Please let us know what the outcome is.
richard
On Fri, Feb 2, 2018 at 7:28 PM, Don Kirk <wd8dsb@gmail.com> wrote:
> Hi Cortland,
>
> Thanks for the info. I just constructed a 3" diameter loop (not tuned)
> using some pretty rigid RG58U, and will try it along with a 6" diameter
> tuned loop (adjustable between 20 and 30 MHz). I have basically tracked
> the RFI down to a room, but the room is packed full of motor controls
> (numerous VFDs, etc.). The 3" diameter loop appears to be working well
> with my SDR receiver based on some simple bench top testing I just did.
>
> Thanks,
> Don (wd8dsb)
>
> On Fri, Feb 2, 2018 at 4:00 PM, Cortland Richmond <ka5s@earthlink.net>
> wrote:
>
> > Hi, gents. Cortland here, KA5S.
> >
> > I had about a 30 year career in EMC engineering, and often had to locate
> > specific sources of EMI.
> >
> > A quite small loop will do very well if one is in close proximity to the
> > magnetic field of an emitter. That is, there is a good deal of utility
> in
> > entering the near field very closely.
> >
> > You may remember the famous 3520 kHz television modems of some years ago.
> > For those I tried using three antennas; a surplus EMC loop antenna about
> 1
> > m in diameter, ad un-tuned whip antenna, and about a 3 inch loop antenna
> > made by bending a piece of semi-rigid cable back on itself and soldering
> > the exposed center conductor at the non-connectorized end to the outside
> > of the shield near the connector.
> >
> > This last was unbalanced, but its small wavelength aperture made it good
> > almost through VHF.
> >
> > At 80M, on a handheld receiver, it could accurately lead me to the exact
> > room one of those modems was radiating from.
> >
> > Much smaller loops can be constructed on the open end of a single piece
> of
> > coax, and can follow individual traces on a PWB – but that is beyond the
> > scope of this discussion.
> >
> > Good luck!
> > Cortland
> > ka5s
> >
> >
> > On 2/2/18 2:32 PM, Don Kirk wrote:
> >
> >> Hi Dave and gang,
> >>
> >> I totally agree on the smaller loop, but I believe what is also
> important
> >> is to factor in the implications of being in the near field. That's
> why I
> >> think going to a much higher frequency would be very beneficial (get out
> >> of
> >> the near field as much as possible, but we will see).
> >>
> >> Stay tuned (no pun intended).
> >>
> >> Don (wd8dsb)
> >>
> >> On Fri, Feb 2, 2018 at 1:51 PM, Dave Cole (NK7Z) <dave@nk7z.net> wrote:
> >>
> >> I would try a a much smaller mag loop, like a foot in diameter. I have
> >>> used a 6 inch loop in some cases, they are still sort of directional.
> >>> Add a
> >>> ferrite on the coax at the feed point. I have one loop that is about
> an
> >>> inch in diameter, I use it seldom, but it is handy when needed.
> >>>
> >>> I also have a small probe I built out of a piece of coax, I just cut
> the
> >>> shield back 3 inches, used dollop of liquid electrical tape on the end
> of
> >>> the center conductor for insulation, and then I probe around...
> >>>
> >>> 73s and thanks,
> >>> Dave
> >>> NK7Z
> >>> http://www.nk7z.net
> >>>
> >>> On 02/02/2018 10:20 AM, Don Kirk wrote:
> >>>
> >>> Quick follow up on my locating the source of the repeating 15 KHz
> >>>> signal
> >>>> (actually 15.6 KHz).
> >>>>
> >>>> Today I met with the suspect facilities machine controls engineer that
> >>>> just
> >>>> happens to be an inactive but still licensed ham (turns out we also
> have
> >>>> mutual friends in the machine controls world).
