DFing at these frequencies is more art than science; I can locate
a source to an individual house, but it takes taking a number of
bearings as one 'walks the sidewalk' on the opposite side of the
street.Eventually it becomes clear what direction the signal iscoming from
based on the loop's null direction always (more or less) pointing to the same
house. Maybe this step was short
changed?
There is another factor to consider too. My top DF frequency
is 4 MHz in the portable gear I use (a marine DF receiver with
built-in ferrite loopstick and short whip "sense" antenna.) DF
operations should take place outside the distance of 1/4 wave
length "near field" of the source to assure a (somewhat) "plane
wave". Close to a source and loop antenna DF nulls and the
"sense" feature get quite ambiguous and misleading.
Some gear is equipped with a "sense" antenna. A sense
antenna allows one to resolve the 180 degree ambiguity issue a
loop by itself has. Not every DF loop/DF apparatus has a "sense"
function. There a couple hand-held military DF loops for VHF
low-band DF use that have "sense" functions, and those
antennas can be used with any 30 - 50 MHz receiver.
Again bear in mind what a quarter-wave is for the DF
frequency presently being used: 128 ft for 160m, 64 ft for 80m,
32 ft for 40m and so forth (distances are approximate; note
the relationship to the powers of two/binary MS-bit. This is
simply a handy memory trick!)
We went through the exercise of locating a 'noise' source
in a residential neighborhood mid 2019. An inquiry at the
door about 'radio noise' and the noise just went away later
that day. This was on 80 meters.
de AA5CT
.
.
On Tuesday, January 7, 2020, 12:32:57 PM CST, Karin Johnson
<karinann@tampabay.rr.com> wrote:
Hello Group:
I would be interested in emailing/speaking with anyone on the this list
directly, who has had some personal experience with Grow Light RFI.
Rather than take up bandwidth on this list. I have a specific Spectrum
and signal grouping that could be grow lights but am unable to positively
nail it down to a specific home. Rather there appears conflicting direction
finding bearings when I get close to the source. I am using NationalRF
loops For 3 to 8 MHz. Besides that I am reluctant to go knocking on peoples
doors right now. From what I have seen on the NK7Z screen shots they
don't exactly correlate to grow lights. I can supply audio and spectral
plots to enable a discussion. Just to close this missive, the time
for ON/OFF seems to correspond to a high powered grow light.
Regards,
Karin Anne Johnson K3UU
Palm Harbor, FL
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