What is causing those squeels when your near a station but not right on it?

 

With my HF radio equipment, I've often heard these pure oscillations when I tune through any of the bands. I believe that this is caused when people are tuning their radios. But this is HF, what frequency are you referring to?

Austin

 

AM or FM? I'm betting AM. It has to do with sidebands being mixed (heterodyned) incorrectly.

 

Electronerd, I think the squeel I'm talking about is common to most Am broadcast band radios. That's the frequency I am refering to. Also, commercial Am is the mode of modulation I am refering to.

 

Bill, you're right, it's AM. But I'm not sure what you mean by incorrect mixing.

 

Think about how an AM dial is organized, every 10Khz there is a station, some far, some close. If you tune a dial between two stations their frequencies will heterodyne together, but not as a stable sound. Hence the squeal.

Visualize two AM frequencies on a spectrum graph and you get the idea.

 

Thanks. That makes sense.