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Advice on Direction Finding Loop for UHF

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  • Frits PE2G
    Hello all, I m new on the list. I m contemplating to build a (small) loop antenna for Direction Finding on UHF, mainly because of its simplicity and handy
    Message 1 of 10 , Aug 19, 2009
      Hello all,

      I'm new on the list.

      I'm contemplating to build a (small) loop antenna for Direction Finding on
      UHF, mainly because of its simplicity and handy size. The freqs used are
      in the 401-406 MHz band (weather sondes in Europe) with a center freq of
      403 MHz. The loop should provide a good null on a signal from a radiosonde
      that is already on the ground and at close range.

      Would you recommend a full wave loop or one smaller than that?

      Any other suggestions are appreciated!

      Many thanks and 73,

      Frits PE2G
      JO32HI
    • 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 2 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 3 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 4 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 5 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 6 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 7 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 8 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 9 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 10 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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