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RFI on 2 meters
from a ViewSonic VX2025WM Computer
- 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
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
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
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
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
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
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
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.
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.
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
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!!!!
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.
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
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
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
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
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.
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
Nada, ziltch, no change in the noise being
Then like a flash of lightning, IT HIT
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
Enter the "ugly balun"......!!!!!!
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,
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
Upon getting into the menu of the monitor, I found the
pixel clock runs at 146.300mHz! The monitor is Part 15 compliant! 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
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
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
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
Green Geeks Web