[RFI] RFI every 15 KHz on 160 meters, suspect source is a manufacturing facility.

Cortland Richmond ka5s at earthlink.net
Mon Feb 5 15:48:36 EST 2018 

And even if each WERE FCC Class A compliant, together, they could  -- 
switching synchronously -- far exceed the limit. A cheap switcher might 
lock to noise on a common power source, whether generated elsewhere or 
on one or more switchers.


Cortland
KA5S




On 2/5/18 12:09 PM, Hare, Ed W1RFI wrote:
> That system would be a Class A Part-15 device, so would have to meet the higher industrial limits. Locally, ie near the motors, controller or wiring, I could well imagine a 50+ dB increase in noise from a "legal" device.  If that were 55 dB at a nearby Amateur antenna, it is possible that the system exceeded the Class A limits.
>
> Ed, W1RFI
>
>
>
> -----Original Message-----
> From: RFI [mailto:rfi-bounces at contesting.com] On Behalf Of David Eckhardt
> Sent: Saturday, February 03, 2018 12:50 PM
> To: Cortland Richmond
> Cc: RFI
> Subject: Re: [RFI] RFI every 15 KHz on 160 meters, suspect source is a manufacturing facility.
>
> 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 at earthlink.net>
> wrote:
>
>> 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 at 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 at 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 at 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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