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

Karin Johnson karinann at tampabay.rr.com
Wed Dec 23 11:14:26 EST 2015

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
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
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
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

More information about the RFI mailing list