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Curing RFI on 2 meters
 from a ViewSonic VX2025WM Computer Monitor

by N4UJW - Hamuniverse.com July, 2014

Over the last several months, maybe even a year ago as I recall, I replaced an older computer monitor with a ViewSonic VX 2025WM 20 inch monitor. As an added note of interest, I recently
had to replace a high speed internet modem just a few days ago with a new one.

The monitor works great and so does the modem and since I am the guy behind the keyboard at Hamuniverse.com, I use them all the time for work (play) on Hamuniverse.com.

I also monitor our local 2 meter club repeater on and off all day long as a general rule of thumb especially during bad or impending weather an almost never change the dial from it. Our club repeater operates on 146.900mHz and I rarely have a need to change frequencies with it due to the workload for the web site. I wish I could be more active on the ham bands but time just does not permit it right now.

I use an Alinco DR-635T dual band radio as my primary radio for monitoring and a 2 meter/440 dual band vertical antenna ground mounted on a short mast only about 4 feet horizontally and about 10 feet off the ground at the corner of the room on the outside of the house that I am in most of the time during the day. I use LMR-200 coax to feed it which is a very short run. So yes, the antenna is at very close proximity to the "station". Transmitting, even at 50 watts FM does not seem to have any issues with the monitor or the computer.

Just a day or so ago, I had some "spare time" which is rare for me and tuned around the 2 meter band channels that I had programmed into memory to see what was going on nearby on some of the other repeaters.

When I came across 146.660mHz, there was a loud alternating "buzz" coming from the speaker that almost covered up the repeater that was in use nearby (about 50 miles away over flat ground). The noise was making the conversation almost unreadable from this very strong repeater! I waited for the conversation to stop and the repeater to cease transmitting. The noise was still there and almost full scale on the "S meter" (bar graph) and the signal strength was fluctuating from about S 5 to full scale in an erratic fashion!!!! (Not a steady signal strength)

I wondered if the noise was on other 2 meter frequencies that I had programmed into memory so I started to tune around some 35 different frequencies within the 2 meter band....sure enough, the very same noise was found on 3 or 4 other 2 meter repeater frequencies but not as strong on the S meter! The noise would change characteristics when changing web pages, web sites, or going back to the desk top, but still there.

So now it was time to revive my RFI troubleshooting skills, so I "woke" them up from a deep sleep from the old gray matter by taking a short break and having a cup of coffee and went to work trying to find the source of the RFI noise that was making listening on some of "my" 2 meter repeater frequencies difficult or impossible.

This is how I found the culprit that was causing the RFI to the 2 meter band.

I had learned many years ago that you could use a hand held "police type" scanner radio to troubleshoot RFI so I dug it out and programmed in the 146.660mHz frequency into it. I now had a poor mans rf "sniffer".

The hand held has a short "rubber duck" antenna so I turned the hand held scanner on and opened the squelch for pure noise and turned up the volume a bit.

Sitting at the desk "shack", at 146.660mHz, the noise was overpowering. I moved the scanner over and around all of the equipment on the desk including the modem while listening to the volume of the noise and moving the antenna closer and further away from each piece of equipment. The noise was so strong, that I could not get any difference in the audio output from it using the rubber duck antenna as I moved it over, around and near the equipment, cables, etc. It was so strong, I would estimate it at many db over S9. The scanner radio has no S meter of any type.

Now I had to dig a bit further into my troubleshooting skills. I knew that I had to de-sensitize the scanner so I removed the rubber duck and replaced it with a 3/4 inch length of solder stuck in the center hole of the antenna connector on the top of the scanner radio.

Now I started my search again using my high tech RF sniffer! (The scanner radio!)

The noise was still there on 146.660mHz but now was much much weaker in volume on the same frequency when I turned the scanner receiver on.

I moved the shortened "solder antenna" attached to the scanner near EVERY piece of equipment on the desk that I thought could produce RFI while listening to the noise for any changes. What I was listening for was a "quieting" or major change of the noise indicating that I was in close proximity to the source of RFI.

The first thing I checked was the new modem resting on top of the computer tower. There was a bit of noise, but not a lot according to the volume of the scanner receiver. There certainly was not enough coming from it to bother with.

Next was the ViewSonic computer monitor. When I moved the antenna next to the screen, the audio increased to almost a pure FM signal..almost full quieting in my opinion! AH HAA!!!!

I then reached over and turned the monitor OFF.....The noise was gone across all of my programmed channels in the 2 meter band! Another AH HAA!

I turned the monitor back on and there it was.....noise again! So just to make sure this was not a fluke, I turned the monitor back OFF....noise gone.

OK! NOW I had narrowed down the "culprit" to the computer monitor that was producing the RFI on 2 meters...at least I thought I had! So far so good.

Using the scanner radio as an rf sniffer tuned to the offending frequency, I now had narrowed down the source of the RFI to the ViewSonic VX2025WM COMPUTER MONITOR and was now in the "ball park", but I wanted to get to a single "bleacher seat" in my hunt for this noise that was creating havoc on the 2 meter band.

If memory serves, this particular monitor has an internal power supply and not a "wall wart" like some do. I knew from experience, that many consumer grade electronic devices can emit strong RFI from their power supplies, especially from "wall warts" on many ham bands from HF through the higher frequency ham bands like VHF/UHF.

I moved everything from in front of the monitor, turned it around and looked at the back of it. Sure enough, an AC power cord was seen going inside the back with a standard 3 prong grounded AC connector attached to the end of the power cord at the monitor case.
While I was able to reach every cable attached to the monitor, I checked that each one was nice and tight..nothing found loose.

