RF interference - through the air or wires (screen, signal, sound)

[robertpasa]

I have a Sony radio boombox in my bedroom. When my fridge automatically goes on or off (because of the termostat), the fridge makes a knock sound, and an instant later, a click comes out of my radio. I know it's linked because it always happens this way.

Is this RF interference being sent through the air or through the power lines?

Also, I have a small room fan at one side of my living area, and an old tube TV at the other side. When I turn the fan on or off, horizontal static lines will briefly flash on the screen. Again, is that RF interference through power lines or the air?

Also, why does turning the fan on or off send a static but when it's just running, there is no static?

[kazyn]

Through the power, most likely.... I don't think it's RFI, just a drop or increase in current. Sounds like you might be pushing your house's electrical capacity.

[hoffdano]

I agree it is likely through the power lines unless your radio were tuned to AM radio. AM radios are very sensitive to RFI. Put an AM radio near a computer and you'll see.

When the fan is turned on, a few things happen that could generate "noise" - the arc that occurs when the power switch is turned on, and the tiny arcs that travel on the motor brushes. When the motor reaches speed the frequency of that probably rises high enough that the filtering in the power supply of the TV is not sensitive to it.

A powerline filter might remove the video noise on your TV.

[Pruzhany]

The house has old wiring and probably has a grounding issue. The noise you're hearing is the compressor turning on and off. Might want to have it checked for low coolant or a collant leak. But basically its causing an internal power surge in the home. Depending on the age of the fan, its either electronic (newer) or has a wrapped wire transformer (older) and if its the older type then its sending a signal through the wires.

[harry chickpea]

I'm going to disagree here. If your tv is the old type with tubes, any momentary power glitch is too fast and the power supply and capacitors too solid for it to be an issue. If you saw a shrinking of the picture, then yeah. A scan line interruption is almost always from an air source. The shielding on the pre-amp stages of older tvs can be minimal, and any spark can give enough RFI to show as you describe.

The boombox could be either, but is more likely powerline. The delay is a bit puzzling though. Refer motors commonly have a tiny compressor and a capacitor assisted start, but what you describe sounds more like the effect of a separate starter winding dropping out of the circuit.

[Poncho_NM]

Originally Posted by robertpasa

I have a Sony radio boombox in my bedroom. When my fridge automatically goes on or off (because of the termostat), the fridge makes a knock sound, and an instant later, a click comes out of my radio. I know it's linked because it always happens this way.

Probably/possibly the compressor relay being activated to start the motor. They are mechanical relays and can spark.