Radio Station Interference
What in my home would make an AM radio whistle on
some stations? A computer? I have a nice 20 year old AM/FM table
radio that has this problem. I took it to a service company and
when they plugged it in there was no problem. They could offer no
Sometimes AM radios will have a whistle if they are placed too close
to a TV or computer monitor. FM should not be affected by this. If
the AM stations sounds good somewhere else in the house then it
probably is too close to the TV or computer monitor.
Any electromagnetic radiation from external sources (such as a microwave,
computer, mobile phone, nearby tv station, etc.) can cause the
noise. Many other electrical devices such as motors (as in washer/dryer,
fans, heating/cooling units, furnace fan, attic fan, refrigerator),
specially when placed close to the radio, can cause the noise.
Essentially, your radio receives the waves (radiation) sent out by radio
stations. When you tune it to a particular wavelength, you hear the radio
station that broadcasts on that wavelength. You do not hear other stations
because they broadcast at other wavelengths.
Microwave stoves and other emitting devices also produce electromagnetic
radiation. Another source of radiation could be faulty electrical wiring
inside or outside the house. An electrical appliance that is defective can
also cause noise. The radiation can have a broad bandwidth causing noise
across a large section of the spectrum (i.e., on many radio stations). In
the US, FCC, the Federal Communication Commission, regulates the radiation
power (noise level) that electronic devices may produce. This is to
prevent what is called interference (indicated by ghostly tv images, noise
on the radio, etc.).
Regarding your radio, I suggest the following:
Borrow a radio that operates both on battery and on 120 V
electricity. Plug both radios into the wall outlet. Here are the
1) If both radios are noisy: there is external noise in your area or on
your supply line. Operate the borrowed radio on battery. If it is noisy
too, then you have external noise. Cut off the power supply to the house
at the main. If the noise in the battery-operated radio goes away, then
the source of the noise is an electric unit inside the house. If the noise
does not go away, there is external noise and you need to check with your
electric/phone/cable (?)company or seek the source in your neighborhood.
2) If the borrowed radio running on wall electricity is not noisy but your
radio is, then your radio need repair.
Dr. Ali Khounsary
Advanced Photon Source
Argonne National Laboratory
Argonne, IL 60439
It is quite possible that a nearby computer or other electronic appliance is
causing this whistling. Try a portable radio in the same area and see if
the same problem. If it does, try walking around the room to localize the
problem (or try pointing the antenna to different parts of the room. It
should be quietest when the antenna is pointing directly at (or directly away
from) the source of the noise.
Once you think you have located the noise source, try turning it off (and
unplugging it if it has circuits that remain active when turned off).
The radio located in the residence that has a "whistle" or possibly a heterodyne, may be near another AM radio that could be
tuned to a different radio station.
AM radios (assuming the question is about an AM radio) emit radio signals that change frequency as the radio is tuned.
When AM radio one is close enough to AM radio two to receive the signal transmitted by AM radio two (or vice versa) and
the frequency offset of the two radios is correct, then AM radio one will have a heterodyne or "whistle"
This is caused by the signal from AM radio two beating against the broadcast signal AM radio one is tuned to.
To demonstrate this, you will need two AM radios. Tune AM radio one to a radio station in the middle of the AM
broadcast band. While close to each other, start tuning AM radio two from the bottom of the AM band moving up to the top.
At some point on the dial of AM radio two, you should start hearing a whistle on AM radio one. This is the heterodyne caused
by the very low level signal emitted by all AM radios.
I discovered this interesting fact when in the Army and while living in the old open bay barracks. There were 3 soldiers that
would play their favorite AM stations without consideration of others that were listening quietly to their radio's or music. If you
asked them to turn the volume down, they would turn the volume up instead.
While tuning through the AM band one day, I tuned through the correct frequency and found that my radio would interfere with
the radios that were turned up too loud. As the owner of the radios with the heterodyne could not tune it out, the radios were
turned off quickly.
No one ever discovered that my radio was the source of my newly found AM broadcast jammer.
This was ironic in a way. Two of the men that liked to turn the volume up, were being trained to jam communications systems
with radio transmitters that could jam AM, FM, and Television broadcast station as part of their electronic warfare training.
Federal Communications Commission
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Update: June 2012