[RFI] Quidance on finding noise?

Thu Jan 9 19:08:58 EST 2020

Hi Jim,

Not sure who your question was directed to regarding syncing on the line
frequency.  I have done that before, and about a week and a half ago we
used this technique at WB9DKL on a power line arcing issue.

Don (wd8dsb).

On Thu, Jan 9, 2020 at 6:51 PM AA5CT <jwin95 at yahoo.com> wrote:

> One 'arc' strike per half cycle is visible (like a spark gap
> transmission), yet, not an arc.
>
> Have you ever seen an O-scope used this way? Synced to
> the line rate? To see the strikes per cycle?
>
> This matches the 'arcing' sources I've tracked down before.
>
> I had a real-time Spec An I could put in Zero Span mode and
> trigger from the "Line" and observe sometimes two or three
> strikes per 1/2 cycle on one noise source about 10 yrs back.
>
> One could also hear the change in 'tonal' quality as the strikes
> would sometimes be 2 and sometimes 3. This source turned
> out to be a primary wire to a fuse holder that had broken loose
> and was 'moving' (like bouncing) slightly in the wind. One
> could visually see the arc and I even managed to capture
> the arc in a still picture I included in a pdf file documenting
> that adventure too. Maybe it was more than a decade back?
>
> Too bad I don't have a video of the Spec An in Zero Span mode
> although I'll have to check an older PC to be sure. The nice
> thing about a Spec An with that capability is I could widen-up
> the IF bandwidth and the "strikes" would then sharpen-up and
> become quite distinct.
>
> de AA5CT
> .
> .
>
>
> On Thursday, January 9, 2020, 4:31:06 PM CST, Michael Martin <
> mike at rfiservices.com> wrote:
>
>
> Not an arcing source.
>
> Get BlueMail for Android <http://www.bluemail.me/r?b=15726>
> On Jan 9, 2020, at 3:39 PM, Don Kirk <wd8dsb at gmail.com> wrote:
>
> Hi Jim,
>
> I looked at that RFI noise in sync with 60 hertz video you wanted me to
> look at using my soundcard scope, and attached is what I captured.  Very
> obvious 120 hertz.
>
> I also just took another look at Kens audio recording using another
> recording he supplied me which gave me more time to listen without human
> voice on top of the noise, and I do in fact see 120 hertz bursts (not 60 as
> I initially reported), but not narrow bursts like the recording you had me
> look at.
>
> Either way I believe the info we have supplied Ken should help him track
> down the source.
>
> Thanks,
> Don (wd8dsb)
>
> On Thu, Jan 9, 2020 at 12:43 PM AA5CT <jwin95 at yahoo.com> wrote:
>
> Don,
>
> Can you feed this video's audio into the analysis software and
> see what it gives? As can be clearly seen there is a 'pulse' for
> each 1/2 cycle of the AC waveform, or two pulses for a complete
> cycle of 60 Hz mains.
>
>
> https://www.youtube.com/watch?v=C-S5ef-Ne6Y
>
>
> Also note that the first 'breakdown' shifts around, while the second
> breakdown is fairly constant; this is due to materials or the structure
> involved in the area of where the arc forms.
>
>
> Note: Scope triggered from local "Line" voltage, also shown overlaid
> as a single cycle as seen on the scope's CRT.
>
>
> de AA5CT
>
> .
> .
>
> On Thursday, January 9, 2020, 10:46:02 AM CST, Don Kirk <wd8dsb at gmail.com>
> wrote:
>
>
> Hi Ken,
>
> Using 3 different audio software tools, I come up with a frequency of 60
> Hertz, not 120 Hertz. Typically power line noise has bursts at a frequency
> of 120 hertz (arcing each half of the sine wave).
>
> If it really is not power line noise which I suspect it's not, you will
> probably have a somewhat easier time locating it. It appears you have a
> good idea what direction it's coming from assuming the gain of the
> beverages are similar to each other. If so I would say the noise is from
> the East North East. If it were me I would use a portable tuned loop with
> portable preamp and portable HF receiver that would allow me to hear the
> noise just outside the house of KC4D, and then I would use the null (or
> peak) of the tuned loop to guide me right to the source while heading in
> the East North East direction (I consider this method a form of infinite
> triangulation because as you walk you continue to use the null of the loop
> to guide your direction of travel), I would reduce receiver gain or install
> attenuation as I get closer to the source so that I could still detect the
> null as I rotate the loop. In my experience you should be able to narrow
> in on this noise within 15 to 30 minutes of walking. Most folks probably
> are not willing to invest in a preamp (buying or building one).
>
> The problem is that overhead power lines can radiate the signal, so you
> need to stay away from the power lines as much as possible. When this is
> the case, I then do true triangulation by going to different locations away
> from power lines to get headings, and then I plot the headings on Google
> Earth to see where they intersect.
>
> You should probably be able to hear this noise with a portable AM broadcast
> band radio too, and you might be able to just use the built in loop stick
> antenna to guide you to the source (using the null and peak method) but if
> you can't throw in attenuation as you get close you might have some
> difficulty when you get very close to the source, but I would certainly try
> this method. When you get right next to the source you might be able to
> hear it up on 136 MHz AM (if you have a police scanner this would be a tool
> you might try as the aviation band on the radio will provide AM reception),
> but this is probably not even necessary but might be very helpful in
> confirming you have located the source.
>
> If you want to assume it could be a street light (I see a lot of street
> lights on the main roads near KC4D), and you know the approximate time the
> noise shows up each day, I would listen on my cars AM radio while parked
> out on the side of these roads to see if I could catch the noise coming on
> when the lights turn on (observing both street lights and house lights,
> etc.). This assumes you are able hear the noise (a lot of new car radios
> have such good noise blankers that you can't hear this type of noise).
>
> There are a lot of other tools I use such as portable SDR receiver, but
> again that's normally more than most folks want to mess with for a one time
> situation.
>
> I would recommend driving the streets up to an approximate 1 mile radius
> and note the noise level during the day and during the night, and note
> where the noise was horrible at night but not during the day (this might be
> the very first thing I would try to do to isolate the problem while keeping
> things simple for you).
>
> Everyone has their own technique, and you need to work with whatever tools
> you can easily obtain.
>
> Keep us posted.
>
> Don (wd8dsb)
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