Frequency and wavelength are inversely related properties of electromagnetic waves, including radio waves used in amateur radio transmissions. In ham radio, understanding the relationship between frequency and wavelength is essential for effective radio operating.
Basic Relationship Between Frequency and Wavelength
The frequency of a radio wave is the number of cycles it completes per second, measured in hertz (Hz). Wavelength, on the other hand, is the physical length of one cycle, measured in meters. This formula mathematically relates these two parameters:
Where λ is the wavelength, c is the speed of light, and f is the frequency.
This is often simplified to λ = 300/f, with λ in units of meters and f in units of MHz. Because of the inverse relationship between frequency and wavelength, higher frequencies correspond to shorter wavelengths, and lower frequencies have longer wavelengths.
Ham radio operators can use different frequencies for various types of communication, often grouped into bands (e.g., the 80-meter band, the 40-meter band, or the 20-meter band). These band names refer to approximate wavelengths, which can help operators select the right frequency for a given distance and purpose.
Here's a chart of the most popular amateur bands in the high frequency (HF) spectrum:
Notice how the band or wavelength decreases in value as we move downward on the table. At the same time, the frequency is increasing.
Let's take a look at the 10-meter band. At the low end of the band (28 MHz), the wavelength is actually 300/28 = 10.7 meters, while the high end of the band (29.7 MHz) corresponds to 10.1 meters. So, we round the wavelength off and call it the 10-meter band. It is interesting to note that the wavelength for the 15-meter band goes from 300/21 = 14.3 meters to 300/21.45 = 13.9 meters. So maybe it should have been designated the 14-meter band? I dunno. You'll also find that the 20-meter band spans 21.4m to 20.9m. To make it slightly more confusing, the phone portion in the upper part of the 80-meter band is so short in wavelength that it is also called the 75-meter band. (300 / 4.0 = 75 meters)
Mixing It Up Can Cause Confusion
The terminology in ham radio can be confusing because we often refer to bands by their wavelength (like the "20-meter band") but also talk about specific frequencies within those bands in megahertz (MHz). For instance, the 20-meter band covers frequencies in the range of 14.000 to 14.350 MHz, so when someone says they are on "14.200 MHz," they designate a specific frequency within the 20-meter band.
We often switch back and forth between wavelength and frequency, which can be confusing for the new ham. With experience, you'll just know that 7 MHz is in the 40-meter band, but when you first start out, you'll probably want to refer to a band chart. Sometimes hams are a bit sloppy with their terminology. For example, someone might say, "There is excellent propagation on twenty tonight." Did they mean 20 meters or 20 MHz? For amateur radio purposes, they surely meant 20 meters because 20 MHz is not an authorized frequency. But what if I say I was working DX on 10? Does that mean 10 meters or 10 MHz? We have both.
GHz, MHz, kHz
If I want to schedule a contact with someone on 20 meters, I will probably specify a frequency, such as 14.250 MHz. Otherwise, it may take a while to tune around and find the other station. Most of the time, frequency in MHz works well for the amateur bands. You may also encounter frequencies specified in kHz, which means the decimal point moves three places to the right, compared to MHz. For example, 14.250 MHz equals 14250.0 kHz. For the shorter wavelengths (higher frequencies), we might use GHz, which is 1000 times a MHz. That is, 1296.0 MHz equals 1.296 GHz (move the decimal point 3 places to the left.)
When using kHz, a ham might say, "Meet you on 14250," assuming that you'll know it's the 20-meter ham band at 14250 kHz. Another shortcut happens when both hams know they are talking about the 20-meter band, and one of them says, "I am listening on 250," meaning 14250 kHz or 14.250 MHz.
Higher or Lower?
When teaching license classes, we've been known to say something like, "The higher HF bands work best during daylight hours," referring to the 20-, 17-, 15- & 10-meter bands. Sometimes, a student has a quizzical look on their face, wondering how the 10-meter band is "higher than" the 80-meter band. After all, 10 is smaller than 80. Of course, what's going on is that the instructor is thinking about the radio waves being higher in frequency, not wavelength. Again, wavelength is the reciprocal of frequency, so the numbers move in the opposite direction. It is probably better to express it this way: "The higher HF bands (greater than 14 MHz) work best during daylight hours."
What To Do?
First off, be aware of this potential confusion when flipping back and forth between frequency and wavelength. Frequency and wavelength are well entrenched in the hobby, so neither of them is likely to disappear. If you are talking to a new ham, be very specific with the frequency and indicate whether it is expressed in MHz, kHz or GHz. Reduce the ambiguity. Do the same thing with wavelength or band by explicitly saying "meters."
If you are the new ham, keep a band chart handy to aid in interpreting discussions that intermingle frequency and wavelength, and don't be shy about asking the question for clarity. With experience, it will become second nature to make the connection in your brain.