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Computer Generated RFI: One Easy Fix!
Robert Harper (AF0H)
on
February 24, 2006
View comments about this article!
Computer Generated RFI : An Often-Overlooked Solution
After hooking up a RIGblaster and running PSK-31 a while, I got tired of RFI being generated from the Computer. Cutting the audio input volume level from the rig and watching the Waterfall Display, I still had peaks at selected frequencies coming in to the computer - which is about 3-feet from the rig. Also I had noticed that I had more noise in the receiver with the computer simply turned on and running - and this noise was gone with the Computer shut down.
Remembering the `old and often-overlooked' rules about grounding, I decided to experiment. With no audio going into the soundcard coming from the rig, I watched the Waterfall Display when I touched a ground wire to the back of the Computer case - actually the power supply frame. The noise peaks were gone! Just to make sure, I turned the audio back up (going into the soundcard) and listened to the noise and watched the noise peaks coming in along with the Receiver signal. Again, I touched the ground wire to the PC's power supply case, and the extra noise (and peaks) were gone.
I feel it necessary to mention that the ground wire running to the PC is the common ground shared by the rigs, equipment, etc - the common shack ground.. I found no ill-effects on anything during transmit - even with the Amplifier on. Occasionally, I would have the computer act-up when running the Amplifier and everything running, but not now. Problem solved…
I can't help but wonder how many others have had the same problem and overlooked this simple step - which made such a difference.
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Computer Generated RFI: One Easy Fix!
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by W4CNG on February 24, 2006
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I had an issue with a Video Monitor Extension cable when I first tried to get set-up on PSK-31 a few years back. The computer was on the floor under the desk and the monitor location required an extension cable to reach. A little aluminum foil wrapped around the Extension cable and grounded to the computer case did the trick. The antenna was in the Attic 18 feet above, which had no problem hearing the radiated video hash from the computer. Now in the Terrace Level 35feet from the antenna and a Laptop on the desk, no more issues.
Steve W4CNG
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RE: Computer Generated RFI: One Easy Fix!
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by K3AN on February 24, 2006
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How do you actually ground the common ground wire- via the green AC outlet wire? Via a ground rod you installed in the soil? Both? Neither?
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RE: Computer Generated RFI: One Easy Fix!
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by K4IA on February 24, 2006
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I ran a strap - just like every other piece of equipment - from the case of the computer to the common point on the back of my antenna tuner. There is one strap from there to the grounding rod system.
Attach to the computer case with a large washer and star type lockwasher to "pin down" the strap. If you have to, sandpaper the paint off the case to get a good connection. I put a longer screw in an existing screwhole on a bare piece of metal. Check to be sure it is really bare and not painted silver. And be careful the screw is not too long and touches something indside the case.
This has also helped keep RF out of the computer although you may find you still need ferrite chokes on all the cables.
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RE: Computer Generated RFI: One Easy Fix!
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by KC8VWM on February 24, 2006
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Yup, been saying that for years... It really works.
"When you can't beat em, join em together and see what happens."
73
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RE: Computer Generated RFI: One Easy Fix!
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by AA4PB on February 24, 2006
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I submit that it is not an "earth ground" that made the difference but rather that you provided a low impedance path (the copper strap) between the computer and the radio. Most of the noise currents now flow thru the strap in lieu of the higher resistance shields of the audio lines. In any case, it is a good solution.
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Computer Generated RFI: One Easy Fix!
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by K1CJS on February 24, 2006
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If it works for you, good! But..... Yep, there is a but--every case (no pun intended!) is different. There are times that extra grounding won't make much difference at all.
I had a LCD display that caused me no end of problems, RFI, strange noises, etc. that no amount of grounding would cure. It was just a case of noisy display panel electronics--from a too cheap display. I went back to my old display (a CRT type) and the noise was gone.
As we are sometimes accused of being, and sometime very correctly--hams are cheap and tend to do things (that we can do and other non do-it-yourselfers find it hard to do) that somehow continually point that out! :-)
BTW, Don't get me wrong--I am glad you were able to solve your problem. 73!
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RE: Computer Generated RFI: One Easy Fix!
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by K8MHZ on February 24, 2006
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I'm happy too....
But, when I tried to supress noise coming from a laptop with a long cable to a wireless adaptor, the hash got worse!
Nothing other than shortening the cable to the adaptor made any difference, which solved the problem. I can't have the computer where I want it, but it is within 5 feet of it.
Next stop is the desktop.
Nice article,
73,
Mark K8MHZ
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RE: Computer Generated RFI: One Easy Fix!
