[RFI] Guidance on finding noise?

[Michael Martin]

Hey Scott,
The next time you DF a power line noise pay close attention to your distance away from the pole. By moving back and forth, a half a wavelength of the freq you're using, you'll notice you can go in and out of the peaks. Once you're at the peak signal level, I think you'll notice that when you're at the source your antenna is actually diagonally polarized. if you're horizontally polarized you're usually much further away from the source. As you approach the power line source you'll find your signal level, using a yagi, is strongest in the diagonal position.
If you don't mind let me know your findings.

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On Jan 13, 2020, 12:12 AM, at 12:12 AM, K9MA <k9ma at sdellington.us> wrote:
>With any kind of direction finding antenna, you have to be aware of 
>polarization. A vertically polarized loop, for example, may give very 
>misleading bearings if the noise happens to be mostly horizontally 
>polarized. When I walk around with my 135 MHz yagi tracker, I rotate
>its 
>polarization as I sweep around in azimuth, and often find the most 
>distinctive peak with it mostly vertically polarized.
>
>73,
>Scott K9MA
>
>
>
>
>On 1/12/2020 15:18, AA5CT via RFI wrote:
>>   This may be a case where the marine DF receiver succeeds, and a
>> simple DF loop fails.
>>
>>
>> With the simple DF loop one is unable, repeat, *unable* to resolve
>> the __180 degree ambiguity__ that the 'null' of a simple loop gives.
>>
>>
>> The BIG, and this is NO slight advantage offered by the marine DF
>> receiver is the utilization of a "sense" antenna that works in
>combination
>> with the built-in loop antenna to 'synthesize' a cardioid or
>unidirectional
>> antenna pattern.
>>
>>
>> WITH THIS feature one can actually 'sweep' around the compass rose
>> and get a feel for where the strongest noise is coming from, like
>pointing
>> a Yagi antenna around, but on 160 or 80 meters! On the other hand,
>the
>> simple loop can ONLY give a one a NULL, and there remains the choice
>> of which direction, which bearing the 'source' lines in, because of
>that
>> 180 degree ambiguity.
>>   
>>
>> Also with the simple loop one cannot 'scan around' for the strongest
>> signal, whether that signal is a 'broad band' white noise (LIKE I get
>> from a car wash in my area) OR impulse 'buzz' noise from power
>> line arcing sources.
>>
>>
>> IT REALLY IS pretty cool to 'twirl' the direction knob on one of
>these
>> Coastal Navigator Marine DF receivers and HEAR the different 'arc'
>> signatures or sounds coming from different directions.
>>
>>
>> Maybe this is where we're getting hung up up? All my DFing for
>> any noise nowadays makes use of the marine DF receiver with the
>> sense antenna and that directional Cardioid pattern.
>>
>>
>> If IT emits, its a simple matter of taking two bearings sufficiently
>> spatially spaced apart and "x" marks the spot of the source. I now
>> use Google maps and 'null' bearings taken from my DF receivers
>> to pinpoint distant sources.
>>
>>
>> One technique I've used too is to 'set out' after one of these
>sources on
>> my trail bicycle, and through the use of null DFing and the
>Sense/Cardioid
>> function eventually locate OR determine the source is further way
>than
>> first thought. If I get down the road a mile or so AND the DF
>receiver is
>> still indicating the SAME direction, I'm looking at a source that is
>now
>> on the order of 4 to maybe 5 miles way, and as I've written, I've had
>a
>> couple just like that!
>>
>>
>> de AA5CT
>>
>> .
>> .
>>       On Saturday, January 11, 2020, 9:03:04 PM CST, Kenny Silverman
><kenny.k2kw at gmail.com> wrote:
>>   
>>   KC4D,N3AC and N3CW went hunting with a KX3 and a DX Engineering
>Amplified RX loop and again didn’t find anything conclusive. Basically
>they said the loop performed about the same as one of the AM radios we
>have that’s fairly directional.
>>
>> We’ve been looking so many times that we’re getting frustrated. 
>There are a few noisy clusters, but we can’t find a specific pole or
>house.  Nor can we assess if the noisy areas are actually the key
>offender(s)
>>
>> Do we call in the clusters we found ?  Or do we really need to
>pinpoint the source(s) better before we ask for crews to come out? 
>We’re concerned about crying wolf and/or giving a list of more than a
>dozen poles for the power company to look at.
>>
>> Regards , Kenny K2KW
>>
>> P.S.  the only success so far is fixing my subject line typo 🤓
>> _______________________________________________
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>
>
>-- 
>Scott  K9MA
>
>k9ma at sdellington.us
>
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