Dave ~
Adding a spectrum analyzer should be interesting.
Getting it all configured for easy use in the field is the next logical
step.
I hope it is broadbanded. While the SWR measured 1.1 to 1 from 160 past 10
meters . . . I'm not sure that means it is truly broadbanded.
When viewing a power line source I noticed that its strength was not
uniformly the same across the 9 MHz I was looking at. However, that could
be caused by resonance along the power lines.
I don't know - but it's all getting easier than it used to be.
~ Alan K0AV
On Mon, Apr 12, 2021 at 1:56 PM Dave Cole <dave@nk7z.net> wrote:
> Hi,
>
> You sir are a mind reader, I just started working on a FLAG for just
> this sort of setup-- portable use of a broadband antenna.
>
> I am happy to hear it is as broadband as you say... I will be taking it
> and my SDR on a few walking trips soon...
>
> Being able to see 10 or so MHz. of spectrum is enlightening as hell once
> you start seeing your RFI on more than one band at a time... When you
> dip one source, you see many signals dip at the same time, and you
> realize they are all related! That and they all look the same, just
> shifted in frequency. :)
>
> That blog post you cited, (and thank you for that), is part II of a
> three part blog entry...
>
> Part I covers setup and use of the SDR for this sort of thing, and is at:
>
> https://www.nk7z.net/sdr-rfi-survey-p1/
>
>
> Dave (NK7Z)
> https://www.nk7z.net
> ARRL Volunteer Examiner
> ARRL Technical Specialist, RFI
> ARRL Asst. Director, NW Division, Technical Resources
>
> On 4/12/21 8:56 AM, Alan Higbie wrote:
> > In the past few days I've started using a Flag Loop antenna (designed by
> > WD8DSB).
> >
> > I supplement it by also using a National RF HF-DF bidirectional loop.
> >
> > The patterns on both have been confirmed by using a known signal source
> (RF
> > signal generator).
> >
> > Having a unidirectional antenna is very helpful. The null of the
> > cartioid pattern is quite pronounced.
> >
> > Example: for years now, I have had a noise source which seemed to be
> coming
> > from 40 deg. at times - and other times coming from 220 deg. I believe
> > that the results had been confounded by re-radiation along the power
> lines. Now
> > I have now definitely determined that it is from 220 deg. (i.e. a giant
> > step closer to location and resolution).
> >
> > An ** interesting feature ** of the Flag Loop is that it is broadbanded -
> > maintaining its directional properties over a big chunk of spectrum.
> > Unlike a tuned loop (or tuned yagi), a broadband antenna allows you to
> view
> > a huge piece of spectrum at once. And with an SDR this is quite easy -
> and
> > very interesting.
> >
> > Dave, NK7Z, has a blog where he describes using an SDR to make site RFI
> > survey. He was using a fixed broadband antenna.
> >
> > Look at Dave's work on this subject:
> > https://www.nk7z.net/rfi-site-survey-part-ii-interpretation/
> >
> > Having a broadband and unidirectional ROTATABLE antenna allows us to
> > quickly and more definitively see associations among the various sources.
> > And, simultaneously begin to find the RFI source.
> >
> > Yesterday I set my SDR to receive a section of spectrum from 3.0 to 11.0
> > MHz. Then I rotated the Flag Loop - - and the results were very
> > interesting: I could see some very strong and wide signals. These
> > appeared across the spectrum and which rose-and-fell together (meaning
> they
> > are from the same device). I had not realized that junk was there.
> >
> > Still don't know if these wide signals are ACTUALLY AFFECTING MY
> RECEIVER'S
> > NOISE FLOOR on any band. To be determined. Interesting nonetheless.
> >
> > *Why this matters*: a broadband / unidirectional antenna with SDR now
> > allows a view of what kind of RFI is really out there.
> >
> > 73, Alan K0AV
> > _______________________________________________
> > RFI mailing list
> > RFI@contesting.com
> > http://lists.contesting.com/mailman/listinfo/rfi
> >
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