AM 890 Homer AlaskaAM Radio Interference: Causes and solutions
AM radio offers challenges for good reception. It is susceptible to various kinds of interference, both natural and man-made. And sometimes it's hard to find a radio that gives you decent AM reception.
Let's take a look at the first truth of AM reception - a good antenna. Outside of a few select radios engineered with AM radio listeners in mind, most radios treat AM radio like an afterthought. Many radio manufacturers have relegated AM radio to the past - to the days before FM - and they aren't fully aware of AM's continued popularity across the country. The consequence of this move away from AM is that many radios just don't have very good AM antennas.
AM reception can vary a great deal from day to night because of differences in the atmosphere. You may get good, clear reception during the day, but after sunset the signal may fade or become distorted. Signals travel further at night, so you may get interference from other transmitters a considerable distance away.
One fairly common source of AM interference is dirty or faulty insulators on nearby electrical utility poles. This can be an issue on the Kenai Peninsula following volcanic ash fall, such as we experienced in April 2009 with the eruption of Mount Redoubt. Though summer rains may wash much of the ash away, enough may linger on the insulators to be a continuing problem.
The Antenna is 90% of Your Radio
Who ever thinks about the antenna for AM? Yes, for FM you have the rod antenna that you pull up and move around, or that piece of wire that came with your stereo that most people leave dangling in a tangle behind the entertainment center (then wonder why their FM reception is no good...). A good AM antenna is of the essence: an inexpensive radio with a good antenna will outperform an expensive radio with a poor antenna. A good antenna where there's no signal won't make a difference: the antenna has to be in the path of the radio signal.
Your AM radio has an antenna, too. In most portables, transistor radios, boom boxes and table radios, the AM antenna is built in. It consists of a ferrite rod around which is wound thin wire. Since we don't see this antenna, we tend not to think about it, but it's there nevertheless.
This antenna is directional-- that is it picks up signals from some directions better than others. This built-in antenna is best at picking up stations coming in from a direction perpendicular to the rod. It is least sensitive picking up signals coming at it end-on. This phenomenon can be used to your advantage. To get a station in better, try turning the radio. By doing so, you are aiming the antenna inside for a better signal. And if there is interference, you may be able to get the antenna rod pointed end-on toward the interference, thereby reducing it or cutting it out completely.
What if you have a nice stereo system, with a receiver or a rack system? In those cases, the AM antenna is often a loop of wire wrapped around a small plastic frame that you connect to AM antenna terminals on the back of the stereo. If you don’t have the antenna that came with your tuner, get a length of wire, maybe 20 feet or so, and wrap it around something non-metallic to make your own loop. You might try using a cheap plastic food dish, for example. Wind the wire around its circumference, then strip the ends of the wires and connect them to the AM antenna terminals. As with the ferrite rod described above, it is directional, so experiment with the correct placement.
Many older stereo tuners and receivers had the ferrite rod antenna mounted to the back of the cabinet on a hinge. Again, experiment with aiming it for the best results
Tips for Improving Your Reception Quality
Reception works better near windows. Avoid areas covered by metal, brick, or concrete. There is an exception to this rule. If there is a source of interference you may improve your reception by moving away from it. Moving away from a window that is close to a power line may improve your reception.
Properly orient your AM antenna. The telescoping antenna that sticks out of your radio is for FM, not AM. The AM antenna on a portable radio is usually a ferrite rod with a thin wire wound around it. The AM antenna is inside the radio and normally runs across the back of the radio parallel to the ground. To get the most signal either the front or back of the radio should face the broadcast tower so the antenna is perpendicular to the signal, like a sail spread out to catch the wind.
If your radio has controls for treble and bass then turn the treble all the way down and the bass up. If you have a control for tone only then turn it all the way down. Many inexpensive radios do not have these controls, but if your radio does have these controls this is a cheap, easy solution that can eliminate much of the static.
To minimize interference from a known source, point one end of the antenna rod at the source of interference. As the antenna rod normally runs along the back of the radio, parallel to the ground, you point either end of the radio at the source of interference.
Sources of Interference
AM radio is susceptible to natural and man-made interference due to the way the signal is carried over the air and demodulated (or "decoded") in your radio. When you are looking for interference it helps to know what the likely sources of interference are. Unfortunately there are many sources of interference. The lucky thing is that the interference often disappears if the radio is not within a foot or two of the interference. Often, but not always. The following things can cause interference on your AM radio:
Identifying the source of interference
An obstruction between you and the transmitter, such as a mountain or tall buildings sometimes blocks the signal.
