[RFI] Noise Canceller vs DSP filter
EDWARDS, EDDIE J
Mon, 21 Oct 2002 15:23:57 -0500
From: Rob Atkinson, K5UJ
The lower you go in frequency the less the distance between your ant.
the lines has a preventive effect. Also, at lower frequencies, you
rxing noise standing waves on the power lines.
What Rob is describing is the fact that the noise at the lower freqs can
be directly picked up at much greater distances than the noise at higher
freqs. This is why it's generally better to use VHF (140-200Mhz) when
searching for the source. There's a great graphic of this in William
Nelson's "Interference Handbook on pg 58.
Also, I've found that noise transmission standing waves occur pretty
much across the spectrum. It's just easier to hear standing waves at
lower freqs due to larger amplitudes when noise is propagated this way
(as opposed to direct radiation). When listening at VHF try changing
the polarity of your antenna. Easier to do when carrying a yagi around
then when using your car's antenna. There's a good diagram of standing
waves shown in Nelson's book on pg 104.
I'm getting periodic bursts of line noise now--when it's on it consists
burst of a few seconds with about 20 seconds of silence. I'm thinking a
neighbor has an electric blanket or fish tank heater turned
controlled by a thermostat. Can't think of any other possibilities. It
hasn't been real bad so I'm living with it for now.
I had this same problem when a neighbor installed one of those
electronic fences for his dog. The dog's collar mildly shocks the dog
when he gets too close to the perimeter where a wire has been buried (or
in my case, hung on the fence to keep the dog from jumping the fence).
It sends periodic pulses everytime the dog gets close to the edge of the
Saw this system fail to keep a dog in the yard once while riding my
bicycle. The dog took off after me from the deck/porch. When it hit
the "no-go" zone I heard it "yelp". I looked back in time to see it
falling and rolling on the ground (near the perimeter?), then getting
back and coming after me--this time clear of the perimeter!!! Yikes!
Did I ever pedal like hell.
My pulses ended when the neighbor moved away taking his wireless fence
de ed -K0iL