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Re: [loopantennas] Advice on Direction Finding Loop for UHF

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  • Stanley Reynolds
    Either a Moxon Rectangle antenna, or a Yagi would work better as you would have a null or peek in one direction. http://www.ac6la.com/moxgen.html Stanley
    Message 1 of 10 , Aug 19, 2009
      Either a Moxon Rectangle antenna, or a Yagi would work better as you would have a null or peek in one direction.

      http://www.ac6la.com/moxgen.html

      Stanley
    • Andy
      This is not meant to be an endorsement (and I have no experience with this model) ... but Arrow Antennas sells a small loop that includes UHF:
      Message 2 of 10 , Aug 20, 2009
        This is not meant to be an endorsement (and I have no experience with
        this model) ... but Arrow Antennas sells a small loop that includes
        UHF:

        http://www.arrowantennas.com/fhl.html
        http://www.arrowantennas.com/loopdemo.html

        They appear to be "shielded" loops (though the mention of a "Faraday
        shield" is incorrect, it is not a true Faraday shield, if it were the
        antenna would not receive at all), and they probably contain a balun
        in the base to maintain the loop's balance (essential for good DF
        nulls). Given the frequency ranges (no lower limit), and the diagram
        showing the null perpendicular to the plane of the loop, these would
        be small loops.

        Andy
      • Frits PE2G
        Thanks, Stanley and Andy, for your suggestions. The small loop from Arrow Antennas looks most promising to me. I usually know in which general direction I have
        Message 3 of 10 , Aug 23, 2009
          Thanks, Stanley and Andy, for your suggestions. The small loop from Arrow
          Antennas looks most promising to me. I usually know in which general
          direction I have to search, the problem is the final stage of the search,
          when the radiosonde is somewhere on the terrain at a range of <100 meters.
          When the transmitter is at close range, but still invisible in the
          vegetation, I need a sharp null.

          73,
          Frits PE2G
        • Richard (Rick) Karlquist
          Arrow Antennas makes an ultra light weight 2 meter/440 MHz portable Yagi with a handle for satellite work. It is also great for direction finding. It breaks
          Message 4 of 10 , Dec 18, 2009
            Arrow Antennas makes an ultra light weight 2 meter/440 MHz
            portable Yagi with a handle for satellite work. It is
            also great for direction finding. It breaks down and fits
            in a carrying case. Highly recommended.

            Rick N6RK

            Stanley Reynolds wrote:
            >
            >
            > Either a Moxon Rectangle antenna, or a Yagi would work better as you
            > would have a null or peek in one direction.
            >
            > http://www.ac6la.com/moxgen.html <http://www.ac6la.com/moxgen.html>
            >
            > Stanley
            >
            >
          • Tracey Gardner
            I can t see it on their web site Rick Regards Tracey
            Message 5 of 10 , Dec 18, 2009
              I can't see it on their web site Rick

              Regards

              Tracey



              > Arrow Antennas makes an ultra light weight 2 meter/440 MHz
              > portable Yagi with a handle for satellite work. It is
              > also great for direction finding. It breaks down and fits
              > in a carrying case. Highly recommended.
              >
              > Rick N6RK
              >
              > Stanley Reynolds wrote:
              >>
              >>
            • Tracey Gardner
              Sorry Rick, I ve now put my glasses on and found it :-) Regards Tracey
              Message 6 of 10 , Dec 18, 2009
                Sorry Rick, I've now put my glasses on and found it :-)

                Regards

                Tracey



                > Arrow Antennas makes an ultra light weight 2 meter/440 MHz
                > portable Yagi with a handle for satellite work. It is
                > also great for direction finding. It breaks down and fits
                > in a carrying case. Highly recommended.
                >
                > Rick N6RK
                >
                >
              • aajham
                A great 440 antenna is 4 ele quad antenna on 440 using copper clad steel and a single spreader. Make them round and its pretty easy and small. Good luck,
                Message 7 of 10 , Dec 19, 2009
                  A great 440 antenna is 4 ele quad antenna on 440 using copper clad steel and a single spreader. Make them round and its pretty easy and small.

                  Good luck, Art.

                  --- In loopantennas@yahoogroups.com, "Tracey Gardner" <tracey.gardner@...> wrote:
                  >
                  > Sorry Rick, I've now put my glasses on and found it :-)
                  >
                  > Regards
                  >
                  > Tracey
                  >
                  >
                  >
                  > > Arrow Antennas makes an ultra light weight 2 meter/440 MHz
                  > > portable Yagi with a handle for satellite work. It is
                  > > also great for direction finding. It breaks down and fits
                  > > in a carrying case. Highly recommended.
                  > >
                  > > Rick N6RK
                  > >
                  > >
                  >
                • bm40g
                  ... Hello Frits, The final phase of a search can be done with attenuators. Once your close, throw in 20 dB of attenuation, then 40, and so on. A 100 dB
                  Message 8 of 10 , Dec 20, 2009
                    --- In loopantennas@yahoogroups.com, "Frits PE2G" <pe2g@...> wrote:
                    >
                    > Thanks, Stanley and Andy, for your suggestions. The small loop from Arrow
                    > Antennas looks most promising to me. I usually know in which general
                    > direction I have to search, the problem is the final stage of the search,
                    > when the radiosonde is somewhere on the terrain at a range of <100 meters.
                    > When the transmitter is at close range, but still invisible in the
                    > vegetation, I need a sharp null.
                    >
                    > 73,
                    > Frits PE2G
                    >

                    Hello Frits,

                    The final phase of a search can be done with attenuators. Once your close, throw in 20 dB of attenuation, then 40, and so on. A 100 dB switched atenuator, and very good shielding between the attenuator and the radio, and of the radio itself (aluminum foil?) are required for transmitters that are more than about 1 watt.

                    One technique is to do the spiral search. Which was taught to me by a pilot. Proceed on a bearing from far out as best as you can tell directly towards the target. Stay on the same bearing without turning, until your antenna indicates a 90 degree variation from the original bearing. Then turn in that direction 90 degrees. Proceed on the new bearing again, until the antenna indicates 90 degree deviation from the bearing. Duplicate this over and over, with more and more attenuation, and even with a yagi you cannot help but walk right into the target.
                  • ab2nj
                    The spiral search pattern is a good technique to keep in mind. It can be an effective tool in your bag-O-trick for RDFing. While the importance of shielding
                    Message 9 of 10 , Dec 21, 2009
                      The "spiral" search pattern is a good technique to keep in mind. It can be an effective tool in your bag-O-trick for RDFing.

                      While the importance of shielding everything behind the attenuator cannot be over emphasized for "close-in" work, a much better approach (and a another handy tool) is the use of an "Offset Attenuator." Arrow makes one that works well and there are simple kits for low cost. Do a Google Search for "Offset Attenuator" and you'll see how they work.

                      Briggs Lonbothum, ab2nj
                      Gloucester, Ma. FN42pp
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