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Re: [RFI] Flag Antenna Question

To: Don Kirk <wd8dsb@gmail.com>
Subject: Re: [RFI] Flag Antenna Question
From: "Dave (NK7Z)" <dave@nk7z.net>
Date: Wed, 1 Feb 2023 17:23:35 -0800
List-post: <mailto:rfi@contesting.com>
Thanks Don!! I will read up on that... I am thinking the flag will work better as it does not have lobes in two directions, like the loop... That way, I can null my RFI source better. I have only one right now... That will of course change... In any case, thank for the direction, something new to read!! :)

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 16:20, Don Kirk wrote:
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@nk7z.net <mailto:dave@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 <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@nk7z.net
    <mailto:dave@nk7z.net>
     > <mailto:dave@nk7z.net <mailto:dave@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> <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/>
     >     <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@gmail.com <mailto:wa2sqq@gmail.com>
    <mailto:wa2sqq@gmail.com <mailto:wa2sqq@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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