All: Thank you for the replies. First off I've done quite a bit of DF work
regarding power line based intermittent street lights with a great deal of
success. Fortunately the streetlight interference that bothered me the most
occurred with lights no more than a mile or less from my home and antennas.
Since I live in an antenna restricted area, antennas are a bit of a
challenge. Luckily I have a small cypress tree forest next to my home and I
can hide wire antennas in the cypress trees very effectively. About a year
ago I put in a dual band vertical for 80 and 40 meters, which works very
nicely and have been having a lot of fun on 80 CW. Another story there.
Within the past couple of months I've noticed some groupings of discrete
Carriers related to each other but were very weak and not there all the time
on the same frequencies at the bottom end of 80 CW. So I pretty much ignored
Them. Then about a month ago I decided to see if I could find one grouping
around 3518 kHz, which I surmised might be coming from the neighborhood. The
signal levels involved with this grouping is around -90 to -80 dBm as
received on the vertical antenna. I also have a 40 meter dipole located
about 50 feet away from the vertical, and these signals are not readable on
the dipole. I considered that the dipole was oriented so the source of these
signals is probably off the main lobe of the dipole. But this only a guess
since I don't know really where the source is located. So then I noticed
another grouping of the same spectral pattern at a frequency of 3788 kHz,
but this grouping was very strong, about -60 to -50 dBm. So this grouping
caught my eye. Did I mention I love to solve puzzles??? I took a first DF
reading at bearing 110 degrees, then walked to several other locations sort
Of 90 degrees off the main bearing and took some more readings. This got me
to the next street over from my home. I walked to that area and started
taking more readings while watching the directions and also the signal
strength on my Tecsun PL-660, adding attenuation as necessary. While on
that street I think I found the particular house that might be the source of
the RFI, but walking a couple of hundred feet away from that particular
house and taking another bearing pointed me to a completely different house.
I had plotted all of my bearings on Google Earth Pro and they all seem to
converge on the first house that I mentioned above. But the strange part of
this scenario is when I am more physically close to this house the bearings
don't agree. I've had a few conversations with Frank KB4T regarding DF
technique, which was quite helpful. Basically, the advice is "Trust the
Bearing information". As an aside here, I've lots of experience with
EMC/RFI techniques and design philosophy. I've worked for electric
utilities in the engineering field, as well as computer and communications
hardware suppliers over the years, I am also a registered Professional
Engineer.
What is interesting about the stronger signal I mentioned above the spectral
pattern is NOT line locked. In other words if I trigger on line on my
spectrum analyzer (Tektronix 7L12 in 7934 mainframe) the spectral pattern is
similar to Vertical Interval Walkthrough when the TV industry was using NTSC
video. The drift of the spectral pattern is about 1 to 2 Hz different from
the 60 Hz line frequency here. (A sort of educated guess as to the exact
Frequency difference). There are similar spectral patterns offset from the
main pattern by about 31 kHz, both above and below the main pattern. The
extend out to around 200 kHz from the main lobe, but most are very close to
the noise floor of my measuring equipment.
I know these things can be difficult and frustrating to find. As
individuals we don't know every thing there is to know about this world and
electronics and such. Knowledge is an ongoing learning exercise and keeping
an open mind and asking questions can humble the best of us.
Cheers for now,
Karin Anne Johnson P.E. K3UU
Palm Harbor, FL
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