[RFI] Ultra Sonics

Mon Apr 22 21:48:27 EDT 2013

Just about every full feature handheld offered to the Amateur market today has a receiver that covers .5 to 470 MHz or 1 GHz. A 3 element yagi for 150 MHz is easy to build (or buy). An attenuator is very helpful. Coax connects the yagi to the attenuator and the attenuator to the radio. This basic setup should be able to pinpoint a source to a pole or a house. 

In my opinion, the MFJ RFI searching device is only marginally useful unless you actually have some idea how to DF radio signals. RFI is a radio signal. You DF RFI much the same way you DF any signal. 

You need a receiver that can listen on the affected frequency in AM mode and has some means of showing signal strength. A directional antenna at the frequency of interest is very useful. A means of keeping the maximum signal strength indication at about midscale is required. That means the receiver must have an attenuator or an external attenuator must be used. 

Practice on known signals to develop skill. Then set out to locate the RFI. 

Used radios can be had for under $200. Suitable yagi antennas cost less than $30 in materials to build. Attenuators can be bought or made. Storebought attenuators can be expensive. Homemade attenuators can be cheap and effective. At hamfests I find all kinds of professional attenuators for $10 and up. Coax jumpers with BNC connectors are not usually expensive. 

Hope this helps. Good luck.

73,  Frank KB4T

Sent from somewhere in Frank's electronic universe

On Apr 21, 2013, at 10:54 PM, Gary Mayfield <gary_mayfield at hotmail.com> wrote:

> Frank,
>  
>  
> This is good to know.
>  
>  
> Is there anything you would recommend starting with?  My father is deperate to find the noise in his little town.  The utility has been out three times, and of course each time was immediately after a rain and the noise was not present.  Most days it S9 or better accross the bands.  The last time I was down there it seemed like it was coming from all directions.
>  
>  
> He has the MFJ handheld unit, but he hasn't had much luck with it.
>  
>  
>  
> Thanks and 73,
>  
> Joe
>  
>  
>  
> > Date: Sun, 21 Apr 2013 21:18:46 -0400
> > From: utility.rfi.pro at gmail.com
> > To: paul at n1bug.com
> > CC: rfi at contesting.com
> > Subject: Re: [RFI] Ultra Sonics
> > 
> > I have all of the Radar Engineers equipment. As a utility interference
> > investigator I'm fortunate to have good tools. The ultrasonic unit is only
> > useful AFTER I've already found the source pole. Even then the ultrasonic
> > detector is able to hear the actual source only 40% of the time.
> > 
> > The ultrasonic detector is not able to hear arcing inside a transformer or
> > any other device where the arcing is inside a metal or plastic
> > case/container.
> > 
> > Frankly I could do my job just fine without the ultrasonic detector. With
> > its low productivity and limited usefulness, my success rate would be
> > impacted only slightly.
> > 
> > Spend money on tools that will do the most for you. By that I mean
> > directional indicating equipment that will pinpoint the pole, house or
> > structure. If the source is a pole, a crew will touch everything until the
> > source is found and corrected. If the source is in a house or other
> > structure you will use a small receiver possibly equipped with a
> > directional antenna to walk up to the source.
> > 
> > Save the ultrasonic purchase for last.
> > 
> > 73,
> > 
> > Frank N Haas KB4T
> > Utility RFI Investigator
> > Florida
> > Disclaimer: I was on the beta test team for the RX3.
> > 
> > The RX3 is a huge improvement over the RX2. I have not tested the RX1 but
> > looking at the schematic I suspect the RX3 would beat it by a wide margin.
> > In tests with a controlled spark source, the stock RX2 (predecessor to the
> > RX3) with 12 inch dish could detect the spark to a distance of 35 feet. The
> > RX3 with the same dish could detect it at 100+ feet.
> > 
> > I would definitely go with the larger dish. Actually I would prefer 18 inch
> > were it available. I will add that I am very disappointed in the quality of
> > the dish, which I have communicated to the proprietor on several occasions.
> > The detector used requires a very flat dish. Upgrading/modifying using one
> > of the other dishes available on the market has not proven practical
> > because they are all too deep and/or just just as poor in conforming to
> > parabolic shape as the supplied dish. At some point when my budget allows,
> > I plan to try a deeper/better/larger dish with a different detector (one
> > having a wider acceptance angle or "beamwidth").
> > 
> > Outside the scope of your question: I would NOT use ultrasonics to FIND
> > noisy poles. You want radio receivers for that. Use the ultrasonic to
> > verify and find specific hardware that is sparking once you have located
> > the pole.
> > 
> > 73
> > 
> > -- 
> > Paul Kelley, N1BUG
> > RFI Committee chair,
> > Piscataquis Amateur Radio Club
> > http://www.k1pq.org
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