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Re: [RFI] portable flag tracking RFI

To: Don Kirk <wd8dsb@gmail.com>, N4ZR <n4zr@comcast.net>
Subject: Re: [RFI] portable flag tracking RFI
From: AA5CT via RFI <rfi@contesting.com>
Reply-to: AA5CT <jwin95@yahoo.com>
Date: Mon, 24 May 2021 02:48:36 +0000 (UTC)
List-post: <mailto:rfi@contesting.com>
JUST remember, if you are within 1/4 wavelength of a source, the 
bearings taken may be off! Until a 'field' has a chance to 'expand'
beyond 1/4 Lambda 'near field' effects involving E and H fields can
dominate affecting what is 'seen' with DF gear ... also, when you 
are under overhead power lines (usually with a lower neutral wire 
on distribution circuits) one will also see these 'direction distortions'.
I have seen this when using the marine radio direction finders ...

This 1/4 wavelength 'thing' can be used to advantage too, if the same 
noise is present higher in frequency - a higher frequency has a smaller 
1/4 wavelength! I use this to advantage when getting close to a source
by moving in frequency from below 2 MHz up to near 6 MHz giving a 
3:1 reduction in wavelength.

Happy hunting!

de AA5CT Jim






On Sunday, May 23, 2021, 6:27:26 PM GMT-5, N4ZR <n4zr@comcast.net> wrote: 





Hi Don - thanks for all your hand-holding.  Finished mine today and it 
works fine.  I used 1" PVC pipe for the arms, and screwed them to either 
side of a 1X6.  I figured the 3/4" offset wouldn't matter, and it 
appears I was right.  With the MTM Scientific W7IUV preamp and a TECSUN 
PL-880 receiver, it easily picked up the 5-8 MHz, every-50-KHz signal 
I've been trying to find, and localized it (by ear) to within about 20 
degrees of arc.  Tomorrow I'm going on the road to triangulate it and 
move in.

I'm really curious to see what it is.  It looks like this:


As you can see, it's not deafening, and I was a little worried that the 
flag+RX sensitivity might not be enough, even with the preamp, but there 
is plenty of signal.


-- 
73, Pete N4ZR
Check out the new Reverse Beacon Network
web server at <http://beta.reversebeacon.net>.
For spots, please use your favorite
"retail" DX cluster.

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