> >>>>
> >>>> I first walked around the entire perimeter of the building (outside in
> >>>> very
> >>>> cold temperatures) using my portable SDR system, and was able to
> >>>> determine
> >>>> that the source of the interference is located near the west central
> >>>> part
> >>>> of the building where there are several water cooling towers as well
> as
> >>>> material storage silos. The signal is indeed cyclic but still need to
> >>>> see
> >>>> how repeatable the cycle is (typically on for about 20 minutes and
> then
> >>>> off
> >>>> for about 20 minutes). Inside the west wall there are a bunch of
> >>>> facilities related equipment (pumps, variable speed drives, etc.).
> >>>> Unfortunately my 160 meter tuned loop is useless when in so close to
> the
> >>>> source, and we were not able to determine the actual source in the
> >>>> allotted
> >>>> time we had today. With the SDR receiver gain set at 0, the signal
> was
> >>>> still near full scale when in close to the source (it appears we have
> >>>> the
> >>>> source nailed down to about a 50 foot by 25 foot area, but there is a
> >>>> ton
> >>>> of motor controls equipment in this small area as well as metal
> building
> >>>> structure that likely is confounding our DFing).
> >>>>
> >>>> We are now going provide my vehicle description, name, etc. to the
> >>>> security
> >>>> department that patrols the grounds of this facility so they know I
> have
> >>>> permission to be on the property 24 hours a day 7 days a week. I'm
> >>>> going
> >>>> to obtain more data on the cyclic nature of the interference (to see
> if
> >>>> it
> >>>> provides any clues), and also evaluate capturing the signal at much
> >>>> higher
> >>>> frequencies (determine what the highest frequency is that I can still
> >>>> capture the signal), and then build a DF antenna for the higher
> >>>> frequency
> >>>> to help pinpoint the source when in close. After I obtain more data
> >>>> from
> >>>> outside the building and develop a better antenna for in close DFing,
> I
> >>>> will then go back into the building to continue our in close DFing (as
> >>>> time
> >>>> permits).
> >>>>
> >>>> My portable SDR system consists of a Dell laptop, NooElec SDR dongle,
> >>>> and
> >>>> ham it up converter (stuck to the back of the laptop screen using
> double
> >>>> stick tape). The SDR dongle and ham it up converter are powered via
> the
> >>>> laptop USB ports which makes it very convenient. I just plug my DF
> >>>> antenna
> >>>> into the ham it up converter and adjust the SDR dongle gain as needed
> >>>> (via
> >>>> the SDRSharp software I'm using).
> >>>>
> >>>> Just FYI,
> >>>> Don (wd8dsb)
> >>>>
> >>>> On Mon, Jan 22, 2018 at 9:15 AM, Don Kirk <wd8dsb@gmail.com> wrote:
> >>>>
> >>>> Yesterday I tracked down RFI that has been bothering me on 160 meters
> >>>> for
> >>>>
> >>>>> the past year. The source was a little hard to find because it's not
> >>>>> always on. I finally had to use my SDR dongle with Ham it up
> converter
> >>>>> in
> >>>>> the car with my small tuned loop to track down the source of the
> >>>>> interference (in order to make sure what I was seeing at home was
> what
> >>>>> I
> >>>>> was actually tracking). The suspect source is 0.75 miles from my
> >>>>> house.
> >>>>> Here is a link to a video showing my efforts to date.
> >>>>>
> >>>>> http://www.youtube.com/watch?v=LKf1EWTV8xs
> >>>>>
> >>>>> Today I will contact the manufacturing facility that I tracked the
> RFI
> >>>>> down to in order to take the next step with them.
> >>>>>
> >>>>> I will report the actual source of the RFI as soon as it's determined
> >>>>> which might take some time (usually takes time to establish a good
> >>>>> working
> >>>>> relationship with the suspect property owner). Based on past
> >>>>> experience
> >>>>> it
> >>>>> sure looks like a variable speed drive, but in order to keep an open
> >>>>> mind I
> >>>>> try not to guess ahead of time.
> >>>>>
> >>>>> Just FYI,
> >>>>> Don (wd8dsb)
> >>>>>
> >>>>> _______________________________________________
> >>>>>
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> >>>>
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> >>>
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> >>
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