[RFI] Power line Bandwidth Characteristics

[Pete Smith]

Turned out to be on the pole that feeds my house - telephoning the power 
company tomorrow.


73, Pete

At 08:27 PM 10/12/2008, RFI Services wrote:
>Sounds like open season at Pete's. Rutt must have been early.
>
>Mike Martin
>RFI Services
>6469 Old Solomons Island Rd
>Tracys Landing, MD 20779
>rfiservices.com
>240-508-3760
>
>
>-----Original Message-----
>From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com] On
>Behalf Of Pete Smith
>Sent: Sunday, October 12, 2008 12:32 PM
>To: rfi at contesting.com
>Subject: Re: [RFI] Power line Bandwidth Characteristics
>
>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
>
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