Radio Fundamentals

Radio waves are simply a form of electromagnetic radiation, like sunlight, X-rays, cosmic rays, or infrared waves. The difference is that each has a different frequency and therefore different characteristics.

All electromagnetic radiation travels in straight lines at the speed of light. Earth is now surrounded by a sphere of radio and TV signals about 80 light years in diameter and expanding at warp speed. Because we on earth began radio broadcasting about 80 years ago. Something out there is listening to us. Real science fiction.

Interesting thing about radio waves in the .10 to 30 megaHertz(mHz) range. Often, instead of zooming off into space, they are reflected back to earth by layers of ionized particles in our atmosphere, 200 or so miles up. Appropriately these layers are called the ionisphere. This reflection process is often called "skip". The energy to ionize atoms in these layers comes from the sun. That is why you can hear the BBC London in North America or hear WLW Cincinnati, Ohio in California at night. Above 30 mHz radio communication is usually line of site. Radio signals at these frequencies and above are usually not reflected off of the ionosphere. Line of site means the distance to the horizon, about 30 miles from ground level in flat terrain such as Kansas. From the top of a 500 foot radio transmitting tower the horizon is a hundred or so miles away. This explains why you rarely get FM or TV reception beyond 100 miles away, unless you have cable, or unlesss there are some exceptional radio propagation conditions, such as sporadic E skip.

The range or spectrum of radio waves used for communication has been divided into arbitrary units for identification. Here are the divisions, along with a very few samples of what radio services you will find in each division. In the SW(Shortwave) division, where all the good stuff is, there are many more ham and broadcast band allocations, as well as many other radio services.

MW(medium wave) is the name given to the AM broadcast band, while VHF(very high frequency) and UHF may be familiar to those who watched TV in the pre-cable days. TV channels 2 to 13 were VHF and channels 14 to 83 were considered UHF. On air TV channels now stop at channel 70, the Federal Communications Commission(FCC) took away channels 71 to 83 years ago and reassigned them to the burgeoning cellular telephone industry. I have often wondered why in the United States there is no TV channel number 1. Most European nations have a channel 1 on their televisions. AC6V e-mailed me the answer to this perplexing question. There was a TV channel 1(44-50 mHz) in the United States until May 1948 when the FCC reassigned these frequencies to nongovernmental fixed and mobile services. Although this 44-50 mHz range of frequencies was mostly used by US FM broadcasters up until 1948. The FCC then gave these FM broadcasters until the end of 1948 to move to their current band of frequencies, 88-108 mHz, where they are today. The current US TV channel/frequency assignments are soon to undergo drastic changes with the advent of high definition TV(HDTV). This shift from analog to digital TV transmission will be gradually phased in, until all US TV stations will be broadcasting digitally by the year 2006.

Sunspot cycles

There is a phenomenon known as the sunspot cycle that also affects radio reception, also called radio propagation. Our local star, the sun, goes through 11 year cycles, at the peak of which there is a marked increase in the number of sunspots seen on the sun's surface. Explosions of solar energy erupt from these sunspots, travel to earth on the solar wind, and energize the earth's atmosphere. This is the same thing as the ionization I mentioned earlier. Long distance radio reception is often stronger and more reliable at the height of these 11 year cycles, although sometimes the solar energy becomes too intense. It can disrupt radio communications, interfere with electric power distribution networks, even getting into telephone wires and interrupting telephone conversations. At these sunspot peaks, displays of the Northern and Southern Lights are more intense and widespread. The minimum of the last solar cycle occured in mid-to-late 1996. The current cycle, cycle 23, is just now beginning, and will peak in the year 2000. Shortwave radio reception conditions should gradually improve from now until 2000. NASA, the National Aeronautics and Space Administration predicts that over the next ten years there will be a decrease in sunspot activity as well as in magnetic storms, cosmic rays, and ionosphere disturbances. Such a mild forcast could signal cooler weather on earth and less interference with radio communication. Cosmic rays have been known to cause problems in the sophisticated electronic systems of satellites.

UTC- Universal Coordinated Time

Formerly called GMT- Greenwich Mean Time. Since shortwave broadcasts often travel great distances and can cross many of the earth's 24 time zones, there is a need to have a standard time reference. UTC was developed to fill this need. It is based on the zero latitude which goes through Greenwich, England. Local midnight in Greenwich is 0000 hours UTC, while in the Ohio 0000 hours UTC is 7:00 pm local time, since Ohio is 5 time zones from Greenwich. Therefore a shortwave broadcast station can declare that its broadcast will begin, say at 1930 hours UTC, and listeners all over the world will know when to listen. Just by converting the UTC into their own local time.

Fading and Echos

An odd phenomenon I have noticed occasionally on shortwave stations. Listening to a station, say in California, from here in the Midwest, I have heard a slight echo on the voice. The signal from the California radio transmitter was coming into my receiver via two different paths. One was direct from California. The other signal came all the way around the earth, no problem for a shortwave signal, and entered my receiver from the opposite direction. The around-the-world signal, even traveling at the speed of light, took milliseconds longer to reach me, and when the two signals combined in my receiver they were slightly out of phase. I heard an echo. Weird.

Listening to an AM or shortwave radio, especially at night, you will notice a similar phenomenon. Fading. Again the radio waves reach your receiver two different ways. One signal hugs the earth's surface in almost a straight line, while the other signal bounces off the ionized layer and takes a bit longer. When the two signals arrive sufficiently out of phase, they tend to cancel each other out and the radio station seems to fade out in your receiver.

Gray Line DXing

Reception of medium wave and lower frequency shortwave signals is often best when the path traveled by the radio waves is entirely in darkness. This is true of my favorite shortwave broadcast band, 60 meters, centered around 5 mHz. There are many fascinating local African stations found here, great DX catches. There are two windows of opportunity to hear these stations, dependent on when a darkness path exists between Africa and North America. The first chance is around 6pm(2300UTC) Ohio time when it is midnight in West Africa. Many of these African stations sign off for the day at their midnight, allowing you to identify the station even if you don't speak French.The second chance comes about 1am(0600UTC) Ohio time which is just before sunrise in West Africa, when several of the African stations are signing on to begin their broadcast day. These same African stations begin to fade out an hour later as their sun rises. Is this cool or what?

Frequency and Wavelength

A potentially confusing subject encountered by beginning shortwave listeners is the relationship between a radio station's frequency and its wavelength. Early in radio's history radio stations were identified by their wavelength. Today frequency is the common way to locate a station on the radio dial. Although you will still find that a range or band of frequencies referred to by a wavelength number. For example the 19 meter(wavelength) band contains frequencies from about 15050 kHz to 15650 kHz. Best to keep a list of which bands relate to which frequencies, some shortwave receivers list the bands/frequencies used by international shortwave broadcasters right on the front of the receiver. By the way the mathmetical relationship is: frequency equals 300 divided by the wavelength.

Top of this page Top of homepage