How about a photo of your small loop...
73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources
On 1/4/22 20:07, Don Kirk wrote:
I work hard keeping my noise floor on 160 meters low and hopefully equal
between my 3 different pennant RX antennas that point 40, 160, and 300
degrees from my QTH. This winter I've struggled with an increased noise
floor on my 40 degree pennant, and a few weeks ago I located a power pole
that was arcing badly and this pole was subsequently repaired as I
mentioned in a previous post. The noise level on my 40 degree pennant came
down substantially after repair of the pole, but I noticed it was still
higher than my 160 and 300 degree pennants as well as its historical level
by about 3 or 4 dB. Yesterday I tracked the cause of the 3 to 4 dB
increase in my noise floor to a home 0.22 miles away, and this afternoon I
worked with the homeowner to quickly identify the root cause of the problem
which turned out to be a power supply running the lights on his small
indoor Xmas tree located on the second floor of his home.
I once again used a very small loop to sniff each circuit breaker in his
circuit breaker panel to identify the suspect circuit, and when we shut off
the suspect circuit breaker the RFI vanished. The homeowner then unplugged
one device at a time from the circuit until we found what device was
generating the RFI. Finding the suspect circuit took about 30 seconds
using my sniffing loop, and then it took about 10 minutes to figure out
what device on the circuit was the root cause of the problem.
I can't stress enough how important it is to not try and guess what device
is causing the RFI because the homeowner was pretty certain it was due to
his recent addition of a blower fan that he installed on his fireplace, and
he even had me worrying about how difficult of a fix it would be if that
was indeed the case as the wiring was within his walls. I told the
homeowner I never guess what device is causing the RFI because the problem
is almost always different from case to case, and after we were done he
fully appreciated my comment. I use my laptop SDR receiver a lot to
visually see what's going on (behavior of the RFI), but I don't use it to
guess what the guilty device might be except for trying to determine if the
RFI might be power line related RFI.
Using my small loop to sniff the circuit breaker panel is definitely a game
changer for me, and it sure makes working with homeowners a much
simpler task (very efficient, and least intrusive to the homeowner).
Here is a link to a video documenting this case for those interested:
https://youtu.be/J6OjwTRNIvY
73, and Happy New Year.
Don (wd8dsb)
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