My next thought was that if RFI was coming from the power supply, that would be a MAJOR job to take the monitor apart! I did not want to do that except as a last resort so I trudged on.

So my next step was to see if the RFI was coming from either the AC power cord or the "video" cable OR both or maybe from the screen.
I again took the radio scanner with even a more shortened "antenna" of about 1/2 inch long or a bit more attached to the antenna connector and proceeded to place it near each of the "cables" coming from the monitor with it turned ON.

When the antenna was near the video cable, the scanner volume increase by a hugh amount compared to the AC power cord. I moved the antenna away and back close to the video cable several times and the noise level would change every time. I turned off the monitor and again the noise was gone.

So my deductive powers went into play and I determined that what ever the actual "source" of the RFI was, it was coming from inside the monitor and getting on the video cable and being radiated "over the air" using the video cable as an "antenna". Poor or no RFI shielding I guessed. I looked at the video cable carefully and there were no ferrites on it like most have.

I stepped back and thought about this situation a bit and knew I had a choice, replace the monitor, or the cable with a shielded type with ferrites or troubleshoot the video cable. I did not have a spare.

So longer story short, I ordered some snap on ferrites to place on the video cable....you guessed it. A few days passed.....got the ferrites in...tried them at various positions on the video cable...no effect!
Nada, ziltch, no change in the noise being radiated.

Then like a flash of lightning, IT HIT ME!

This "RFI situation" is nothing more than an unbalanced "antenna" that is radiating down the feed line! In this case, the feed line was the video cable coming from the monitor leading to the computer.

Enter the "ugly balun"......!!!!!!

I knew that the offending rfi was in the 2 meter band so all I needed to do was to wind the video cable into an "ugly balun" style coil. The "ugly balun" is not actually a balun, it is an rf choke.  I wound about 4 turns of it into a coil (ugly) about 3 to 4 inches in diameter and secured it with some wire ties from my junk drawer. It was indeed, ugly!

The coil was moved experimentally closer and further away from the monitor coiling the video cable in different locations along the cable while listing to the scanner radio noise...(this takes some practice to keep the coils of cable in the shape of a coil), and at one point not far away from the video connector, the noise completely went AWAY!!!!

Yellow "circle" represents the approximate "ugly balun"
 location on back of monitor. The "ugly balun" coils are closest to you in the photo.

I then secured the coils (ugly balun) where they would not move. See photo above. I then moved the monitor back into its original location on the desk.

After checking the entire range of 2 meter frequencies I had programmed into the Alinco transceiver I found they were "quite as a mouse around a cat" on ALL of them! I did not check any HF ham band frequencies. "Problem solved on 2 meters, hopefully with this simple addition of the choke coils". Fantastic!

The MFJ snap on ferrites were model MFJ-700A4 (Using 2 did not phase the noise. I did not try 4.) This is not to say they are worthless, but they did not help the RFI at all with my particular problem by trying them on both the AC power cord or the video cable using 2 ferrites on each one at the same time at different locations on the video cable.

The video cable (DVI type) coming from the computer and going to the monitor did NOT have any type of RFI suppression or protection built into or on the cables when I first looked behind the monitor. I do not know if the DVI cable is shielded or not. It is a used cable that was attached to the monitor when I got it. Even replacing it with an RFI suppression type may or may not have "cured" the RFI...only one way to find out...get a new one with complete rfi suppression including the ferrites. Have not done that yet.

According to later research done on this particular ViewSonic model VX2025WM, the 1680 x 1050 resolution which I use, usually results in pixel clock frequencies that are between the range of 135 mHz and 154 mHz. This falls within and well above and below 144 to 148mHz...the 2 meter band!

Upon getting into the menu of the monitor, I found the pixel clock runs at 146.300mHz! The monitor is Part 15 compliant! HI HI.

After completing the ugly balun adjustment, I did a scan from 146mHz to 146.900mHz and still noted a few less strong "birdies" on frequencies that I do not use. I DID NOT FIND THE NOISE AT THE PIXEL CLOCK FREQUENCY by holding the hand held scanner next to the monitor screen! I found this strange but did not let it bother me.

I have no way of measuring the intensity of the RFI coming from the monitor so maybe increasing the distance from the monitor to the 2 meter antenna "might" help and is the most likely cause of the severe RFI to the 2 meter radio channels since the transceiver antenna is so close to the "station".

This experimentation "cured" my RFI noise problems on the frequencies that I USE, but you may have to experiment with your setup and change the "ugly balun" coil diameter size, number of coils, distance between coils and monitor on the video cable, etc using the "ugly balun" "cure".

As an added note, it took me a lot longer to "find" and "cure" the problem than it most likely does for you to read this article, but in the long run, it was worth it for me. All of my programmed 2 meter frequencies are now very quite....only white noise is heard on each of them!

I suppose that the proper thing for me to do in the future is to replace the existing video cable with one that is a direct factory replacement and has the installed ferrites already on it, but who is to say that they will work as well or better than the "ugly balun" I used? Moving the antenna further away will certainly help also but that is another project down the road of ham radio adventures at Hamuniverse.com!
Good luck with finding RFI in your computer system and I hope this gives you some ideas to plant in your gray matter garden to help it grow!! 73 - Don - N4UJW

Final note and request...If you have a method of interest to help others cure their "computer rfi" to ham gear on ANY BAND, please let us hear from you. Of particular interest would be getting the exact type, part or model numbers, sources, etc of snap on ferrites known to work well on ANY HAM BAND.  email info to  n4ujw AT hamuniverse.com   Thanks!



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