How to do spectrum analysis of AC line noise.

[BryanSw]

I need to do a spectrum analysis of AC line noise. I am not sure what type of equipment to use to perform these measurements.

Problem I am having is I have line noise coming from my power lines into my house. This noise is very noticeable on ham radio equipment , as well as cb radio, and stereo equipment. The noise seems to be repeating at every 30khz interval. Can I perform this analysis using Labview and some constructed circuits along with my NI data acquisition card which is a PCI-6040. The Pci-6040 can do 500 kS/s for a single channel. I want to be able to present the measurements to the power company. They already came to my property but would not do anything even after I verified that the problem is on their end by having them pull my meter from the house. I then turned on a radio outside the house and stood by the power lines and still had very strong noise interference coming from the power lines. I don't want to spend the money on a spectrum Analyzer just to do a test so I was thinking Labview might be able to do this with my Daq card. Could it be done?

Thanks, any help is greatly appreciated.

[johnsold]

First, the power company has an obligation to alleviate harmful interference to liscensed radio communications systems.  The ARRL has an active interference program. If you are not making progress with the power company directly, ask the ARRL for help.

Next, it can be very difficult to find the source of the interference. I once spent several days running all over a small city with a power company engineer with oscilloscopes and spectrum analyzers looking for the source of an interfering signal which affected measurements made by the largest employer in the city. We never did find the source.

Be very careful with any measurements you make from power lines. An incorrect connection can kill or injure you or damage or destroy your DAQ equipment and computer.  As a ham radio operator, you probably know this, but others reading the Forum might not.

As a starting point I suggest using a 6 V filament transformer (or lower voltage - whatever your junk box has). Connect the low voltage secondary to the DAQ inputs. A resistor which draws tens of milliamperes or more (watch power rating) to load the transformer might be a good idea. The transformer high frequency response may not be all that good but you may be able to see a 30 kHz signal.  Sample at the highest rate possible.  Your DAQ device only has 12 bit resolution.  This will limit the dynamic range.  If you do not see anything, or see something but it is very small compared to the 60 Hz component, 

then a simple RC high pass filter which passes 30 kHz but suppresses 60 Hz might help.

Please post any data you collect and I will take a look at it.

Lynn

WA8MGI, MSEE, P.E.