Hi Paul,
You would helpful a step attenuator, in 1 dB steps, to be a valuable addition
to your tool bag. There are situations where it helps isolate to an individual
pole. Its much more accurate than an S-meter.
Something like this, or many other alternatives:
http://www.ebay.com/itm/Coaxial-RF-Step-Attenuator-Set-1-dB-steps-to-70-dB-total-DC-to-1-GHz-/200866468929?pt=LH_DefaultDomain_0&hash=item2ec4931441
73
Frank
W3LPL
---- Original message ----
>Date: Sat, 05 Jan 2013 11:44:08 -0500
>From: N1BUG <paul@n1bug.com>
>Subject: Topband: Another take on power line noise hunting
>To: Topband <topband@contesting.com>
>
>I've been following this discussion with interest. I spent the
>summer tracking down more than 20 sources of power line noise. As an
>offshoot of that I've made it my mission to help clean up RFI in my
>little corner of the world. I've been slowly drifting away from
>DXing and this has turned out to be my new area of interest.
>
>Since this topic is perhaps of interest to topbanders, and since my
>experiences seem to vary somewhat from the typical reported here so
>far, I thought I would take a moment to share some observations. I
>should probably note I was dealing with a mix of 13.2 kV
>distribution lines and 46 kV transmission lines. My hunt was made
>more challenging by the fact I had multiple sources in a relatively
>small area and could often hear more than one at a time even with
>directional antennas and attenuation.
>
>My tools this summer were 135 MHz AM receiver with 3 element yagi
>and step attenuator; LF/MF/HF/VHF/UHF AM receiver with DF loops for
>low bands and 7 element yagi for 445 MHz; ultrasonic receiver with dish.
>
>Low frequencies, eg. AM BC or 160 meters were *occasionally* useful
>in locating a general source area. Sometimes the area identified
>turned out to be an area of *radiation* but the noise was
>*generated* elsewhere. Often the relatively close proximity of
>multiple sources made low frequency tracking useless.
>
>VHF was always useful in finding a source area, 80% of the time
>resolving it to a single pole. The sharp, deep null at exactly 90
>degrees off axis of the yagi proved very useful for confirming a
>source structure. Poor resolution/accuracy of signal strength
>metering was perceived as a problem.
>
>UHF was very helpful in a few areas where the noise was particularly
>strong at VHF and/or signal strength so close over a span of several
>poles that VHF could not pick the source pole with high confidence.
>So far, experience indicates this is more likely to happen on the
>transmission lines. They're a bear. Again, poor or no signal
>strength metering (signal below AGC threshold) was perceived as a
>problem.
>
>The first ultrasonic unit tried was a waste, finding something at
>only 10% of RF noisy poles. The second unit was able to hear
>something from about 60% of the same 21 poles. The figures are
>averages over more than 10 runs with each unit. The two were also
>tested on a spark signal range under somewhat controlled conditions.
>These things are definitely not created equal!
>
>To date I have identified and had the power company fix almost
>everything I have worked on. The remaining open case involves a
>short section of a 46 kV transmission line which is extremely
>perplexing due to the specific nature of the issue (details on
>request). Just when I starting thinking I was getting good at this,
>I came up against this one.
>
>If I were doing this strictly for myself these tools would be more
>than adequate. Since I'm not and I only have so many hours in a day
>I have several upgrades on my wish list:
>
>HF/VHF/UHF AM receiver with wider bandwidth better signal strength
>metering
>
>Log periodic dipole array covering ~100 to ~900 MHz for frequency
>agility while maintaining some directional properties
>
>Portable oscilloscope for observing noise signatures in the field
>(I'm hoping it helps sort out overlapping source radiations)
>
>Yet another upgrade of the ultrasonic unit.
>
>Comments are welcome, even if it's to tell me I'm clueless! :)
>
>73
>--
>Paul Kelley, N1BUG
>RFI Committee chair,
>Piscataquis Amateur Radio Club
>http://www.k1pq.org
>_______________________________________________
>Stew Perry Topband Distance Challenge coming on December 29th.
_______________________________________________
Stew Perry Topband Distance Challenge coming on December 29th.
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