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Author Topic: Computer generated noise on radio  (Read 1007 times)

Posts: 3

« on: October 23, 2005, 02:18:31 PM »

I'm trying to use my computer to control and log with my K2/100. As soon as I turn on the power to the LCD monitor and then the computer I get an S2-3 noise on the radio. The radio is grounded through the apartment's electrical system. (Being on the third floor makes it hard to run a ground stake and wire.) I've tried touching a wire from the radio ground to the computer ground with no decrease in noise. The ground seems to be good enough in that I don't have any TVI problems. If I use my laptop there's no noise until I plug in the power cube. The problem is the laptop computer's battery doesn't last that long.
Can anyone tell me what to try to eliminate the noise? Would a better computer power supply be less likely to generate noise? If so what do I do about the LCD or laptop supplies?
Any help will be appreciated.
Tom A61.WA7DET at

Posts: 34


« Reply #1 on: October 23, 2005, 04:40:23 PM »

Hello Tom.  Sounds like this could be coming from several potential problems.  However, I would always maintain a common ground among equipment - always.

First question, you say you get the noise when you switch on power to the LCD monitor and then the computer.  When exactly does the noise start?  Is there noise if you only turn-on the monitor?  

You can hook your monitor to the external monitor port on your laptop to further eliminate the monitor from the list of suspects.

If you can't hook it to the laptop, applying external power to the monitor with the computer off.  If your monitor power cable plugs into the computer (and it is 115VAC - check manual to be sure), try applying an external power source to the monitor with the computer off.

Assuming no noise with the computer off and monitor on, I would first take a look at the power supply within the computer.  The switching within the power supply can generate RF emanations radiated by the power line.  If that is the case, it may be possible to add an EMI filter.  Many power supplies come with these filters already installed, and they are part of the power receptacle within the computer.

There are a lot of potential EMI generators within a computer.  Try plugging the computer and monitor into a power receptacle on a different circuit from your rig as power lines are great radiators by themselves.

Search the ARRL site for EMI and you will find additional theory behind EMI.

Not much to go on, but I hope this is a starting point for you.


Posts: 3

« Reply #2 on: October 23, 2005, 08:20:10 PM »


I hear the noise with just the monitor on but when I then turn on the computer it gets louder. So both item are causing EMI. The computer power supply was purchased on the economy here and is a very cheap one. I doubt it has any filtering but I don't know for sure. I have a CoolMaster supply on the way home and my wife will forward it to me here in the UAE.
I think the computer is on one outlet from the kitchen and the radio is on the outlet in the livingroom. They might be the same circuit though. I'll have to check when I get home.
I'm using an Astron switching power supply to run the radio and there's no noise or birdies that I know of.
I wasn't sure about hooking both grounds together. The serial cable from the radio to the computer doesn't have a common ground. It is custom made per the Elecraft instructions and I wasn't sure if I would cause a problem with a permanent ground connection.
One easy option that I've thought about is building a linear supply to run the laptop. That might be easier than finding the cause of the problem.

Thanks for the help,

Posts: 2


« Reply #3 on: November 13, 2005, 07:27:19 PM »

Sorry to change the subject.

Has anyone had any experience/problems with high-power
amps and wireless keyboards/mice ?

Jack, NN6XX at operamail dot com

Posts: 59

« Reply #4 on: November 29, 2005, 04:57:38 PM »

I use a battery powered AM receiver in the same room with my computer. I notice a similar effect, when I turn on my flat panel monitor significant noise picks up in the receiver. I have to move the radio a few feet away and turn it (internal ferite antenna) to null out the noise. This indicates that the problem is not conducted through the house wiring. Also the noise drops with separation distance. If your EMI and mine are from the same source it probably isn't the power supply. My computer is a new Dell with no modifications.
I am planning to put my HF rig in this room, your post has be worried.

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