Topband: The WD8DSB mini-flag antenna

[Richard (Rick) Karlquist]

For finding 160 meter noise sources, I use a C-Crane or Sangean
pocket AM band radio tuned to 1710 kHz.  It also has a very sharp
null due to the ferrite loop stick antenna built in.  The QST
antenna does have the advantage of being unidirectional, but I
can often triangulate with the pocket radio by walking around
and getting two different null directions.

Rick N6RK

On 2/23/2021 10:25 AM, John Kaufmann via Topband wrote:
> Some of you may have seen the article by WD8DSB in the latest issue of QST.
> I believe WD8DSB is on this reflector.  His article describes a mini-flag
> antenna that can be used for direction-finding.  The neat thing about this
> antenna, besides its compact size, is that it is unidirectional and is very
> broadband.  It works from the AM BCB through 10m.  It produces a sharp null
> off the back which allows you to determine signal direction without the
> direction ambiguity you get with a conventional unterminated loop.
> 
>   
> 
> DX Engineering is producing this antenna as a kit, along with a companion
> preamp.  (Disclaimer:  I have no affiliation or commercial interest in DX
> Engineering).  See:  https://www.dxengineering.com/parts/dxe-noiseloop.  I
> just bought the flag kit last week and finished assembling it this past
> weekend.  I see today that the kit is now back-ordered until April so it was
> good that I ordered it as soon as I saw the QST article.
> 
>   
> 
> It took me about 3 hours to assemble the mini-flag even though the DXE Web
> site says it can be done in 1-2 hours.  There is a bit of fussy mechanical
> assembly involved in getting the symmetry and dimensions just right,
> although it's not hard work.  The flag is 42 inches wide and 21 inches tall.
> The DXE version of the antenna has slightly smaller dimensions than those
> given in the QST article, which results in a small reduction in gain, which
> doesn't really matter, but the pattern is the same.
> 
>   
> 
> I did some testing of the mini-flag in the AM BCB.  The gain is very
> low--about -65 dBi on 160m--so it needs a good preamp.  I used a homebrew
> preamp made up of a couple of MMIC's that produce about 35 dB of gain.  The
> DXE preamp for this antenna won't be available until April.  On the higher
> frequencies, less preamp gain is needed because the gain of the mini-flag
> increases with frequency.
> 
>   
> 
> My initial tests indicate this antenna clearly works.  By rotating the flag
> for the deepest null, I could nail the heading an AM BCB station to a few
> degrees.
> 
>   
> 
> This antenna could also be used as directional receiving antenna on its own.
> Although it is not hugely directive, it can be rotated easily to peak or
> null signals or noise, and it is better than a conventional unterminated
> loop.  It has essentially the same RDF as other larger flag or pennant
> antennas but is obviously far more compact.
> 
>   
> 
> This is a nice contribution by WD8DSB.  Now I have to go off with the
> mini-flag and chase some local noise sources that have been plaguing me this
> winter on the low bands.
> 
>   
> 
> 73, John W1FV
> 
>   
> 
> _________________
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