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@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@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@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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--
*Dave - WØLEV*
*Just Let Darwin Work*
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