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Re: loop design and testing

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  • Greg W:-)
    You might want to check out my small loop at http://www.geocities.com/onegammyleg/ as I too live in a noise level area that never drops below S 9+ on SW
    Message 1 of 11 , Jan 4, 2006
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      You might want to check out my small loop at
      http://www.geocities.com/onegammyleg/ as I too live in a noise level
      area that never drops below S 9+ on SW frequencies.
      It is the only thing I have found that even comes close to working in
      this QTH.

      regards

      gregW:-)

      ========================================================================

      --- In loopantennas@yahoogroups.com, "johnmatava" <matavaj@s...> wrote:
      >
      > I live a urban area with a lot of noise and need an antenna for AM
      > broadcast and SWL. Short wave reception is useless with a long wire.
      > Thanks
      > John
      >
    • johnmatava
      Thanks for the good comments. I was using a couple of capacitors that I happened to have on hand. Probably should dig out something more realistic. As far as
      Message 2 of 11 , Jan 4, 2006
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        Thanks for the good comments. I was using a couple of capacitors
        that I happened to have on hand. Probably should dig out something
        more realistic.

        As far as the scope goes I was using a megaohm probe.




        --- In loopantennas@yahoogroups.com, "Stephen R. Yates" <aa5tb@y...>
        wrote:
        >
        > Hi John,
        >
        > Welcome to the list!
        >
        > First, your selection of capacitors is way too big. For that size
        > of a loop in the HF range the capacitor values will be measured in
        > pF, not uF.
        >
        > Second, the inner coupling loop transforms the impedance to 50 ohms
        > to match to the characteristic impedance of the feedline. Make
        sure
        > that the oscilloscope has a 50 ohm termination on it and you are
        not
        > using the normal > 1 megohm impedance.
        >
        > 73,
        > Steve - AA5TB
        >
        >
        >
        >
        >
        > http://www.aa5tb.com
        >
      • johnmatava
        Yeah it did help. I am trying to build a tuned loop. Probably should get a variable capactor from an old radio and play with that. Ultimately I would like to
        Message 3 of 11 , Jan 4, 2006
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          Yeah it did help. I am trying to build a tuned loop. Probably should
          get a variable capactor from an old radio and play with that.
          Ultimately I would like to

          --- In loopantennas@yahoogroups.com, "Rob Moore" <rmoore5@s...> wrote:
          >
          > John,
          >
          > Are you trying to build a broadband loop (untuned) or a tuned loop
          > (Uses a variable cap for tuning)? If you're building a broadband
          loop
          > it's best to connect to the loop directly through a roughly 4:1
          toroid
          > transformer to better match the impedances. The loop shold also not
          > have any gaps in it. (The Gap is typically put in a shield to
          prevent
          > the shield from acting like a shorted turn and absorbing all the
          signel.)
          >
          > If you're build a tuned loop, a variable capacitor goes in the gap
          and
          > you can use a sense loop or connect directly through a transformer.
          > If you're building a shielded tuned loop, the shield should have a
          > gap, centered in the shield, for the reasons described above.
          >
          > Hope this helps.
          >
          > Rob
          >
          > --- In loopantennas@yahoogroups.com, "johnmatava" <matavaj@s...>
          wrote:
          > >
          > > Group
          > >
          > > My first post to the group.
          > >
          > > I live a urban area with a lot of noise and need an antenna for
          AM
          > > broadcast and SWL. Short wave reception is useless with a long
          wire. I
          > > am trying to come up with a way of testing and understanding the
          > > resonate responce and gain of a loop antenna. Heres what I did;
          > >
          > > Set up a sine wave generator to a remote transmitter loop.
          > >
          > > Built a single turn external loop about 3' diameter with a gap of
          about
          > > 1/4" from 6 guage bare ground wire.
          > >
          > > Built a single turn interior loop about 6" diameter and hooked up
          to an
          > > oscilloscope. Made it from the same ground wire.
          > >
          > > The interior loop shows responce from the external source and a
          > > resonance at 8.6mHz. The responce is a nice sine wave at
          resonance and
          > > kind of broken below.
          > >
          > > There was a little change in maginitude with or without the
          external
          > > loop. Tried bridging the gap on the external loop with different
          caps
          > > and saw absolutely (yes absolutely) no differnce in gain. The
          resonate
          > > frequency stayed the same.
          > >
          > > Questions:
          > > Is there something fundimentally flawed with what I am doing?
          > > Is it possible I was actually seeing resonance from the
          transmitter
          > > loop when I did the sine sweep?
          > > Do the dimensions seem about right?
          > > I tried a number of caps from .1 to 1 microfarads. Is this about
          the
          > > right range?
          > >
          > > I am out of ideas for the time being. Any suggestions would
          help. I
          > > thought this was going to be straight forward.
          > >
          > > Thanks
          > > John
          > >
          >
        • johnmatava
          Thanks for the reply. You gave a good description of the setup. I should find some more realistic capacitors. I was surprised when bridging the gap made no
          Message 4 of 11 , Jan 4, 2006
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            Thanks for the reply. You gave a good description of the setup. I
            should find some more realistic capacitors. I was surprised when
            bridging the gap made no difference at all. Need to dig for some more
            realistic caps or maybe break open an old radio and use the tuner.

