the one above it (they both traveled the length of the 3×5 note card, but the lower one took longer and used more ink).
So, how far along the note card did my lower wave travel in its first cycle? Maybe 1/2 inch at most. But the upper one traveled way further in its first cycle — about 1 1/2 inches of travel in the same drawing time as the lower waveform. It’s just that the lower cycle is squished together and the upper one is lazily spread out horizontally.
That’s wavelength: how far does a radio wave travel (in physical distance) in the time it takes it to complete one cycle of its wave pattern.
The application of all this?
Well, if you increase the frequency/hertz of your radio wave, the result will be that its speed of travel will go down, and its wavelength will be shorter. In other words, the higher the frequency, the more your radio wave acts like a dog on a hike, running back and forth sniffing things instead of putting all the effort into moving forward on the trail. Remember, the speed of light is fixed, so any energy put into detours means the wave takes longer to get where its going.
On the other hand, if you make your frequency/hertz lower, the result will be that its speed of travel will go up, and of course, the wavelength will be longer. (Less running around, more moving forward toward its destination.)
So that’s basic frequency and wavelength.
Note: Since writing this post, I’ve started using hamstudy.org to study for my first ham radio exam. I would highly recommend it for anyone who wants to get their license! I found it through this excellent blog post: How To Get Your HAM Radio License In 7 Days.