General discussion

Locked

RFI Problems

By ajk ·
I have an ECS K7VMA motherboard with an AMD Duron 750 chip. When the system is on, there is strong radio interference on my AM radio reception. I have disconnected all the drives and removed all the cards, CPU fan and the CPU itself without any improvement. What can the problem be? FM radio, TV and other audio equipment are unaffected.

This conversation is currently closed to new comments.

7 total posts (Page 1 of 1)  
| Thread display: Collapse - | Expand +

All Comments

Collapse -

RFI Problems

by B_Pope In reply to RFI Problems

is your modem never your radio or any halagen lights?.they can both cause reception problems.

Collapse -

RFI Problems

by ajk In reply to RFI Problems

Even with the modem removed, the RFI is still there. There are no halogen lights closeby. Both my Dell Latitude and older PII 300mhz PC do not generate any intereference.

Collapse -

RFI Problems

by TheChas In reply to RFI Problems

First, there is likely nothing wrong with your computer.

AM style radio signals (including broadcast TV) are the most susseptable to interference. We cannot watch channel 3 when our computer is on. Our 750 MHz causes less problems than our older slower machines did though.

On it's own, your computer is a very capable RF generator. A look at the radiated energy from most computers would scare most of us.
This is also why you can spy on most computer users with a fairly simple RF receiver.

You need to either shield the source, or increase the distance between the computer and the radio. How much effort you want to put into this, depends on how important using the AM radio with the computer on is to you.

Install ferite beads near the computer on all cables that do not already have them.

Make sure that all slot and port covers are in place, and tight to the case.

Add star type lockwashers to all case cover and power supply mounting screws. This is very important onpainted metal.
If your chassis is painted metal, consider a new case with a plated (shiny) chassis.

Add metal window screen to all vent openings. The screen must be grounded to the case.

CAUTION!! MAKE SURE THAT YOU DO NOT BLOCK NEEDED AIR FLOW THROUGH THE CHASSIS!!

Check your unused drive bays. Install metal plates behind the plastic covers as needed.

Add ferrite beads to the cables that run from the mother board to the front panel.

You can try moving the radio around the computer to find where the interference is strongest, and look for ways to block any paths that I missed.

You might even line the inside of the plastic face plate with aluminum foil.
It may also be your monitor or printer that generates the noise.
Good Luck.

Collapse -

RFI Problems

by TheChas In reply to RFI Problems

After thinking about this, for AM radio frequencies, your power supply or monitor are the most likely sources of the RFI.

There is not much you can do to reduce the noise from the monitor.

If it is the power supply, you might find that a higher power output supply is quieter. Or, the nosie level may vary from brand to brand.

Collapse -

RFI Problems

by ajk In reply to RFI Problems

Some interesting points. When I first started with computers in the late 1960's I used to put an AM radio on top of the CPU cabinet to 'listen' to my program running.

However, the interference can be picked up some 15 metres away on my car radio as well. Neither my Dell Latitude or PI 300mhz systems give off any interference. I doubt that applying the fine adjustments suggested wil affect a signal so strong that it can be noticed so far away. Can it be a poor power supply?

Collapse -

RFI Problems

by TheChas In reply to RFI Problems

Yes, the power supply is the likely source, and easiest to change.

Since you have removed everything else, that is where I would start.

I have noticed that some of the new power supplies are much lighter than older ones. I suspect that they are using smaller coils at a higher frequency to achieve this weight reduction. This may have pushed the power supply noise into the AM band, or at least up near the 455 KHz that is the common AM radio Intermediate Frequency.

So, if you buy a new power supply, compare similar units by weight. Also peer in the slots and see how many coils and caps there are. The larger coils are for the switching circuit. The smaller coils are noise filters. Similar story on the caps.

Collapse -

RFI Problems

by ajk In reply to RFI Problems

I bought a new power supply and it reduced the RFI slightly. It appeared to be of more or less the same weight and qaulity of the old one. I then had a look at my old Pentium 1 system's power supply. It is of similar quality.

When I returned the new power supply to the shop, I took an AM radio with and tested it against some demo systems on display which supposedly use the same standard power supply which they sell. I could not pick up any serious RFI problems. Weird!!!

Back to Desktop Forum
7 total posts (Page 1 of 1)  

Related Discussions

Related Forums