[RFI] Flag Antenna Question

[Don Kirk]

Hi Dave,

You won’t yield half the noise, and it’s a complicated topic but I suggest
you read up on what’s called RDF (receiving directivity Factor) and this
was a concept that I believe W8JI first introduced.  RDF gives an
approximation on the signal to noise merits of receive antennas but that’s
based on noise arriving equally from all directions which is often not the
case.  I’m not sure what the RFF value is for a bidirectional loop but the
RDF for pennants and flags is approximately 7.8.  Often you will be dealing
with local noise arriving from one direction and if that’s the case then a
pennant or flag is best for rejection of noise arriving 180 degrees from
the direction of your desired signal whereas your loop has a deep null off
the side so its best for rejecting noise arriving 90 degrees to the
direction of the signal of interest.

Don wd8dsb

On Wed, Feb 1, 2023 at 6:04 PM Dave (NK7Z) <dave at nk7z.net> wrote:

> Cool...  I am thinking of comparing it to a Mag loop.  I am setting up a
> RX only antenna for my K4, and suspect the cardioid pattern will do far
> better than the pattern from a mag loop.  Half the noise...  :)
>
> 73, and thanks,
> Dave (NK7Z)
> https://www.nk7z.net
> ARRL Volunteer Examiner
> ARRL Technical Specialist, RFI
> ARRL Asst. Director, NW Division, Technical Resources
>
> On 2/1/23 13:39, Don Kirk wrote:
> > Hi Dave,
> >
> > I have not but I believe it should work (especially since a diamond
> > works).  You can look at other configurations that are known to work by
> > reading the original article about Pennant and Flag receive antennas by
> > Earl K6SE (SK) in the July 2000 issue of QST.  I designed my portable DF
> > antenna as a rectangle because I wanted the most gain possible that
> > would still fit easily in my car.
> >
> > 73,
> > Don (wd8dsb)
> >
> > On Wed, Feb 1, 2023 at 3:50 PM Dave (NK7Z) <dave at nk7z.net
> > <mailto:dave at nk7z.net>> wrote:
> >
> >     Don,
> >     Have you tried your design with a loop as opposed to the rectangle?
> >
> >     73, and thanks,
> >     Dave (NK7Z)
> >     https://www.nk7z.net <https://www.nk7z.net>
> >     ARRL Volunteer Examiner
> >     ARRL Technical Specialist, RFI
> >     ARRL Asst. Director, NW Division, Technical Resources
> >
> >     On 2/1/23 12:09, Don Kirk wrote:
> >      > Hi Bob,
> >      >
> >      > Dave (W0LEV) provided you good insight.  Normally I say just stay
> >     away from
> >      > wire wound resistors as we know they are definitely inductive,
> >     and carbon
> >      > resistors are just fine.
> >      >
> >      > Any value of termination resistor between 680 ohms and 820 ohms
> will
> >      > provide good results for use on my portable flag.  There are just
> >     slight
> >      > trade offs between how a 680 and 820 resistor perform and you can
> >     see front
> >      > to back ratio versus elevation plots showing how the 680 ohm
> >     resistor and
> >      > 820 ohm resistor model.  I actually have two identical portable
> >     flags, one
> >      > with a 680 ohm termination resistor and one with a 820 ohm
> >     termination
> >      > resistor and you would be hard pressed telling the difference
> >     unless I told
> >      > you what to look for in performance.  You can see the plots on my
> >     portable
> >      > flag website at
> >     https://sites.google.com/site/portableflagantenna/
> >     <https://sites.google.com/site/portableflagantenna/>
> >      >
> >      > 73,
> >      > Don wd8dsb
> >      >
> >      > On Wed, Feb 1, 2023 at 2:26 PM Bob Kozlarek WA2SQQ
> >     <wa2sqq at gmail.com <mailto:wa2sqq at gmail.com>> wrote:
> >      >
> >      >> I started putting together one of your portable flag antennas.
> >     Regarding
> >      >> the resistor that is used by notice it’s called out as a
> >     non-inductive
> >      >> resistor. Is this something special or with a standard carbon
> >     comp or
> >      >> carbon film resistor work? If this is something that is super
> >     critical I’m
> >      >> thinking that I could put two or more larger values in parallel
> >     to arrive
> >      >> to desire value.--
> >      >>
> >      >>
> >      >>
> >      >> *Best 73 de WA2SQQElmwood Park, NJ"The only dumb questions are
> >     those we
> >      >> don't ask"*
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