Thanks for the help. As luck would have it, right now we seem
to be in monsoon season. Rain every day for the next 2 weeks.
It will give me time to build the DXE version of your antenna.
I did spend a lot of time driving along the road with the noise
looking at barbed wire cattle fences. Did NOT spot any yellow
insulators, so I am leaning in favor of power lines.
73
Rick N6RK
On 1/2/2023 11:15 AM, Don Kirk wrote:
Hi Richard,
I tried sending this early today but my attachments appeared too big, so
here it is with reduced file size attachments.
I looked at your RFI audio recording with my oscilloscope connected
directly to the audio out on my computer. Using FFT on my scope the
predominant frequency component is indeed 120 Hz as you initially said.
I'm going to stick my neck out and post the following comments which
might turn out to be totally incorrect but please remember I'm
definitely in the camp that says it does not matter what device is
generating the RFI (I preach this all the time), what's important is to
first locate the property where the noise is originating and then you
can figure out what device is generating the RFI.
I looked at the actual waveform of your RFI recording in the time
domain, and assuming we are looking at power line RFI what I believe I'm
seeing is that at times there is an arc only 1 time per each half cycle
of the sine wave, sometimes 2 arcs per each half cycle of the sine wave,
and occasionally 3 arcs per each half cycle of the sine wave, and then
there are times (example 0.2 seconds) that there is no arcing at all.
In the past I used to do this kind of waveform analysis a lot but with
my improved DFing techniques and availability of SDR receivers I now
hardly ever revert to it because it really does not save me time (but
it's scientifically fun).
I have attached two pictures showing screen captures of my oscilloscope
looking at very brief sections of your RFI recording in which the yellow
trace is your RFI, and the blue trace is a 60 Hz sine wave that I fed
into the second channel of my scope so you could see the approximate
relationship in time between a 60 Hz sine wave and the arcing pattern.
Please understand my 60 Hz sine wave is not lined up perfectly but it
should still help you visualize what I believe the situation is.
Note: My technique looking at your recording is not perfect because the
bandwidth of the receivers filter as well as recording and playback
equipment is critical regarding frequency response and therefore what
you see, so take what I have said above with a big grain of salt.
Once again I'm pretty darn confident you are dealing with power line
noise and I would therefore pack AM VHF DF gear or at least have it
available at your house so once you get close to the source you can
switch to VHF from MF/HF in case it really does turn out to be power
line noise, but with a lot of attenuation and if out in the clear you
should be able to get very close to the suspect pole using HF.
73, and keep us posted on what you find assuming the RFI is still
present when you get your new DF hardware (sometimes even power line RFI
disappears over time).
Don (wd8dsb)
On Sat, Dec 31, 2022 at 5:18 PM Don Kirk <wd8dsb@gmail.com
<mailto:wd8dsb@gmail.com>> wrote:
Hi Richard,
Great recording.
Definitely does not sound like electric fence and I would initially
say it’s poweline noise (listening on my phone) and not a regular
pattern at all but when I get some free time in the next few days I
will use some software to look at it. Based on the sound and based
on it going away when it rains I would say poweline noise with very
high confidence but let’s see what other experts say. Should be
pretty darn easy to get very close to the suspect pole with the
portable flag before going to VHF to determine the actual pole if it
is power line noise, just stay away from overhead lines when
determining direction and attenuation is your friend. Even if it’s
not poweline noise you should be able to find that bad boy easily
because it’s not a constant noise (has variability to it which
really helps distinguish it from other sources of noise).
If possible look at the signal using a SDR display / pan adapter
before heading out to determine what bands and frequency you hear it
well, and this will be helpful to your decision making about what
frequency or frequencies to use while out DFing it.
73,
Don wd8dsb
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