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by WB4OMM on February 24, 2006
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I had a similar problem of RF hash, but only on my transmit audio. Weeks of playing with grounds, moving stuff, chokes, shorter cables, ad nauseaum, with no resolution, not even a change in the level! Finally, I resorted to (what we all know should have been my first step) "unplugging" one cable at a time and transmitting. STILL had hash. Disgusted and frustrated, I unplugged all the cables and quit for the day. Next day, I put everything back - but forgot to re-plug my PTT footswitch into the rig. When I tried to use the footswitch in a QSO (didn't work) I hit the "xmit" button on the rig, and voila! No hash. Reconnecting the footswith and transmitting - lots of hash - remove the footswitch cable, all gone.
I replaced the zip cord type two strand with a single conductor with a shield, and the problem disappeared. I never would have figured a control wire would be the culprit.
Hope this may help someone in the future.
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Computer Generated RFI: One Easy Fix!
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by KG6WLS on February 25, 2006
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I use a laptop computer for PSK31 and HRD for rig control as well. When using PSK, I was getting all kinds of junk on my audio and the waterfall. Found the culprits. One Radio Shack wall wart and the power supply/charger to the laptop. Unplugged them both...problem solved.
73
Mike
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RE: Computer Generated RFI: One Easy Fix!
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by W6TH on February 25, 2006
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.
Nothing new to me as I have been doing the same since computers were all vacuum tubes.
Do you recall vacuum tube gadgets, which now are called gadgets that glow in the dark?
Oh! Maybe someday I will write a sketch of how a brute force filter works.
73, W6TH
.:
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Computer Generated RFI: One Easy Fix!
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by WF7A on February 25, 2006
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I once elmered a Novice who had a similar RFI problem. When I told him that he had a floating ground, he looked up at the ceiling.
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RE: Computer Generated RFI: One Easy Fix!
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by NS6Y_ on February 26, 2006
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It's amazing how much junk poorly shielded cables can recieve or xmit. I was testing some accelerometers and put together a Microdot to BNC cable to do so, but on my scope all I could see was horrendous noise! I realized that cable needed much better shielding and made a much better one with good HP coax, and could see the signals clear as a bell.
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RE: Computer Generated RFI: One Easy Fix!
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by KB9YGD on February 27, 2006
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Hi Bob,good article.Well i had an rf problem with rf getting into the xmit audio and i got the split type ferrites and put them on all the cables in and out of all the radios and computers router modem and tx line and it worked very well.73,Norm.
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Computer Generated RFI: One Easy Fix!
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by N5UV on February 27, 2006
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Tnx. for the quick tip...I started ground EVERYTHING in my shack to a ground bus a year ago and saw a great improvement on my waterfall image. Only thing I don't ground is the interface, since I've heard that tends to create a ground-loop for some PSK31 ops.
CU on the waterfall de N5UV
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RE: Computer Generated RFI: One Easy Fix!
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by W3BC on March 7, 2006
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Back in the day, us old geezers used to say:
Ground everything in sight.
If you can't ground it, bypass it.
If you can't bypass it, shield it.
If you can't shield it, forget it.
73
//Joe
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Computer Generated RFI: One Easy Fix!
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by KN4LF on March 8, 2006
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I tried your suggestion to ground my computer to the station ground system and all of my computer generated QRN went away. I had presumed that the opposite result would occur!
I also discovered that if you ground your noisy switching power supply you will get the same positive result.
--... ...--,
Thomas F. Giella, KN4LF
Retired Space Plasma Physicist
Lakeland, FL, USA
Grid Square EL97AW
kn4lf@arrl.net
KN4LF Amateur & SWL Radio History: http://www.kn4lf.com
KN4LF 160 Meter Propagation Theory Notes: http://www.kn4lf.com/kn4lf8.htm
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Computer Generated RFI: One Easy Fix!
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by NB2A on March 23, 2006
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I appreciated your suggestion about grounding the PC to the rest of the central ground system you have. I have not had the same result though doing this. I guess like on the of the comments were here each case turns out to be individual. I have had two RF issues surface as of late one being computer generated traced to be on the sound out from my sound card to the patch in on my FT1000 MKV recommended point for audio in with computer and digital applications.
It seems then in TX only the low level whining type noise is a pain. It disappears as soon as the computer is off with no change if monitor is on or off either.
I have tried grounding as well as chokes as stated no change at all.
It is the type of noise I guess one could live with but since I am a bit of audio phile if you will it is not acceptable. I run EQ and clean audio otherwise so I am determined to get rid of this. It seems though from what I have concluded so far its the computer itself an E machine by gateway the issue. The case is plastic which is in itself is garbage to work with.
The one other RF issue I am working on is with a HF2V 40/80 antenna and using my HF amp.
I guess the more you add to the shack the more you have to deal with simply.
73s
NB2A
http://www.geocities.com/nb2a/NB2A.html
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