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Re: [loopantennas] Loop questions?

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  • Andy
    The nulls that you get perpendicular to the plane of the loop, are characteristic of small loops only, much less than a wavelength circumference. Full size
    Message 1 of 16 , Dec 21, 2006
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      The nulls that you get perpendicular to the plane of the loop, are
      characteristic of small loops only, much less than a wavelength
      circumference.

      Full size loops, on the order of one wavelength circumference, behave
      exactly the opposite to this, with the most reception where small loops have
      a null.

      So the less a loop is electrically small (or the higher you go in frequency
      for a fixed size), the poorer the null tends to become.

      Andy
    • John Stumm
      ... greater ... Steve A spiral wound loop will inherently produce better nulls. I m surpised that nobody has mentioned this.
      Message 2 of 16 , Dec 21, 2006
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        --- In loopantennas@yahoogroups.com, "Steve B." <mcqueen_34@...> wrote:
        >
        > I would like to build a loop to optimize the nulling effects but I'm
        > not sure what produces a greater null. Will a loop with a larger
        > diameter create greater nulls; will a loop with higher Q create
        greater
        > nulls? Does any one have any experience with this?
        >
        Steve
        A spiral wound loop will inherently produce better nulls. I'm surpised
        that nobody has mentioned this.
        http://f1.grp.yahoofs.com/v1/oMuKRa5H8wSSm2qH8L7eeNVGXtyE374L2XNxhIOp69g
        PSNy2SQgw-PRMI_oUA_OKWmNktnn_7cJU-
        cdolPoCaVCNLKCexiOBuYQ/JohnsLoopDaJour/Spiraloop.JPG

        john
      • Andy
        ...
        Message 3 of 16 , Dec 23, 2006
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        • Marc
          ... Sorry, even when I copy paste the complete link, it does not work ... Isn t there a shorter version?? In wich discussion group can I find the picture ??
          Message 4 of 16 , Dec 27, 2006
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            John Stumm wrote:
            > --- In loopantennas@yahoogroups.com, "Steve B." <mcqueen_34@...> wrote:
            >
            >> I would like to build a loop to optimize the nulling effects but I'm
            >> not sure what produces a greater null. Will a loop with a larger
            >> diameter create greater nulls; will a loop with higher Q create
            >>
            > greater
            >
            >> nulls? Does any one have any experience with this?
            >>
            >>
            > Steve
            > A spiral wound loop will inherently produce better nulls. I'm surpised
            > that nobody has mentioned this.
            > http://f1.grp.yahoofs.com/v1/oMuKRa5H8wSSm2qH8L7eeNVGXtyE374L2XNxhIOp69g
            > PSNy2SQgw-PRMI_oUA_OKWmNktnn_7cJU-
            > cdolPoCaVCNLKCexiOBuYQ/JohnsLoopDaJour/Spiraloop.JPG
            >


            Sorry, even when I copy paste the complete link, it does not work ...
            Isn't there a shorter version?? In wich discussion group can I find
            the picture ??

            Marc

            --
            --
            Apres l'emission "faux" par la RTBF, le Premier Ministre Flamand Yves Leterme s'est exprime contre le journal "Liberation":
            "Le peuple Belge n'a pas les capacites intellectuelles pour discuter sur le sujet de la scission".
          • Andy
            ... Andy
            Message 5 of 16 , Dec 27, 2006
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              > Sorry, even when I copy paste the complete link, it does not work ...
              > Isn't there a shorter version?? In wich discussion group can I find
              > the picture ??

              See my reply that came a few days ago:

              > http://groups.yahoo.com/group/loopantennas/files/JohnsLoopDaJour/
              >
              > and scroll down to Spiraloop.JPG

              Andy
            • Steve
              That is because Yahoogroups doesn t allow linking directly to any files or photos, they do it by using dynamic links. Click on a file or photo, wait 30 minutes
              Message 6 of 16 , Dec 27, 2006
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                That is because Yahoogroups doesn't allow linking directly to any
                files or photos, they do it by using dynamic links. Click on a file or
                photo, wait 30 minutes and hit "Reload" on your browser and it'll say
                it doesn't exist. Hit "Back" on your browser so you are back in the
                folder, hit "Reload", then click on the file or photo again and it
                works again.

                You can get tricky about it, but the simplest way is to only link to
                the folder and then give that link.