            --- In loopantennas@yahoogroups.com, Jim Dunstan <jimdunstan@r...>
            wrote:
            >
            > At 05:39 AM 03/01/2006 +0000, you wrote:
            > >Group
            > >
            > >My first post to the group.
            > >
            > >I live a urban area with a lot of noise and need an antenna for AM
            > >broadcast and SWL. Short wave reception is useless with a long
            wire. I
            > >am trying to come up with a way of testing and understanding the
            > >resonate responce and gain of a loop antenna. Heres what I did;
            > >
            > >Set up a sine wave generator to a remote transmitter loop.
            > >
            > >Built a single turn external loop about 3' diameter with a gap of
            about
            > >1/4" from 6 guage bare ground wire.
            > >
            > >Built a single turn interior loop about 6" diameter and hooked up
            to an
            > >oscilloscope. Made it from the same ground wire.
            > >
            > >The interior loop shows responce from the external source and a
            > >resonance at 8.6mHz. The responce is a nice sine wave at
            resonance and
            > >kind of broken below.
            > >
            > >There was a little change in maginitude with or without the
            external
            > >loop. Tried bridging the gap on the external loop with different
            caps
            > >and saw absolutely (yes absolutely) no differnce in gain. The
            resonate
            > >frequency stayed the same.
            > >
            > >Questions:
            > >Is there something fundimentally flawed with what I am doing?
            > >Is it possible I was actually seeing resonance from the transmitter
            > >loop when I did the sine sweep?
            > >Do the dimensions seem about right?
            > >I tried a number of caps from .1 to 1 microfarads. Is this about
            the
            > >right range?
            > >
            > >I am out of ideas for the time being. Any suggestions would
            help. I
            > >thought this was going to be straight forward.
            > >
            > >Thanks
            > >John
            >
            > Hi John,
            >
            > Let me see if I have it correct. You have 3 loops. Loop #1 is
            coupled to
            > a frequency source that is transmitting a signal across the HF
            > spectrum. Loop #2 is a 3 Ft diam. tuned receiving loop. Loop #3
            is 6 in
            > diam pickup loop mounted within Loop #2. You have an oscilloscope
            as the
            > receiver.
            >
            > You are doing nothing wrong given what you have said. The normal
            practice
            > is to tune the loop by putting a variable capacitor across the gap
            of the
            > 3' loop and placing the pickup loop at the opposite side of the 3'
            > loop. You are looking at capacitors in the micro microfarad
            range ... or
            > picofarad. If you put a standard 365 picofarad capacitor across
            the gap
            > you should be able to resonate the loop across much of the HF band.
            >
            > The fixed capacitor sizes you mention are much too large.
            >
            > Jim
            >
          • johnmatava
            Greg Looked at the website. Its real similar to what I want to do. I am sure it will help a lot. John ... in ...
            Message 5 of 11 , Jan 4, 2006
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              Greg

              Looked at the website. Its real similar to what I want to do.
              I am sure it will help a lot.

              John

              --- In loopantennas@yahoogroups.com, "Greg W:-)" <onegammyleg@y...>
              wrote:
              >
              > You might want to check out my small loop at
              > http://www.geocities.com/onegammyleg/ as I too live in a noise level
              > area that never drops below S 9+ on SW frequencies.
              > It is the only thing I have found that even comes close to working
              in
              > this QTH.
              >
              > regards
              >
              > gregW:-)
              >
              >
              ======================================================================
              ==
              >
              > --- In loopantennas@yahoogroups.com, "johnmatava" <matavaj@s...>
              wrote:
              > >
              > > I live a urban area with a lot of noise and need an antenna for
              AM
              > > broadcast and SWL. Short wave reception is useless with a long
              wire.
              > > Thanks
              > > John
              > >
              >
            • Greg W:-)
              John My setup works quite well and has been duplicated by many others which report similar performance to what I get. Nice an noise free , but dont be
              Message 6 of 11 , Jan 5, 2006
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                John

                My setup works quite well and has been duplicated by many others which
                report similar performance to what I get.

                Nice an noise free , but dont be expecting the sort of gain that a
                large loop or wire antenna can give and you will be pleased with the
                small loops performance.

                gregW:-)

                ========================================================================

                --- In loopantennas@yahoogroups.com, "johnmatava" <matavaj@s...> wrote:
                >
                > Greg
                >
                > Looked at the website. Its real similar to what I want to do.
                > I am sure it will help a lot.
                >
                > John
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