Leigh L. Klotz, Jr. wrote:
> I have a buzz that happens some, but not all, nights, and not during the
> day, at least so far.
> On HF, I can hear it 80-20; I haven't tested other bands.
>
> Here is a screenshot of what it looks like in an SSB receiver:
> http://wa5znu.org/2007/10/rfi/rfi.png
>
> The axes are in ms, and the period is close enough to 120Hz that I think
> that's what it is.
>
> Here's what I've done so far:
>
> 1. Rotated a 20m beam and found the general direction, with about a 35
> degree beamwidth.
> 2. Used a simple wire loop on a TH-F6a set for AM on ~5Mhz and found
> it's not coming from my house.
> 3. Found a strong buzz coming from the sodium vapor light in front of my
> house, but it could also be just coupling from the light mast as an
> antenna (same effect for WWV on 5 MHz).
> 4. There is no correlation between the sodium vapor light being on or not.
> 5. I haven't heard it during the day.
> 6. I haven't heard it every night.
> 7. There are other power lines around in the general direction.
> 8. I've been able to hear it from the light mast on 135Mhz but the wire
> loop isn't sensitive enough to find it at a distance; I will probably
> make a wire yagi if I need to do more looking.
>
> So, does this look like power line noise? Or should I be looking for
> something in a neighbor's house that they use at night that also somehow
> emits broadband noise with a 120Hz period?
>
> 73,
> Leigh/WA5ZNU
>
>
>
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>
>
Here is a link to QST about an easy to build yagi used in conjunction
with an MFJ 852 line noise meter.
http://www.arrl.org/qst/2007/05/HANSON.pdf
I have built and used successfully this system. I built into the metal
box enclosed MFJ 852 a 40 db pad. When you get close you need to reduce
the sensitivity of the receiver. I used RCA pin plugs to attach the
antenna to the MFJ. The input to the 40 db pad is mounted on the side of
the box.
The MFJ operates at 135 mhz and the antenna is right on frequency. In
use you may find that the offending source of rfi is sending it down the
line to the next pole(s). By using the 40 db pad and standing equal
distance from the poles you can tell which pole is generating the rfi.
The April 2006 issue of QST has an article by Jim Hanson on building a
ultrasonic line arc detector. It uses an 18" parabolic dish from Edmond
Scientific. This will take you to the next level in finding power line
rfi. Once you narrow the rfi down to a pole or two, the ultrasonic
detector will detect the location of the actual arc. A good source of
power line noise info is available at http://www.rfiservices.com/
Good hunting,
Smith Bradford
W9HAK
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