[RFI] Flag Pennant loop - added benefit of being broadband

[Dave Cole]

I have a more reliable SA on my bench, I will be doing some compairs to 
the tinySA, although there is a fellow on YouTube that used a decent HP, 
and the tinySA is fairly decent if you watch input levels...  I have a 
preamp I am building for the mess...  I want a small single box I can 
put on the antenna...  :)

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources

On 4/12/21 1:44 PM, Alan Higbie wrote:
> 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 at nk7z.net 
> <mailto:dave at 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 at contesting.com <mailto:RFI at contesting.com>
>      > http://lists.contesting.com/mailman/listinfo/rfi
>      >
>     _______________________________________________
>     RFI mailing list
>     RFI at contesting.com <mailto:RFI at contesting.com>
>     http://lists.contesting.com/mailman/listinfo/rfi
>