                Tricky:
                http://groups.yahoo.com/group/loopantennas/files/JohnsLoopDaJour/Spiraloop.JPG

                Copy the complete URL to the folder, then manually type in the file
                name. That link will work, but after you click on it the Location
                listed in your browser will look like the long incomprehensible
                temporary link below.

                Steve Greenfield
                listowner loopantennas

                --- In loopantennas@yahoogroups.com, Andy <Andy.groups@...> wrote:
                >
                > >
                >
                http://f1.grp.yahoofs.com/v1/oMuKRa5H8wSSm2qH8L7eeNVGXtyE374L2XNxhIOp69gPSNy2SQgw-PRMI_oUA_OKWmNktnn_7cJU-cdolPoCaVCNLKCexiOBuYQ/JohnsLoopDaJour/Spiraloop.JPG
                >
                > This link (patched to fix the line-wrapping) didn't work for me.
                >
                > Go to:
                >
                > http://groups.yahoo.com/group/loopantennas/files/JohnsLoopDaJour/
                >
                > and scroll down to Spiraloop.JPG
                >
                > Andy
                >
              • Richards
                WOW -- Not THAT is quite a loop antenna. I am making one, but it is not that big. Cool. /// Richards ////
                Message 7 of 16 , Dec 28, 2006
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                  WOW -- Not THAT is quite a loop antenna. I am making one, but it
                  is not that big.

                  Cool. /// Richards ////
                  =========================================================

                  Steve wrote:

                  > http://groups.yahoo.com/group/loopantennas/files/JohnsLoopDaJour/Spiraloop.JPG
                • aimo ruoho
                  the ADCOCK ARRAY???????????? ... Have you considered using the Adcock array? It has the best nulls that i have encountered in models and in practice. Another
                  Message 8 of 16 , Dec 31, 2006
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                    the ADCOCK ARRAY????????????

                    CR <vk3he@...> wrote: --- In loopantennas@yahoogroups.com, "Steve B." <mcqueen_34@...> wrote:
                    >
                    > I would like to build a loop to optimize the nulling effects but I'm
                    > not sure what produces a greater null. Will a loop with a larger
                    > diameter create greater nulls; will a loop with higher Q create greater
                    > nulls? Does any one have any experience with this?

                    Have you considered using the Adcock array? It has the best nulls that
                    i have encountered in models and in practice.

                    Another antenna that models very well with a very deep null off the
                    back is the FLAG antenna. The 1 meter high by 2 meter wide flag has a
                    superb pattern from 1 to 30mhz. The gain is very low at the lower
                    frequencies however you can scale it for the frequency range you seek
                    for better gain. After looking at all the patterns i thought i had
                    constructed the model incorrectly, however after contacting K6SE
                    about it he did confirmed that the pattern indeed was excellent. The
                    flag makes a great compact rotable DF antenna using the null.

                    I have been experimenting with super resolution direction finding
                    antennas both loops and active. However the learning curve is very
                    steep since the mathematics and theory is very complex. Also the lack
                    of availability of phase locked receivers makes the job just about
                    impossible.

                    I personally think that rather than creating an electrically perfect
                    antenna that will only hold its pattern over a narrow frequency range
                    you would be far better off investing your eggs in some kind of
                    beamforming array using DSP methods. Even a accurate phasing system
                    would work.

                    This link below is a great introduction to a simple beam stearing
                    system for noise reduction. As the author demonstrates phase
                    selectivity with DSP is very effective. Using the same techniques DSP
                    direction finders can pin point a signal with 1 degree accuracy using
                    small aperture loops. They can also filter out noise and multiple
                    signals on the same frequencies by phase filterng and processing.

                    I have been trying to build a copy of the Watkins Johnson WJ8976 HF DF
                    system using similar techniques. However progress has been slow
                    because of the sheer lack of information and suitable phase coherent
                    receivers.

                    http://www.pa0sim.nl/index.htm

                    The discussion on the Alford Loop might be of interest to you as well.
                    The nulls look superb from 2 to 30 mhz. I use 4 Alford loops at the
                    moment with a MFJ 1026 phase controller and the results are very
                    impressive. Adding DSP phase comparisons and evaluations to all 4
                    antennas will be the next step. Unfortunately all this science is
                    locked behind a great wall of secrecy, commercial confidentiality and
                    deep research by the leading maths experts of the world. I could
                    just well imagine how well systems like the Rohde and Schwartz works
                    based on my limited experiments with phase selectivity and post
                    processing on HF.

                    Craig





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