I've not reported on this issue in a long time, but finally making progress
with interference that's originating from an apartment complex 0.4 miles
away. Back on Dec 11, 2014 we (myself and the apartment complex
maintenance manager) tracked the problem down to the variable speed drives
that are part of their "kitchen air makeup system". In this system there
are two drives that operate together, with one being a 3 HP drive for the
kitchen hood exhaust fan, and the other is a 5 HP drive for air makeup.
Here is a link to a video I uploaded onto youtube that captures the
interference when the drives start up (really an interesting video using an
RTL-SDR receiver and upconveter). http://youtu.be/LIWd2Dd-Fa0
On Jan 30th of this year I made a list of recommendations, with the
understanding that the apartment complex and their suppliers were fully
responsible for any changes made to their system (I assumed no liability
for their actions to mitigate the interference). After a long period of
time and no action, I called the FCC (March 3rd) and was told I should file
an official online complaint with the FCC which would then initiate action
by the FCC enforcement division. I passed this info onto the apartment
complex regional maintenance manager, and that is when things started to
move forward. The out of state firm that designed the "kitchen air makeup
system" hired a local mechanical/electrical firm to work on the problem,
and the local technician has been very proactive.
3 weeks ago input line filters manufactured by the variable speed drive
manufacturer were installed on both drives, and this definitely reduced the
level of interference. Start up peaks spaced 4 khz apart were originally
15 dB above my noise floor and after installation of the input line filters
they are now 5 dB above my noise floor. The very broad band white noise
that develops a short time after start up is now very hard to detect
whereas it was previously 4 to 6 dB above my noise floor.
The local technician is now planning on additional changes since the input
line filters have not totally mitigated the problem (but they sure helped),
and will provide an update when I have new information to share.
For more in depth details see my website that's documenting this case
http://sites.google.com/site/broadbandrfi/
73,
Don (wd8dsb)
On Fri, Oct 24, 2014 at 2:40 PM, Don Kirk <wd8dsb@gmail.com> wrote:
> Recently noticed an increase in my noise level on 160 meters (in the
> direction of my 300 degree pointed pennant), and about 3 weeks ago I
> tracked it down to a new apartment complex which is located 0.41 miles
> away. Today I noticed that the signal had a repeating pattern of
> approximately 30 minutes on and 5 minutes off when listening at my house,
> so I jumped in the car and drove over to the apartment complex to make sure
> the signal at the apartment complex had the same repeating pattern and was
> in time sync with the noise at my house. Thankfully it was, and I made
> recordings at the apartment complex today showing I could predict when the
> signal would go off and come back on based on the time pattern I was
> following at my house.
>
> I have created a website documenting my direction finding activities for
> this broadband RFI case, and uploaded my prediction recording today. Here
> is the link to my simple website that documents this case :
> http://sites.google.com/site/broadbandrfi/
>
> I contacted the apartment complex today notifying them that I was now 100%
> confident that the broadband noise was originating from their building, and
> will now work with their management to locate the exact source so they can
> follow up with the manufacturer of the equipment for resolution. Based on
> what I have heard so far it sounds like a motor (probably a variable speed
> motor controller), but that's just a guess at this time (sounds like it's
> winding up in speed when it first comes on and you can hear this on the
> recording I made at the apartment complex today).
>
> Just FYI, and another very interesting one to track down.
>
> 73,
> Don Kirk (wd8dsb)
>
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