[RFI] Overnight interference

Dave Cole dave at nk7z.net
Mon Jul 25 01:02:58 EDT 2016

On Sun, 2016-07-24 at 20:40 -0700, KD7JYK DM09 wrote:
> Listened to your recording.  I hear a hum, but don't see anything at
> 60 Hz.  I do see consistent traces at 240 Hz.  As for your thought of
> data, I don't see any patterns, but there is an odd data burst that
> can be heard around 15 seconds, maybe something else on the frequency
> you were monitoring?  I did a spectrogram of the noise, it's
> intentionally formed to be within the "voice" range of a telephone or
> radio.  Are you using some sort of filters in your receiver?
> Generally, the noise sounds like a light on a pole I watched as it
> turned on and off and produced similar noise as well as a
> malfunctioning LED street lamp.  These were both limited in frequency
> range by their physical characteristics, that is to say, for example,
> noise from 1-4 MHz.

I am pretty sure that data burst is carried with teh RFI...  It's timing
seems almost perfect.  Also, new data as of tonight, the start/stop
times are to the second day to day, over two days.  I will hope that it
is shortening a bit each day, that will point to something solar in

I suspect you are seeing the K3 audio and RF filtering roll things off.
I have the widest filter I have for AM on, which is 5 KHz.

I have an SDR I will be bringing out on this so I can make sure I am
nulling the right signal with the loop once I get to that stage.

The most fascinating thing is that the signal rolls off some 15 db,
between 1.750, and 1.700, and is gone by 1.600 MHz.  Awfully steep to be
by accident in my mind.  I have seen this before in a Ethernet over
power line adapter.  A friend needed some DFing of a broadband source,
done for his SWLing, each ham band was rolled off like that too.

I will report what I find once I get a part for my mobile antenna.  It
should be here tomorrow...  I will spiral out, already have my maps made

73's, and thanks,
Dave (NK7Z)
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