Do all three actions, look over Jim's papers, get a linear power supply,
and move your loop as far from anything as possible.
Many years ago, while vetting the use of a loop as a RX antenna, I did a
few tests moving the loop further and further from my home and watching
the RFI levels.
Unfortunately I did not document the process, however, the general gist
of the testing was to move the antenna far, far away from all noise
sources, which of course makes perfect sense. I was not aware at that
time of just how much RFI a home can generate... A lot!
I do remember setting the loop up in my kitchen, getting an S9, or
higher noise level, then moving the loop to the deck outside, and
getting far less RFI, something like S5, or S6, then moving the loop to
the backyard, 60 feet from any RFI sources, out in the middle of a
grassy field, and getting an S3, or S4 noise level... All using the
same length of feedline.
That taught just how much RFI a home can generate, and that is worth it
to move antenna as far as possible from all structures.
73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources
On 4/3/21 6:03 AM, David Gottschalk wrote:
Thanks Jim.
Some others have also already suggested a linear power supply. I'll
probably try that, but I'm strongly considering just moving my antenna much
further away from my house, so I can spend less time trying to kill RFI.
On Fri, Apr 2, 2021 at 8:49 PM Jim Brown <jim@audiosystemsgroup.com> wrote:
That's because it's a switch-mode power supply. What voltage and
current? Depending on that, it may be possible to re-purpose an old
linear wall wart. Also, study my tutorials on chasing and killing RFI.
They include specific advice on subbing the linear supply.
Text: http://k9yc.com/KillingReceiveNoise.pdf
Slides: http://k9yc.com/KillingRXNoiseVisalia.pdf
73, Jim K9YC
On 4/2/2021 5:15 PM, David Gottschalk wrote:
I'm wondering if anyone has had success finding a wall wart for a
Raspberry
Pi that doesn't make horrific RFI on HF (or really any switch mode power
supply that isn't noisy!)
I recently discovered the wall wart for my Raspberry PI (that is mounted
outside in a water proof enclosure for my 4G internet) is making S7 level
noise on 80m. Unfortunately, my 80m loop is currently pretty close to it.
When the PI is battery powered, or off, it's S4 noise level here (This is
in the middle of the day). 60m also seems to be severely affected as
well.
I found this on Amazon, but it seems like it's more of a AC line
conditioner, but might be worth a shot. Any feedback would be greatly
appreciated.
https://www.amazon.com/iPower-Supply-International-Travel-Adapters/dp/B01GNNXP0Y?ref_=ast_sto_dp&th=1
73,
David
KN4ZKT
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