Wood-frame buildings with wood siding shouldn't cause much of a problem. Brick, cement block, stucco, aluminum, or metal-sided buildings almost always cause AM reception problems unless you have a lot of windows, which do not usually block AM radio waves.
Sometimes people can't get any AM reception in certain places, such as their workplace. The building may be made of metal, use reinforced concrete walls (metal rods in the concrete to strengthen them) or have a metal roof. There may be computers or machines that cause interference, and numerous florescent lights in the ceiling.
If you are not sure where the interference is coming from, get a battery-operated radio. If the interference disappears, then it was coming through the AC power line. RadioShack and other retailers of electrical parts and accessories sell AC Line Interference Filters that can reduce this kind of interference.
Using the battery-operated radio, turn off all circuit breakers to see if the noise stops. If it does then you know it is something in your house. Turn off one circuit at a time to isolate where it is coming from. You can also look for interference by turning individual appliances on or off.
If the interference does not go away, then it is coming through the air. If this is the case, use the battery operated radio as a "direction finder" to locate the interference. When you find the position where the interference is the loudest, the front and back of the radio will usually point to the noise origin. Walk around with it until you come to where the interference is strongest. If it turns out that the interference is strongest near a utility pole, call the electric company, and see if they'll come out to wash or repair the insulators on the pole. A transformer on a utility pole that is in need of repair can be another source of interference from outside your home.
Caution! Do not mess with electrical circuits or devices unless you are a qualified technician. Leave that to the professionals as it is dangerous.
Once you have identified the source of the interference, and if it is something you can control then you're all set.
Sometimes moving the radio to a different location, or even turning it (so the internal antenna is aimed in a different direction) may be enough to reduce or eliminate interference, yet still leave enough signal to listen to the station you want.
Note that interference is always a radio signal, whether it is a signal from another channel or a buzz from a florescent light. You can find buzz interference with a radio. If you have a portable radio you can move it around looking for the buzz. If you put the radio up close to a source of interference, for example, florescent lights, it should buzz loudly, the buzz will decrease as you move it away.
Also the buzzing will increase if the front, back, top or bottom of the radio faces the interference, and decrease if the left or right end of the radio faces the interference. This is because the interference decreases when either end of the ferrite rod antenna points at the interference, and increases when the length of the rod faces the interference.
This can help you to determine almost exactly
where the
interference is coming from. For example, play with the radio in
various places
in your home/office and find out at what angle the buzz disappears. Do
this
from several parts of the room and look for the intersection of several
straight lines. This can help you zero in on the interference source.
Interference sources you cannot simply turn off
Unfortunately, there are many other interference sources that cannot simply be turned off. Here are some of the more common ones with suggested solutions:
Touch lamps, the type you turn on by simply touching the base, have to be unplugged not just turned off.
Light dimmers can cause interference even if they are in your neighbor's apartment. If you have one in your home, you can have it replaced with a regular switch.
Hard wired smoke detectors cause interference, they can be replaced by battery-powered models.
Aquarium heaters, particularly some cheaper models, cause interference. You can upgrade to a better model. The key point is the way the thermostat turns the heater on and off. In cheap heaters the electricity can arch when the heater is about to turn on. In the more expensive models little magnets pull together and complete the circuit in a quick way that prevents arching.
Automatic on/off night-lights and outdoor yard lights that come on automatically also generate interference.
Dirty or faulty insulators on utility poles can cause interference, you can phone the utility company and ask to have them repaired or replaced.
A faulty electric switch in your house can cause interference. You can have it replaced. This might be a good idea even if you are not concerned with AM reception.
The interference may be coming through the electric socket that powers the radio. If the problem disappears when you use a battery-powered radio then you have found the source of the interference.
Some older radios have plugs that are not
polarized. If you
can flip the plug over then the plug is not polarized. Sometimes the
interference can be cut by turning the plug over and putting the prongs
in the
opposite socket holes.
Is another
station interfering with your reception?
David J. Charlton
FCC Enforcement Bureau
P.O. Box 221849
Anchorage, AK 99522-1849
Phone: (907) 271-6342
Fax: (907) 271-6359
24 Hour: (202) 418-1122