[RFI] Powerline noise question

[Richard (Rick) Karlquist]

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 at gmail.com 
> <mailto:wd8dsb at 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
> 
> 
>