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

[Dave Cole]

BTW:

I am currently working on setting up a tinySA on the FLAG...  Try it, it 
is really portable.  The tinySA will mount right on the support pole for 
the FLAG.  No computer, no SDR, just a box the size of a pack of smokes...

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 12:56 PM, Dave Cole 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
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