Grand Rapids Business Daily

What could cause a low-pitched hum on my radio when listening to the AM frequency?

It's on every radio in my house, but I don't hear it on my car radio. Also, what could cause my car radio to suddenly change frequencies?

Public Comments

1. those hums you hear are caused by EMI or electro magnetic interference. The same problem occurs on some cordless phones. The dedicated electrical line to your house could have some bad shielding or something like that. As for your car radio, frequency hopping was invented as a way to stop enemies from getting our transmissions in times of war. It is now used in nearly all electronics, such as cell phones, t.v., wifi internet, phones and radios. Your radio may work but have a bad component which is causeing a radio hop that was unscheduled occur.
2. I have the same problem and I found out it was my electronic air purifier that was causing all the interference. These devices use high voltage oscillating pulses that love to get into AM radios, so if you have any of these purifiers in your house, try unplugging them while listening to AM and see if it goes away. You must unplug it from the wall and not just turn them off, as, sometimes the power supplies stay on in these units and they are the noise generators. As for your car's AM radio changing frequencies on its own...sorry to say it could be most any component in the front end of the radio. All 3 sections (RF amp, mixer, and oscillator) in the front end of most AM radios are usually combined into one, single-transistor stage. If you examine schematics of AM radios you will see this fact in the complexities of the circuit. FM radios have 3, separate stages for these functions, but AM, being so simple can operate all 3 functions in one stage.