[RFI] MFJ-856 oddity

N1BUG paul at n1bug.com
Tue Aug 7 13:24:31 PDT 2012

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
> noises.
> 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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