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 <[email protected]> >Subject: Topband: Another take on power line noise hunting >To: Topband <[email protected]> > >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.
