[RFI] MFJ-856 oddity

EDWARDS, EDDIE J eedwards at oppd.com
Wed Aug 8 07:27:20 PDT 2012


I think one of our techs at work who is also a ham assembled an ultrasound kit with a dish.  He found it really didn't work well enough to be much help doing RI tracking on electric power poles.  He found that using higher RF freqs worked better in his case.  

At work we just purchased a new ultrasonic receiver from Radar Engineers to replace our old broke down UE Systems unit.  Once our RFI tech gets some experience with it, I'll try to give an update on it sometime.

73, de ed -K0iL

-----Original Message-----
From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com] On Behalf Of Hisashi T Fujinaka
Sent: Wednesday, August 08, 2012 12:31 AM
Cc: rfi at contesting.com
Subject: Re: [RFI] MFJ-856 oddity

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.
> Paul
> 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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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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