(This is a somewhat updated version of an article I first wrote on my old static website back in 2006).
Actually, the term as its used in North America is a bit of a misnomer. “AM” refers to the type of modulation used to transmit the signal (amplitude modulation).
The more accurate term used in most other parts of the world is the “medium wave band” which refers to the part of the radio spectrum between 530 and 1700 KHz. (kilohertz). Medium wave hobbyists will tend to use the term “AM broadcast band”.
In Europe and North Africa, there is actually a “second” AM broadcast band known as the “longwave” band that runs roughly between 150 and 300 KHz.
Most radio stations that broadcast on the international shortwave bands also make use of “amplitude modulation”.
Be that as it may, “AM radio” has gotten a bit of a bad rap over the last couple of decades. People often complain of the poor audio quality of “AM radio” and the problems with “static”.
Actually, there are many techological “fixes” that can indeed improve the audio quality of AM radio. The problem for the most part has been in the implementation. The electronics industry, broadcasters and government regulators have been involved in endless disputes over the establishment of standards that could impove audio quality. These disputes date back to the 1980’s with disputes over standards for “AM stereo”.
In recent years, some of the radio broadcasting industry has been working on “DRM”…no, not the evil “digital restrictions management” that we know from the world of digital media, but rather “Digital Radio Mondiale“. If everything falls into place, the radio stations adopt the standard and the receiver manufacturers start making the radios we could end up listening to beautiful digital audio not only on the medium wave band, but also on the long and shortwave bands!
Mind you, given the history of the industry, that’s a big “if”.
As for the “static” heard on the AM broadcast band, most of it isn’t static at all. Sure in summer when there are summer thunderstorms around you will often hear static electricity on your AM radio.
Static is a “natural” phenomenon, while the other kinds of noises you hear are not…they’re created by human activities and endeavors. Poorly maintained power lines, fluorescent light fixtures (including the “compact fluorescent bulbs), computer equipment, poorly designed electronic products and if you’re in Toronto, the TTC’s current fleet of streetcars all generate “RFI” or “radio frequency interference” that disrupts your ability to listen to AM radio.
That’s why you’ll get the best mediumwave reception out in the country where you can away from all of these “human-generated” sources of noise. Ham radio operators have two “short forms” that differentiate between radio interference of the “natural” kind and that caused by homo sapiens.
“QRN” refers to static crashes caused by thunderstorms, while “QRM” refers to interference caused by our various electrical and electronic devices.
The one really interesting property of the mediumwave broadcast band is the ability of signals to travel relatively long distances, particularly after dark.
During the daytime, signals on the mediumwave band will travel for not much more than a few hundred kilometers depending on the output power of the transmitter. After dark, signals on the mediumwave band can easily travel a couple of thousand kilometers and in exceptional circumstances travel for many thousands of kilometers. That’s because the “D layer” of the ionosphere allows radio signals to literally bounce off of it!
During “auroral” conditions, when solar storms are quite active signals from “mid-latitude” stations will be attenuated somewhat permitting signals from points further south to be heard. For instance its not uncommon to hear stations from Colombia and Venezuela here in southern Ontario during auroral conditions.
In very exceptional circumstances its possible to hear mediumwave radio signals from Europe. This usually happens at the “low” end of the eleven year sunspot cycle To do this however, you will usually need a good quality receiver, good outdoor antennas, an electrically quiet location, the “right” solar conditions and some good luck.
Many of us as youngsters got into “twiddling the dials” of our radios at night to see what we could pick up. There’s actually a radio “sub-hobby” called “AM Broadcast Band DXing” or “Mediumwave DXing” depending on “what side of the pond” you’re on.
AM Broadcast Band “DX’ers” will twiddle the dials of their radio equipment to try to see what they can pick up at night.
And a “sub” sub hobby that’s developed in recent years amongst some particularly fanatical AM Broadcast Band DX’ers has been “ultralight” DXing!.
What’s that you might ask? It’s a hobby of trying to pick up exotic long distance AM radio stations using usually very inexpensive and very small radios.
The radio that launched this hobby is a little “Walkman style” AM/FM radio made by Sony and is their model SRF-59. It has no built in speaker (you listen using headphones or an external speaker) and it runs on a single AA battery! They cost about $20-30 here in Canada.
Just by luck, I found a set of matching speakers for my Sony SRF-59 in a department store in of all places Barcelona, Spain.
Here’s a Youtube video of someone in Northern Ireland using an SRF-59 to tune in Toronto’s CFRB 1010 at his local dawn using one of these little radios!
Here are some website links that you may find of help. Even if you don’t care about picking up exotic signals on your AM radio, information on the sites will help you with your every day AM radio listening!
National Radio Club
International Radio Club of America (IRCA)
“Bamlog” (Bruce’s AM Log)
Wikipedia article on Medium Wave DXing
YLE (Finnish Television) video on Mediumwave DXing (Real Media format)
Radio Locator – An online searchable database of radio stations
DX World.com Broadcast Band Propagation Logger – You can report what stations you’re hearing on the AM broadcast band in “real time”.
The AM STEREO Page – Information on AM stereo and AM stereo receivers
AM Stereo.com – Another AM stereo site
“DX Tools” Small company specializing in accessories for MW/LW radio listeners.
WA1ION’s RF Circuit Design Page – A wealth of information for “do it yourselfers!”
Radio JayAllen.com – Article on combatting interference to AM radio