630 Meter Interference

I had a chance tonight to examine the interference that is blocking reception of the 630 meter band in the evening.  Last night the interference stopped abruptly around 11:15pm local time.  As I suspected the noise returned tonight.  I was out when it started but it was in full force when I returned at 7:30pm.  This gave me a chance to examine the noise in more detail.  First was to look at the audio coming from the receiver.  What this shows is a series of pulses space approximately 8.2 ms apart.  The inverse of this is the frequency which is around 120 hz.  That is why I hear the low frequency buzz in this interference.  I have observed a similar pattern with arching of high voltage distribution hardware.  In that case the noise was very broad band.  Covering from HF into UHF.  In this case the noise is limited to a much narrower bandwidth.  Considering the bandwidth and the way it shuts off I am sure this is a device and not power line hardware related. 

 

Looking at the FFT signature of this same audio sample I see a square pulse that starts around 115 hz and ends around  3.488 KHz.  I think that is why, on Spectrum Lab, I see flat audio response out of the receiver for its full 3100 Hz bandwidth.  The FFT image is shown below:

Looking at a spectrum analyzer from 410 KHz to 500 KHz I see the following.  This essentially wipes out the 630 meter band. 

It will be interesting to find out what this is.  I suspect this is a television or something in the room with a television that household turns on in the evening and turns it off when they go to bed.  So far I have not heard this noise during the day (Monday - Friday). 

To track this down I plan on taking a ferrite rod and build a loop stick antenna. Those have a sharp null off of the end of the rod.  Walking around the neighborhood I hope to be able to use that null to at least locate the house where it is coming from.   Of course I need to make sure it is not something within my own home.  That would be an easy fix if that was the case.  Since this shut down last night around 11:15pm I can not think of anything in the house that would have done that last night.