A TechLore "Ask the Experts" Question...
Question:Why do I hear AM radio on my phone, VCR, or TV when used or on mute?
-submitted by tim1996
Answer:Electronic devices are not shielded from the bombardment of outside radio frequency interference. AM signals, TV stations, and other types of broadcasts can accidentally be picked up by an electronic component not designed to receive them.
Here's a simple breakdown: An antenna is a device designed to pick up RF signals. The shape, length, and size of the antenna all play a factor in what frequencies it is likely to receive. A simple antenna can be defined as any metallic object of a given size, length, and shape. So, nearly any metallic object can be considered to be an antenna.
Okay... we got that out of the way. Here's how it affects you. The power cord, internal electronic components, IC chips, metal board traces, and so on can all be considered antennas in the right circumstances. These internal parts, though not designed to receive RF, are susceptable to interference (any thing that interferes with the normal operation of the device).
It goes even further than this, which is why if you look at your manual, you'll no doubt see the following paragraph (or something very similar) somewhere within:
"This device complies with part 15 of the FCC Rules. Operation is subjectThis paragraph is exactly what your problem is talking about. It states that your device should not emit any form of harmful interference (pretty much all electronic devices generate some form of RF signal during normal operation, but steps must be taken by the manufacturer to design it in a way where the device does not transmit it under normal circumstances), and that your device is not immune to outside interference.
to the following two conditions: (1) This device may not cause harmful
interference, and (2) this device must accept any lnterference re-
ceived, including interference that may cause undesired operation."
Since you are picking up AM through your cordless phone, VCR, and TV, it's likely that you live very close to an AM transmitter for a local AM radio station. If this is the case, there may be some things you can do.
- Try spacing, or moving the electronic components to another location.
- Try installing AM radio filters on the electrical connections (a common way that AM gets into other devices).
Also, speak with your neighbors regarding your issue. Find out if they experience similar problems with their equipment. It may help you determine if the problem is where you live, or a problem specific to you.
For more information regarding Part 15 of the FCC Rules, visit the FCC's Website.
Matt Whitlock - Editor, TechLore.com