[RFI] Flag Antenna Question
Dave (NK7Z)
dave at nk7z.net
Wed Feb 1 20:23:35 EST 2023
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 at nk7z.net
> <mailto: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 <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>
> > <mailto: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> <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 at gmail.com <mailto:wa2sqq at gmail.com>
> <mailto: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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