Re: S9 Noise in 40 Meter Band - How Can I Track it Down?
Neil Smith G4DBN
Hi Bill, there is a very strong 120Hz component in the 7045kHz
recording, and also strong lines at 240 and 360Hz. Also weak lines
at 60Hz, 480Hz and 720Hz.
In the 3000kHz recording, there is a very strong 60Hz component, then 120, 180
, 240, 360 and 720Hz
Same artefacts in the Icom recording, but the Icom filtering
reduces the 60 and 120Hz components radically.
In the 14MHz recording, there are also regular amplitude dropouts, but that could be electric fence pulses or something pumping the AGC.
Right, so it is power-line related in some way.
1) First obvious thought is that there is a broken insulator or
faulty transformer on a power line pole somewhere and it is
arcing, but you should be able to use a medium-wave portable radio
to locate that.
2) If there is nothing of that sort within a quarter mile or so,
then the huge level or harmonics could point to it being a
series-wound motor with a commutator, but I think we'd see other
frequencies related to the rotational speed.
3) Could it be a thermostat on a water heater or refrigerator or freezer or aircon which is arcing?
4) It doesn't sound like anything I've heard from power-line communications or broadband internet services. The lack of any obvious modulation doesn't necessarily mean it *isn't* something like that, but usually you only see a 60Hz or sometimes 120Hz modulation on power-line comms.
5) Are there any machine shops or workshops nearby which might
have a rotary phase converter running all the time, or VFD
inverter for three-phase machinery perhaps?
6) Any locals with ground-source heat pumps or well pumps or ornamental fountains or pond pumps for fish?
7) Any 60Hz mains-powered electric fencing units, or bug zappers
or the like?
8) Any solar panel installations which feed the grid? Unlikely
as you would probably see them stop as the sun sets.
Things to try:
1) suspect your own house first. Can you turn off all the breakers and isolate the house power, with the radio/laptop running on batteries to see if there is any difference? If there is, turn each breaker on and see which one makes the noise return and go hunting.
2) when the neighbourhood is very very quiet, late at night when there is no wind, have a listen for arcing of humming noises in the area. Try not to get arrested!
3) If you found a reduction with the loop horizontal, that means the signal is probably in the plane of the loop, but that could mean it is a mile away. Can you get the loop away form the house and see if you can find any nulls? If you can, then move 50 feet and try again, to see if you can triangulate the noise source. It will be along a line parallel to the loop.
I wish you the best of luck with tracing it, Bill. If you can get
a really wide-band recording with at least 16kHz of audio
bandwidth, it might help to dig out any commutator whine, but
would probably be way too low to identify any SMPS. Can you get
snapshot of the waterfall spectrum of DC to 150kHz? Might help to
find a smoking gun if there is something with a faulty SMPS out
On 09/11/2019 23:46, Bill Alpert wrote:
Hi Neil, No structure that I can tell. Just a raspy sound, which is most objectionable in AM mode. No periodic changes detected. Yes, ATT does reduce it.
-- Neil <a href="http://g4dbn.uk/"><small>g4dbn.uk</small></a>