This is good advice, as you might expect from a professional, which Mike
is. With my 18 MHz portable SW receiver I can walk down the line and hear
distinct peaks and valleys. Often, at that frequency, I can hear the peaks
increase as I walk toward the source and decrease as I walk away. Once I
get close, I switch to a 136 MHz AM handi-talki with a Moxon antenna for
the last little bit of zeroing-in. Speaking of which, it's a beautiful
afternoon and one of my noises is back - time to go hunting.
73, Pete N4ZR
At 11:50 AM 10/12/2008, RFI Services wrote:
>Hey guys,
>
>Experience in listening is the best tool for identifying power line sources
>verses other types including in-house arcing sources. A good scope helps as
>well.
>Here is some additional info that may help.
>
>Arcing sources of all types, as previously mentioned by almost everyone, are
>broad and that characteristic helps to identify itself. The fact is they
>will radiate in the range from below 1 meg to above 2 gig. The frequency
>range of an arcing noise source (noise) is determined by the frequency range
>of the antenna being used and signal strength of the noise from the
>receiving antennas position.
>I really don't want to write a book but would like to clarify a few things.
>
>If you're using an antenna tuned perfectly at 7 meg and the distance between
>your antenna and the noise source is a distance of exact wavelengths for 7
>meg, your signal for that noise will be peaked at 7 meg and will be at its
>highest level at that frequency. If you move that 7 meg antenna at less than
>1 wavelength increments the signal level will be lower than what it would be
>if positioned at the peak of the wavelength. To make this simple, let's use
>145 meg. We're parked on the street and receiving noise at 145 meg using a
>1/4 wave antenna tuned for 145. We reduce our gain to a minimal signal level
>and move the vehicle. We'll be able to see the signal level rise and fall
>every 2 meters. If you find the vehicles physical position where you're
>receiving the highest signal level, reduce your gain and then mark your tire
>position on the street, then roll forward to the next peak and mark it you
>can measure 2 meters between the marks. If you change the receiving
>frequency the marks will change to the wave length of that frequency. This
>is an example I use during my field classes. This same explanation is why
>you'll receive a power line noise stronger on one antenna than received on a
>different one of the same band or not. If you were to move the tower holding
>the antenna you could increase or decrease the signal level of the noise. I
>once had an RFI complainant in CA that I had explained this to. I received a
>call from him at 11:00 pm explaining that he figured he had enough space in
>his yard to move his tower out of the peak of the noise signal. I told him
>he was a genius. However, What is the chance you'll be moving it to a
>location that receives noise from other source(s)? Let's just fix the
>original source.
>
>While listening to your noise, for example at 7 meg, using AM mode, you
>change your frequency and the sound of the noise changes with the different
>frequency, it isn't power line noise. If the noise stops due to the small
>change in frequency, it's not power line. You should receive your power line
>noise throughout the receiving range of the antenna. You may see the noise
>signal peak and fall with the antenna resonance but you shouldn't see it cut
>of more rapidly than that. Using a spectrum analyzer (not a recommended
>locating tool) you can see the antenna's bandwidth and strongest resonance
>if receiving an arcing source. If it's a non arcing source you'll see the
>narrow signal and possibly the harmonics. Power line noise doesn't create
>harmonics.
>
>Most inside arcing sources, when the audio is monitored using an
>oscilloscope, appear more dense than power line sources and usually have a
>timely and sharper start and stop signature.
>
>It isn't likely you need to concern yourself with corona or flashover. These
>terms are used allot and are almost never an amateur radio problem.
>
>As for the hf spectrum, the power line noise will affect the range of your
>antenna which is also affected by the strength of the signal.
>
>A couple of good books on the subject are:
>AC Power Interference handbook by Marv Loftness or anything written by him.
>The ARRL RFI Handbook. Both available through the ARRL
>
>I'm sorry for the lengthy input, you should have seen it before I read it
>the second time.
>
>Mike Martin
>RFI Services
>6469 Old Solomons Island Rd
>Tracys Landing, MD 20779
>rfiservices.com
>240-508-3760
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|