Ham Radio

Radio waves can carry information around the world - including your voice, or a morse code signal, or a computer transmission. Thing is, you need a license from the FCC to legally transmit on the air, similar to how you need a driver's license to drive a car on the roads and highways. There's a somewhat technical test and a $35 fee for a ten year license, but it's very doable. Radios are relatively cheap and extremely capable these days, so in some ways there's never been a better time. Whether you're interested in radio wave propagation and antenna design, or making lots of contacts around the world, or getting involved in emergency communications, or radioing from parks and mountaintops, there are lots of interesting corners to explore.

How do you measure waves?

If you went to the beach and watched the waves coming in, you could use a tape measure to see how far it is from the top of one wave to the top of the next - that would be the wavelength. Or you could use a stopwatch to count how many waves arrive at the shore every minute and that would be the frequency. These two are related - if one goes up the other has to go down. For example, if you were standing at the beach and all of a sudden the waves started coming in much more often, then the tops of the waves would be much closer together.

All EM waves travel at the speed of light = c = 300,000,000 m/s or 186,000 mph. When you multiply the frequency (f) and the wavelength (λ), you get the forward speed of the waves. The formula is c = f λ

In practice, when you transmit on a radio, you set the frequency that you want to use, and that automatically determines the length of the wave that you are sending out. For example, if I transmit on 28.4 MHz then I am sending out 28,400,000 waves per second, and the length of each wave would be λ = c/f = 300,000,000 m/s  ÷  28,400,000 cycles/s = 10.56 meters long. We would say that's in the "10 meter band".

What's a "Band"?

Your car radio recieves two different sets of radio waves. One set of waves is the AM band, made up of everything between 530,000 Hz (waves per second) and 1,700,000 Hz. These waves all have wavelengths of hundreds of meters, travel in the same way and have similar "propagation".  Meanwhile all the waves in the FM band are between 88,000,000 Hz and 108,000,000 Hz, and have wave lengths about three meters long, and they all behave the same, but very different than the AM band.

In the same way, amateur radio frequencies are broken up into sets that behave the same, and these are called bands. Here's a partial list:

• 160 m band - 1.8 to 2 MHz - similar to AM commercial radio, good for local communication during the day and 100s or thousands of miles at night, lots of static during the summer

• 80 m band - 3.5 to 4 MHz - similar to 160m, but longer distances and often used for long conversations referred to as "rag chews"

• 60 m band - 5.332, 5.348, 5.3585, 5.373 & 5.405 MHz - a set of five specific frequencies that are shared with government agencies, and that come with certain restrictions

• 40 m band - 7 to 7.3 MHz - 

• 30 m band - 10.100 to 10.150 MHz - this band is only for data transmissions and morse code, but no voice. Your computer talks to your radio, which talks to another radio, which talks to another computer.   

• 20 m band - 

• 10 m band - 

• 2 m  band - 

• 70 cm band - 

Furthermore those, bands shaded in yellow are considered HF or "high frequency", while those shaded in blue are UHF/VHF or "ultra high frequency"/"very high frequency". Generally speaking, if you want to talk to someone in your town you would use UHF/VHF and if you want to speak to someone several states or countries away you would use HF.  

What frequencies can I use?

The FCC has allotted small slices of the radio wave spectrum to be used by ham radio operators, and these are shown in the chart below. Both the frequencies and wavelengths are shown, divided up into "bands". Additionally the chart shows where you can talk (called "phone"), send Morse code (called "CW" for continuous wave), or use a computer to send digital transmissions (RTTY, data, digital)

There are three increasing levels of ham radio licenses, each with increasing privileges to operate using more frequencies. These levels are:

• Technician (T) - talk/phone or send digital data on 10m, 6m, 2m, and 70 cm, 33cm, 23 cm AND can CW on 80m, 40m, 15m. (Just look for the "T" on each band) 

• General (G) - many more bands, more privileges

• Extra (E) - even more

• Note: the Novice (N) & Advanced (A) are leftovers from the old system of licensing and are still recognized but no longer being awarded.

The chart also shows how much power your radio is allowed to transmit. The max is generally 1500 Watts, unless otherwise indicated. However most hams are running something closer to 100W, and some like to use extremely low power "QRP" radios using only 5W or less. The second chart is another way to look at showing increasing privileges of the different licenses.

What's an antenna anyway?

To send and receive radio waves, your radio needs an antenna. It needs to be electrically conductive to carry the signal, and needs to be a certain length to tune in the signal, and needs to match your radio so that there aren't large energy losses that get converted into heat and could damage your equipment.

Similar to how the length of a guitar string determines the frequency played, the length of an antena determines the frequency (or wavelength) of the radio waves you are using. Often 1/2  wavelength of wire is common, and you can calculate the length of the wire by using the formula Length(ft) = 468/f or Length(m) = 150/f.

Here are some basics on the main forms of wire antenna

• Dipole - a halfwave of wire, cut and fed in the middle by a length of coax. Only works for one band.

• Doublet - a halfwave of wire, cut and fed in the middle by "ladder line" (parallel wires seperated by insulating plastic. Works for the band its cut for and all it's harmonics (other bands that are multiples of original frequency. Example: 14 MHz is the 20m band, and 2x14 MHz = 28 MHz, which is the 10m band)

• End Fed Half Wave - a halfwave of wire, fed at the end. Works for the band its cut for and all it's harmonics.

• "Random" Wire - a length of wire, that is not resonant at any frequency. Some lengths that work well are 29', 35.5', 41', 58', 71', 84', 107', 119', 148', 203', 347', 407', 423'  

• Vertical - a wire or rod that sticks straight up, like a car antenna.