AM Noise Filter ?

[kiernanf]

I have 3 desktop computers and but one(the HP Vectra) puts out so much RF noise that I can't hear my AM radio.
No noise on the FM band just the AM band. And no noise from the HP.

Is there some kind of filter I can install on the computers or the radios?

 

[G0AOZ]

First try reorientating the radio to see if you can null out the noise. Is the radio a mains operated model? If so, try plugging it into another mains socket more remote from the computer(s). Is the station(s) you're listening to reasonably strong, as opposed to something a long way away (DX)? A weak AM station will be quickly overcome with even low level local interference...

Check to see which bit of the computer is causing the problem, i.e. boot the computer up without any network, modem or printer cables attached the rear PC connections. Also, with the computer booted up and causing interference, try unplugging the video data cable, and then switch off the mains power to the monitor and see if this makes any difference. Monitors can often be a source of RF interference.

These tests will help you narrow the field down as to where the interference is emanating. It's unlikely to be the keyboard or mouse, but if you've eliminated the monitor and other peripherals, then try this:- Disconnect the keyboard and mouse (with machine switched off) and boot up with a DOS floppy disk. You should now have literally just the mains lead connected to the computer and nothing else. If the noise is still prevalent, then you must look towards the innards of the PC.

First thing to check is that all internal connections are tight and firmly seated. Make sure that all drives, motherboard, power supply, and earthing straps are firmly bolted down as appropriate. Are all the backplates firmly fixed? Fit blanking plates to unused holes. Is the case lid making a good firm earthed connection to the chassis? Make sure ALL the lid fixings are being used.

It's possible that the PSU is responsible for radiating noise back down the mains cable. There are two ways to solve this - substitute PSU for a known good one with up-to-date CE and/or FCC approval markings, or try fitting an in-line suppressor to the your mains power lead. It's remotely possible that you have a rogue video, modem, network, or soundcard, even a hrad disk, but very unlikely. Only substitution will prove this...

I actually hook my computer up to sensitive radio receiving equipment, so I know it's possible to obtain virtually noise-free reception in a computer environment.

Good luck!


ROGER - G0AOZ.