[RFI] RFI from variable speed drive 1.1 miles away (very interesting case).

[Don Kirk]

Hi Mike (W9IP),

Are you able to see my youtube video as everything shown in my video is in
the frequency domain.  The top display is the RF spectrum display with a
waterfall of it right below, and then near the bottom of the screen is the
Audio spectrum display along with its waterfall below it.  Probably the
best display for you to look at would be the one starting at around 1:14 in
the video as it's displaying 1710 to 1900 KHz directly whereas the display
before it in the video is looking at the IF output of my HF rig so the
frequency probably makes no sense to you.  I also made some recordings
using my HDSDR software so I can go back and look at the captured signal as
if it were real time so I can zoom in or out for you if needed over a 2 MHz
wide slice of the spectrum I recorded.

Let me know what you need and I would be glad to provide it as long as I
have it available.

73,
Don (wd8dsb)

On Thu, Nov 17, 2022 at 7:50 AM <nlsa at nlsa.com> wrote:

> Dear Don -
> Could you post an image of what the interference looked like in the
> frequency domain?
> 73,
> W9IP
>
> -----Original Message-----
> From: RFI <rfi-bounces+nlsa=nlsa.com at contesting.com> On Behalf Of Don Kirk
> Sent: Tuesday, November 15, 2022 8:57 PM
> To: RFI <rfi at contesting.com>
> Subject: [RFI] RFI from variable speed drive 1.1 miles away (very
> interesting case).
>
> Today I tracked down new RFI at my QTH on 160 meters.  I was able to hear
> the RFI from my driveway using my portable flag with the DX Engineering
> preamp and it indicated the RFI was arriving from the SW (similar to what
> my
> stationary pennants indicated).  Using the portable flag I was able to
> quickly track the RFI down to a variable speed drive located at a Living
> Historical Museum located 1.1 miles from my house and it was pretty amazing
> how strong the signal was at my QTH considering the distance.
>
> This case was very interesting because the variable speed drive is for a
> fan
> that blows air into the bottom chamber of a 105 foot tall tethered Helium
> balloon that takes passengers to a height of 377 feet.  The air is blown
> into the bottom chamber of the Helium balloon to maintain a constant
> pressure in the balloon regardless of the outside temperature.
>
> I had never encountered this RFI before and it turns out their old variable
> speed drive system was recently replaced with a new variable speed drive
> system.  We replaced the new system with their old one and this stopped the
> RFI.  They will now follow up with the manufacturer of their system to
> investigate a solution, and I will help support their troubleshooting as
> needed and until then they will use their old system.  It does appear a 3
> phase powerline filter has been installed on the input of the variable
> speed
> drive on both their old and new systems.
>
> For those interested here is a link to a youtube video I just uploaded that
> documents this case.  https://youtu.be/Qnz4E9r5vj0
>
> Note: the more I use my portable flag which is unidirectional the more I
> appreciate how much time it saves me compared with my bidirectional tuned
> loops as I instantly know the direction the RFI is arriving.  It often
> saves
> me hours if not days locating the source of RFI.
>
> Just FYI and 73,
> Don (wd8dsb)
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