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

[Dave Cole (NK7Z)]

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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