[RFI] 40 Meter Noise Source Found (sort of)

David Cole dave at nk7z.net
Wed Dec 23 12:24:42 EST 2015

Nice piece of detective work...
Thanks and 73's,
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On Wed, 2015-12-23 at 11:14 -0500, Karin Johnson wrote:
> About a month or so ago I noticed an increase in the noise floor on 40
> meters that was
> of a cycling type nature.  The noise was on for 45 seconds and then off for
> 45 seconds.
> It increased the noise floor between 6 dB and 10 dB, but the source of the
> noise only
> came on around sunset and turned off around sunrise. So it was this
> continuous on/off
> all during the night time hours.  Most of my operating on 40 meters is
> during the evening
> hours, so this was kind of disturbing to me as my antenna is only a 40 meter
> dipole
> very close to the ground because of antenna restrictions (read HOA). Any way
> I was determined
> to find the noise source.  At first I thought it might be a streetlight
> given the timing
> of only on between sunset and sunrise.  Also the 45 second on/off ratio, as
> from my
> experience when some streetlights turn on they arc a bit and if it can't
> fully turn on
> the light turns itself off for a period of time then tries again a bit
> later.  I've actually
> observed this behavior on a few streetlights near home here, which I
> reported to the local
> utility and they fix them.  Anyway I have a TecSun PL-660, on which I could
> hear the noise 
> floor increase.  Initially I did try walking around the neighborhood here
> but was not able 
> to detect where the noise was coming from.  So I ordered a National RF loop
> for 40 meters
> and plugged it into the TecSun.  Major improvement in being able to detect
> the general 
> direction given a first bearing measurement.  I knew the noise could be in
> one of two
> directions from my home.  I plotted the bearing in Google Earth Pro, so I
> could see where
> the next bearing location would be.  The next bearing was taken in an area
> about 90 degrees
> off the first bearing, I'll call this the tennis court location.  But when I
> went to this
> location I could not hear the noise.  Bummer!
> So back to the drawing board.  I assumed that my original bearing could have
> been off by plus
> or minus 5 degrees, allowing for some slop in my ability to read the compass
> reading. So 
> I went back to Google Earth Pro and plotted another bearing line 5 degrees
> off the original
> bearing.  This gave me a "cone" of suspected area in two directions from my
> home.  I was 
> assuming that if my bearing had some error to it, at least I could narrow it
> down to a smaller
> physical location.  This was a good help, because in one of the directions
> from my home there
> was a small shopping plaza.  So with some help from my sister who was
> driving I was watching
> the radio as we approached the shopping plaza.  We parked for a while and I
> did not hear the 
> noise at all.  So the assumption now was the noise was not in this
> direction, and we concentrated
> on the other direction, which was south east from my home.  I also plotted a
> half mile circle
> diameter on Google Earth Pro as I assumed that the noise source was not that
> strong since I could
> not hear it at the tennis court location which was about a half mile away
> from home.
> Now we drove to the south east quadrant of the cone and at this location I
> was able to hear
> the noise although it was much weaker, but I was able to take a bearing from
> here.  Back to 
> Google Earth Pro and when this bearing was plotted it intersected the
> original bearing in the
> vicinity of a horse farm barn just under a half mile from my home.  So back
> in the car and we
> drove over to the barn.  Luckily my sister knows the owner of the farm/barn,
> and as we drove
> up the owner greeted us and as I described what was going on he thought I
> just stepped off
> of a flying saucer.  Anyway after a few minutes, since he knew my sister,
> all was OK I described
> in more detail what we were doing. I don't know for sure if the noise was
> coming from recently
> installed Christmas lights or a ballast in the barn for a fluorescent light.
> There are two 
> large buildings at the farm for horses that have inside lighting at night.
> The barn that has 
> the Christmas lights on it is about 140 feet long and the entire 140 roof
> line had a string of
> lights on it.  I didn't want to press the issue of noise too much as the
> owner wasn't too
> interested in the technical side of things, but he did promise to turn off
> and take down the
> Christmas lighting the day after Christmas.
> So this weekend I'll see if the noise goes away.  I might note that as we
> drove
> up the driveway to the barn the noise got much louder and stronger on the
> PL-660 S-meter.
> So I am pretty much convinced that this was the general area of the noise
> source. 
> My main reason for writing all of this, is sometimes these noise hunting
> expeditions can take
> a good deal of persistence and effort to find the noise source.  My initial
> assumption of this
> particular source being a streetlight was incorrect.  It took me almost
> three weeks to finally
> track down the source.  If after this weekend when the Christmas lights are
> turned off, the
> noise still persists, I'll go back and see if I can help the owner track
> down the noise
> source to a defective ballast.  If it is a ballast it could be a danger
> waiting to happen if
> it overheats to the point of causing damage.  I think that most
> non-technical type folks won't
> realize that.  Hopefully this can be resolved simply by turning off the
> Christmas lights. 
> Cheers to all and Merry Christmas
> Karin K3UU
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