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Re: [RFI] RFI every 15 KHz on 160 meters, suspect source is a manufactur

To: Cortland Richmond <ka5s@earthlink.net>
Subject: Re: [RFI] RFI every 15 KHz on 160 meters, suspect source is a manufacturing facility.
From: David Eckhardt <davearea51a@gmail.com>
Date: Sat, 3 Feb 2018 17:50:27 +0000
List-post: <mailto:rfi@contesting.com>
Look for AC/AC or AC/DC switching converters.  I won't relate the story,
but we had an incident where 208/3-phase was fed to several speed
controllers on a large irrigation system (20-housepower AC motors).  The
proper and required decoupling components were not bought and installed due
to cost.  We experienced switching noises some 55 dB over baseline on a
portable R&S spectrum analyzer.  Our emissions peaked right in the middle
of the 40-meter band but were detectable to low VHF.  The controllers were
from China with a storefront on the west coast - what else is new these
days with no FCC enforcement.

Dave - WØLEV

On Sat, Feb 3, 2018 at 3:36 AM, Cortland Richmond <ka5s@earthlink.net>

> Great Don.
> On 2/2/18 8:28 PM, Don Kirk 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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*Dave - WØLEV*
*Just Let Darwin Work*
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