Recently our shop purchased a building and built our first new warehouse and office. I noticed the other day I can not receive AM radio stations while my computer is on. It doesn't matter what circuit I plug the radio into. No matter where I move the radio I get nothing but noise. When I shut down the computer reception is crystal clear. This only affects AM reception, FM comes in fine with or without the computer on.
What are common causes of noise aside from crappy PC power supplies? I'm wondering if this may indicate some problem other then a noisy power supply.
Any cheep easy suggestions to clear this up? Service is 3-0 120/208V and the noise is on all phases all circuits not just the circuit the computer is plugged into. I am not very familiar with things like noise, harmonics, etc. So I am not sure how to go about trouble shooting or correcting the problem.
I know the boss wont care about radio reception when he gets back but I can't sit in a dead silent office and work. It drives me crazy. I can't back a trailer with the radio on, but I can't do bids without a radio. Strange isn't it?
I think a good first step is to take a battery powered radio in abd check various orientations relative to the computer. I listen to AM talk at lunch time with my little Walkman part way into my top desk drawer. All the way out and I get the noise from the desktop. All the way in and I block reception. Moving the radio around the case can give you an idea of where the leakage is coming from. You could try to improve the RF shielding and grounding in the case. Any exterior plastic that doesn't have a metallic coating inside would be suspect. But using the little radio to find a sweet spot should help. Some buildings pretty severely attenuate radio signals and the station received signal strength relative to the noise amplitude has a great effect too.
Joe
Using the battery powered radio will also tell you if the interference is coming through the AC or over the airwaves.
I listen to shortwave at home and the interference is something else. Somewhere in my neighborhood is a source of static that is being carried over the AC lines.
It is probably from a bad transformer or insulator, or maybe a neighbor has a bad ballast. I can walk along the street with a portable radio and hear the static as long as I follow the overhead powerlines.
A lot depends on the number of layers on the system board and if it has a ground plane. I know I never had a problem with AM radio on my desk at work and I had 2 IBM PS/2s running in my office 24/7 one in a wood case.
http://esteroriverheights.com/electrical/woody.jpgSome lesser "clones" would affect my radio whenever they were on in the shop around the corner from me (covers on helped a little).
I didn't think anyone still listened to AM radio apart from Radio Hams and those of the religious persuasion.
What I would try is an in-line Mains filter, that your radio plugs into and then the filter plugs into the wall.
AM radio suffers with computers, because of the internal ferrite aerial rod and the fact that computers have so many harmonics that occur in the AM Broadcast band.
One other thing you shouldn't forget is the fact that radios are built to a price these days and have been for some years, any sort of RFI rejection circuitry, is usually the first thing to be tossed out of the formula, in the name of "affordability".
I have not run across this particular problem as yet ...
AM radio in the USA is largely extinct, with the exception of 'talk radio.' My local dial also - if you look hard - carries a sports station, a religious station, and two Spanish-language stations. That's it - a far cry from the full dial of music you could find in the 60's.
In the past year, some legal issues were resolved, with the result that you can get "streaming audio" of most radio stations on your computer.
I run into this problem a lot. First, you can listen to most radio stations online, a good solution. But, as far as the computer goes, most noise is RF, although the power line will help radiate it. Make sure its not the monitor. Flat screens are noisier than CRTs just cut off the monitor, see if the problem goes away. Also the monitor cable, many are poorly shielded. Most RF noise I find comes from 3 sources. One the monitor &/or its power supply. Two the video card. and three the microprocessor or its power supply. Try some clip on ferrite chokes on the video cables (both ends) and power cords on both the monitor and computer. If the computer is plugged into a UPS check that. They will also radiate. Robert
As far as AM radio being dead in the USA, Rush Limbaugh just signed a contract extension for $400 million with a $100 million signing bonus. I guess from that amount of money, somebody either is listening, or that is one hell of a good way to launder money.........
What you are most likely suffering from is radiated EMI (ElectroMagnetic Interference).
PC issues.
1) Check the PC for missing card slot covers.
2) The screws for the card slot covers are screwed in.
3) The PC case screws are fully screwed on.
4) Using a grounded power cord.
5) Verify noise source is PC and not monitor.
6) Perhaps the noise source is not the PC but something else that is plugged into the same outlet strip. What else is turned on when PC is turned on? Things like fans, speakers, desk lights, network switches and hubs, etc.
7) Serial, Parallel, and Ethernet ports are often sources of interference.
