Topband: lift station noise

[Jim Brown]

On Tue, 7 Apr 2009 15:24:57 -0400, Larry Pasman wrote:

>I am having a problem with a noisy sewage lift station near my QTH. 
>When trying to work 160 DX early mornings I will hear a "pop" then 
>nothing but hash until the lift station shuts off with another "pop". 
>Of course during the morning hours people are getting ready for work, 
>school and such so the lift station comes on frequently. Any ideas 
>how to approach this.

Not an easy solution, Larry. On YOUR end, you might be able to kill it 
by putting it in the null of a directional RX antenna, but that won't 
help for DX coming from the same direction. :)  

The root cause of the problem is probably a noisy controller for a 
motor associated with that system. These controllers work by first 
rectifying the power line to create DC, then chopping it and using the 
chopped waveform to drive the motor. Speed is controlled by varying 
pulse widths. That chopping creates strong harmonic content in the 
current waveform. The stepdown transformer, the motor controller, and 
the motor are often widely separated from each other (to make life 
easier for the electrical contractor), and there are bypass capacitors 
on the controller and leakage capacitance to ground at both the 
transformer and the motor. All of this combines to form a current loop 
for that HF noise, which in turn creates a big magnetic field. 

Problems like this are most effectively solved at the source, but that 
means you must get the noise polluter motivated to do so. That's 
probably not easy. If I were the engineer responsible, I'd first 
contact the mfr of the controller and try to get a noise-reduction 
modification for it. That would most likely involve slowing down the 
rise time of the control pulses -- the strength of harmonics is 
approximately proportional to the rise time. 

73,

Jim Brown K9YC