AM Radio Interference

[ianbell]

I've noticed that when my PC is running that AM radio reception on my stereo in another room is destroyed - can a PC generate AM interference through the house wiring? or is it somehow broadcasting? I have the sides off the PC tower at the moment if that makes a difference and my stereo is hooked up to an old fashioned rotator type antenna.

[WillyW]

I've noticed that when my PC is running that AM radio reception on my stereo in another room is destroyed - can a PC generate AM interference

Tons of it.


Have you tried tuning around?   Is the interference present over the whole band,  or just on one frequency?


Has it been this way for a while,  or is this something new?

Added any new hardware, or even changed anything?  on your pc,  lately?

Changed the antenna feedline or antenna location, or the location of the receiver lately?

through the house wiring?

Possibly.

or is it somehow broadcasting?

Possibly.

I have the sides off the PC tower at the moment if that makes a difference

If your pc was radiating, I'd expect this to make the interference worse.

and my stereo is hooked up to an old fashioned rotator type antenna.

Easy thing to try:    Coil up the power cord that feeds your pc.   Use a rubber band  and/or scotch tape to hold it in shape.     See if that makes a difference.

Other thing to try:  Ferrite beads.    If it were me, I'd go to some geeky radio hardware type friends and ask.   For you,  -  you might want to try googling for them.   Somebody, somewhere should sell them.    If they are cheap enough, it would be a good experiment.

Both of these ideas are attempting to stop RF from getting out on the power cord of the pc.

You could try them on the power cord of the AM reciever too.


By the way,  are you using either a surge protector or a UPS for the computer?     If not,  borrow one of each and try them.    Especially the UPS.

If you suspect that the pc box itself is radiating  ( do you have a portable hand held battery powered AM reciever that you can hold near the case?)
be sure the case is properly grounded when the computer is plugged in to the wall.   

Could be a lot of ways to lose ground.   The third prong on the power cord plug is ground.   Maybe the wall socket has lost ground?      Maybe somehow inside the power supply it has come loose?     ( Caution:  if you are not technically savvy on the workings of power supplies,  it is best if you do not open the unit.  There are harmful voltages in there. )   

Pull the plug from out from the wall before doing any looking around!


Are you using an extension cord?    Try a different length.   In effect - meaning try a different length of power cord.     You could have accidentally achieved some kind of resonant length.

These are just a few things that come to mind.

Keep us posted.

[macdad-]

well there are several factors...
1st is that ur proccessor is running at the same frequency(MHZ) or that ur
sys bus is running at the same frequency(MHZ) that may involve interference but i suggest just to put the cover over ur comp.

[WillyW]

well there are several factors...
1st is that ur proccessor is running at the same frequency(MHZ) or that ur
sys bus is running at the same frequency(MHZ) that may involve interference but i suggest just to put the cover over ur comp.

Off the top of my head, the AM broadcast band in the U.S. is roughly 520KHz to 1690KHz.

That's "K",  not "M"  hertz.       
I bet his processor is faster than that.     


There are some timing chips on mother boards that are much lower,  but I thought they are still above the AM band. 

What I don't know off the top of my head, is what sort of freqs the switching power supply uses.

[macdad-]

yea probably. ur comp is not the problem.

[ianbell]

yea probably. ur comp is not the problem.

Thanks for the helpful suggestion [ not including the above] and I will wade through them as time allows - I can say that grounding is not the problem; the PC is hooked up to a surge protected power bar; the problem is right across the AM range with the particular station I first noted being 740AM.  I don't know if it is a new thing or not as I never used to listen to AM before!

[WillyW]

Thanks for the helpful suggestion [ not including the above] and I will wade through them as time allows - I can say that grounding is not the problem; the PC is hooked up to a surge protected power bar; the problem is right across the AM range with the particular station I first noted being 740AM.  I don't know if it is a new thing or not as I never used to listen to AM before!

I hope I stumbled across something that helps!   


Just re-read your first post.
You mentioned old fashioned rotator type antenna.      I was about to ask you if it is possible to move the AM reciever's antenna farther away, or at least rotate it 90 degrees,  when I rememebered you'd mentioned the antenna already.

Is that an outdoor antenna,  like up on a pole?     If so,  then it already is far away from the computer.   
Then how about the feedline?    from the antenna to the receiver.... is it in good shape?   Proper connectors?      We're looking for it to not be leaky,  to  not let in extraneous junk.
....  just another thing to consider.

[homer]

- I can say that grounding is not the problem

just out of curiosity, have you checked to make sure that the plug itself is grounded?

[ianbell]

[Just out of curiosity, have you checked to make sure that the plug itself is grounded?
[/quote]

I rewired the whole place last year with new 14G 3-wire copper and put in a new ground at that time [five foot piece of  3/4" rebar straight down] including grounding the copper water pipes, the antena pole,  the trailer frame [did I mention I live in a Mobile Home] and lightning conductor.

[hiloed]

Look for an RF-snap Toroid Choke also known as ferrite bead choke. There are lots of them around.

They are specifically for blocking RF interference. Google it.

You might read these:
http://en.wikipedia.org/wiki/Ferrite_bead

http://computer.howstuffworks.com/question352.htm