8) Do you use any wireless connections like mouse, keyboard or network?
Power issues.
1) Ground pin of outlet actually connects to ground.
2) Radio power cord is fully uncoiled and not running parallel to PC cables.
Good Luck in isolating the source of the interference. Once the the source is found, then we can provide better means of reducing or eliminating it.
Larry C
Rush makes so much money because his advertisers know he has assembled a group of people who will believe anything.
Let's not go down that road, Greg.
Sorry Mike I thought this was a topic about noise on AM radio. My apologies.
Rush is fine as long as you understand it is just entertainment ... like Jon Stewart (Daily show), Letterman or the Roadrunner.
Rush will point that out
The source of EMI from PCs is the PC itself. With speeds faster than 1GHz, and bus speeds ranging from 100-200MHz and cables and copper interconnects (read: antennas) all through the PC with speeds of MHz to GHz, there is all sorts of broadband radiation just waiting to escape. There's very little you can do about it.
PC monitors can also give out tons of EMI. This is easy to check- just turn off the monitor and see if it stops. I had a huge argument with one of my coworkers once due to high-audio frequency EMI interference. The problem was that I was the youngest in the office by 10 years and nobody else could hear it! Was this ultra-high-pitched squeal that was driving me nuts, and he was insistive I was making it up and refused to do anything about it, until a team of fire inspectors came through and the youngest of the group, a 20-something new hire, commented on it, too.
In this case, all we had to do was change the refresh rate of the monitor from 60Hz to 70Hz and it pushed the EMI out of my audible range where it was no longer annoying. I swear it still gave me headaches, though.
Well, the question is moot now but...here goes a long ramble...
Turns out it is defiantly not on the power line it self. Couple days after my original post I had a chance to stop and think about the radio again. Didn't have 6 D batteries handy so I grabbed a 100' extension cord. Plugged into the same receptacle as my computer and took a walk. the reception on the radio cleared up about half way into the parking lot. So my computer radiates noise for about 50' - 60' from the actual tower. It is definitely the PC itself. Monitor, printer, ect makes no difference. Everything is good as far as the slot covers, grounding, ect.
In the mean time the boss is back in the country and was able to get AT&T to fix our DSL so I am streaming AM now and can once again work without having to listen to myself think.
What direction would I go if I wanted to squash this noise? I'm curious how you would go about preventing the PC from radiating such noise. I'll guess one option would be lining the tower in a material that blocks/absorbs the RF radiation. What other methods could I try?
And for those AM radio pundits in the crowd...I listen to Armstong and Getty in the mornings from 6 to 10. Some times I Listen to Clark Howard from 10 to 12. Other then that AM radio in my area drives me crazy. 12 to 6 is split between Dr Laura and Michale Savage they both grate on me a bit and I only listen if I'm really in the mood or my MP3 player is dead. Weekends are really hit or miss. Some good gardening shows occasionally and one tech show. I like click and Clack on NPR but that's only because I used to read their newspaper column as a kid. Happy now? I admit I'm a little off but FM radio just really pisses me off. If I want music I'll fire up my MP3 player and listen to what I want.
Thanks Guys the responses were great!
The more I work on the office side of the business the more I realize how good I had it in the field. So much easier running work and even easier being "just" an installer. I really long for the days of being an apprentice when everything was new and exciting. Such is life...grass being greener on the other side of the fence.haha
You could try overclocking (or underclocking) the main system clock of your computer. It'll most likely be in BIOS as the front side bus frequency- try shifting it up or down 1-2% and see if that changes your radio at all. This won't eliminate the EMI, but will change the fundamental frequency and possibly shift it to a channel you don't care about. Then again, you don't know what's causing the EMI, and changing the system clock should change the ram, FSB, PCI and AGP busses, won't necessarily effect all the other components.
Double-check the case grounding, too. If it's good, try a supplemental grounding electrode of some sort, connected to a good grounding electrode with as short a cable as possible. Conventional ground wires are extra-especially lousy at dissipating ground voltages much above 60Hz since impedance at higher frequencies is so high, and if it's a long path to ground, it may just be harmonics and noise building up on the case.
Sometimes the shielding on the computer case itself is adequate, but a lot of noise is escaping by way of radiation from the cables connected to it (keyboard, monitor, USB leads, etc.).
A turn or two through a ferrite toroid as close as possible to the computer can sometimes help, although you need to be prepared for a lot of experimentation.