Explaining Frequency and Wavelength to a Braille Reader

Recently, I had to explain frequency and wavelength to a group of blind hams. I remembered something from my childhood which I thought might help, and wanted to write it down. This will only make sense to braille readers.

“Braille is beautiful.” as we like to say, and I would suggest that every blind person learn it if possible. I did this using a piece of braille paper and a good old Perkins brailler. You can adapt it for a braille display.

In radio, we often talk about frequency and wavelength. Consider a stringed instrument, such as a piano, violin, or guitar. Lower notes have longer strings, and higher notes have shorter strings. This happens because of the wavelength. Lower frequencies have a longer wavelength, and higher frequencies have a shorter wavelength.

The same principle holds true for radio. However, instead of vibrating a string to produce audio waves, we send electromagnetic waves through an antenna. Lower frequencies require longer antennas, and higher frequencies require shorter antennas. This explains why you can get on VHF and UHF (2 meters and 70 centimeters) with a short rubber duck, but HF uses much longer antennas. My off center fed dipole has a length of 122 ft, and goes down to 80 meters. 3.5 MHz.

The names of the bands we use come from the wavelengths. For example, if we say that we will go on 40 meters, that means that the radio wave has a length of around 40 meters, or around 7 MHz. If we say that we will go on a repeater on 2 meters, that means that the radio wave has a length of 2 meters, or around 150 MHz. We will get into the formula to compute this further down.

For all of this to make sense, it helps to know what a radio wave looks like. Make a line of braille with “ieieieieieieieieieie” alternating across the whole line. This makes what we call a saw tooth wave, because it has a jagged up and down pattern. It has peaks and valleys. For a pure sine wave, like what you might hear when listening to CW (Morse Code), imagine the peak as the top half of a circle, and the valley as the bottom half of a circle. The wavelength refers to the distance between two of the peaks. On 40 meters, around 7 MHz, the wave has peaks 40 meters apart. Higher up, on 2 meters, around 150 MHz, the peaks have a distance of 2 meters.

Keep in mind that the wave moves through space. Imagine yourself standing at a point, watching the wave go past. A longer wavelength means that fewer peaks will go by in a second. A shorter wavelength means that more peaks Will go by in a second.

Actually, the frequency refers to the number of cycles per second the wave makes. It starts at the baseline, goes up, comes down, dips below the baseline, then returns to it. This completes one cycle. Old ham radio books don’t talk about Hz (Hertz), they talk about cycles per second. You may even hear old timers referring to a net on 80 meters as 3.5 megacycles. This means that the wave goes up and down 3.5 million times per second.

This also explains why we talk about using upper sideband (USB) or lower sideband (LSB). It refers to which half of the wave we use. Upper sideband uses the part of the wave above the baseline, and lower sideband uses the part below the baseline. If you tune into the wrong sideband it sounds garbled.

When we say a radio wave, we really mean an electromagnetic wave. You could think of light waves as like radio waves at a much higher frequency. Electromagnetic waves travel at the speed of light, around 300,000,000 meters per second, or 300 megameters. That explains why if you divide 300 by the frequency in megahertz you get the wavelength in meters, and if you divide 300 by the wavelength in meters you get the frequency in megahertz. This works approximately. The 2 meter band, which before I described as around 150 MHz, really goes from 144-148 MHz, but that comes down to rules we invented.

I hope this helps some blind hams. 73, and keep hamming!