[RFI] MFJ-856 oddity
Hisashi T Fujinaka
htodd at twofifty.com
Tue Aug 7 22:30:45 PDT 2012
Cool. Thanks for all your efforts. I've only had mine out once and I
narrowed down the area (which happened to be right in front of my house)
and I'm on my way to building an ultrasonic receiver out of a kid's
directional microphone. You went up in frequency and I'm going down. :)
On Tue, 7 Aug 2012, N1BUG wrote:
> Thanks Michael,
> I appreciate your comments. This situation with the attenuator
> having no affect in a few areas is something I want to understand
> because I hate things I don't understand! Most of the time, even
> standing directly under the line, there is no such effect. Only in a
> few specific spots does it act that way, and all of those have a
> similar noise signature which is quite different from most other
> sources. That makes me curious.
> Overall, after more than 150 hours in the field with the 856 I've
> decided in my case it is mostly a tool for locating poles with mild
> noise and for getting to the general vicinity of the really bad
> ones. I've been unable to get readings that vary enough to isolate
> the source pole in many cases. I think you may have hit on the
> problem. I can get equidistant from two poles, but I cannot get
> anywhere near that same distance out from under the power line.
> I'm finding the solution is UHF (445 MHz) where I have been able to
> clearly isolate the source pole in all but two cases. Both of those
> involve poles less than 50 feet apart.
> On 08/07/2012 08:07 AM, RFI Services' Michael Martin wrote:
>> I have an 856 and have not experienced this issue.
>> Never stand under the power line with the receiver. The antenna for the
>> noise will be over the antenna for the receiver and the yagi will be like a
>> ball of aluminum instead of a well-designed directional antenna.
>> When looking at signal levels from utility poles remember the antenna for
>> the noise is the poles. Maintain equal distance from the "Two" poles you are
>> comparing. Don't stand under the power line while performing this RF level
>> test or the power line and every other wire will become the antenna for the
>> Maintain equal distances between 2 poles and as close to the same distance
>> away from being under the wires. In the search for power line noise make
>> your measurements a comparison between two poles and reduce your gain until
>> you can easily determine which of the two poles has the highest signal from
>> the arcing source. If the higher signal is from the pole to the left, the
>> move to the left between the next two poles and repeat the process.
>> Most importantly is to tell your power company to call me! I had to throw
>> that in there.
>> One thing I did to my receiver, and I really don't know if it made a
>> difference, was I lined the inside with aluminum foil tape to help shield
>> it. It just made sense to do this due to the fields.
>> I just tried out a new antenna for DFing power line noise and I can't
>> believe how affective it is. It's made by a company called Telonics and it
>> looks like 4 quarter wave rubber duck antennas on a boom. They refer to it
>> as an H design antenna (for some reason). I have never purchased an antenna
>> that performed as well without modification. I'm in the field and don't have
>> the model number with me but it will soon be on my web site. If you call
>> them ask for Phil and tell him I sent you. He'll know the antenna. They are
>> designing one for me that is centered at 143MHz. This allows max gain on a
>> frequency. that won't have traffic.
>> Best wishes,
>> Michael C. Martin
>> RFI Services
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Hisashi T Fujinaka - htodd at twofifty.com
BSEE(6/86) + BSChem(3/95) + BAEnglish(8/95) + MSCS(8/03) + $2.50 = latte
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