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Re: G4HOL Loop details

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  • Lee Moore (Gimbert)
    Not if a ferrite ring coupling transformer is used ... Regards. Lee ... G6ZSG.
    Message 1 of 4 , May 12, 2009
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      Not if a ferrite ring coupling transformer is used ...

      Regards.

      Lee ... G6ZSG.


      --- In loopantennas@yahoogroups.com, M HOLDEN <mholden909@...> wrote:
      >
      > My golden rules: Avoid the use of coax cable as an H.F. loop feeder. (It will unbalance the system and could therefore produce unwanted received noise [ QRN ] )
      >                        The formula 1005/f(MHz) is good from hf through to uhf. This will be the total length of a full wave loop in Feet.
      >                        Use medium impedance twin like 300Wslotted if you are going to make one loop work on multiple frequencies, as most of the time the "seen" impedance at the loop feedpoint will also be "medium". The system will remain in balance and therefore reject QRN.
      >                        When using a single band full wave loop antenna, the best match to a 50Wtransceiver will be a quarter wave or an odd number of multiple quarter waves of 75 / 80Wpolythene twin. Do not ignore the manufacturer's Velocity Factor of the cable. A VF of say 90% will mean that the feeder length will be 90% of a quarter wave long. Read up and understand the use of quarter wave line impedance transformation. The 234 divided by f (MHz) will give a true quarter wave of copper wire, in Feet.  If you make a good 40 metre loop it should work well on 15 metres too.
      >                        A current balun at the antenna tuner end of the feeder may not be needed as it could be transforming already low impedances even lower and beyond the range of some tuners capabilities.
      > I enclose my optimised HF loop design as well as a 2lvhf design which will work well on the lowest budget and with dual polarity.
      > The Cebik website will go into greater depths, but there is enough here to wet the appetite. 
      > Mike G4HOL 
      >
      > [Non-text portions of this message have been removed]
      >
    • M HOLDEN
      Thanks for that Lee. When you have a simple monoband antenna your solution is sound. When you change frequencies on a multiband loop, you also see large
      Message 2 of 4 , May 12, 2009
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        Thanks for that Lee. When you have a simple monoband antenna your solution is sound. When you change frequencies on a multiband loop, you also see large changes in feedpoint impedances. These are in the range of "medium" impedance, and 300 ohm or 450 ohm ladder feeder is far better equipped for that than coax at 50 or 75 ohms. I experimented some years ago with a 150Ft loop using a ferrite ring coupling. I was not too impressed with the heat generated in the ferrite. I know of others who have used the loop on auto tuners at the feedpoint, (and have dispensed with the ladder line) and had great results on 50 ohm cable running back to the rig in the shack. I am sorry that my omega signs and lambdas became W and l in the print up earlier, as this must have caused some confusion. Best wishes, Mike G4HOL




        ________________________________
        From: Lee Moore (Gimbert) <leemoore500@...>
        To: loopantennas@yahoogroups.com
        Sent: Tuesday, 12 May, 2009 9:31:01 AM
        Subject: [loopantennas] Re: G4HOL Loop details





        Not if a ferrite ring coupling transformer is used ...

        Regards.

        Lee ... G6ZSG.

        --- In loopantennas@ yahoogroups. com, M HOLDEN <mholden909@ ...> wrote:
        >
        > My golden rules: Avoid the use of coax cable as an H.F. loop feeder. (It will unbalance the system and could therefore produce unwanted received noise [ QRN ] )
        >                        The formula 1005/f(MHz) is good from hf through to uhf. This will be the total length of a full wave loop in Feet.
        >                        Use medium impedance twin like 300Wslotted if you are going to make one loop work on multiple frequencies, as most of the time the "seen" impedance at the loop feedpoint will also be "medium". The system will remain in balance and therefore reject QRN.
        >                        When using a single band full wave loop antenna, the best match to a 50Wtransceiver will be a quarter wave or an odd number of multiple quarter waves of 75 / 80Wpolythene twin. Do not ignore the manufacturer' s Velocity Factor of the cable. A VF of say 90% will mean that the feeder length will be 90% of a quarter wave long. Read up and understand the use of quarter wave line impedance transformation.  The 234 divided by f (MHz) will give a true quarter wave of copper wire, in Feet.  If you make a good 40 metre loop it should work well on 15 metres too.
        >                        A current balun at the antenna tuner end of the feeder may not be needed as it could be transforming already low impedances even lower and beyond the range of some tuners capabilities.
        > I enclose my optimised HF loop design as well as a 2lvhf design which will work well on the lowest budget and with dual polarity.
        > The Cebik website will go into greater depths, but there is enough here to wet the appetite. 
        > Mike G4HOL 
        >
        > [Non-text portions of this message have been removed]
        >




        [Non-text portions of this message have been removed]
      • jrtow3rd@bellsouth.net
        ... One problem folks learned many moons ago with balanced feeders was that whether sized/spaced for 300, 450, 0r 600 Ohms characteristic impedance was
        Message 3 of 4 , May 14, 2009
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          --- In loopantennas@yahoogroups.com, M HOLDEN <mholden909@...> wrote:
          >
          > Thanks for that Lee. When you have a simple monoband antenna your solution is sound. When you change frequencies on a multiband loop, you also see large changes in feedpoint impedances. These are in the range of "medium" impedance, and 300 ohm or 450 ohm ladder feeder is far better equipped for that than coax at 50 or 75 ohms. I experimented some years ago with a 150Ft loop using a ferrite ring coupling. I was not too impressed with the heat generated in the ferrite. I know of others who have used the loop on auto tuners at the feedpoint, (and have dispensed with the ladder line) and had great results on 50 ohm cable running back to the rig in the shack. I am sorry that my omega signs and lambdas became W and l in the print up earlier, as this must have caused some confusion. Best wishes, Mike G4HOL
          >
          >
          One problem folks learned many moons ago with balanced feeders was that whether sized/spaced for 300, 450, 0r 600 Ohms characteristic impedance was unimportant if the load (aerial) did not match that impedance. Sure, a well thought out balanced tuner could 'match' a pair of bed springs fed with ladder line - or so a VSWR bridge in the coax feed would indicate. The feedline would be part of the load, in the mismatched aerial case, and radiation would commence 'in the shack'. On receive, some signal pickup would occur on the feedline, too. The benefit of the matching ferrite toroidal transformer at the loop's feedpoint is that the coax feed, even with a non-negligible VSWR, is still well-shielded. Also, the Hi-Z winding can be split - with a grounded CT to keep from developing static charges on the loop.

          Before 1972, the Marine Band in the USA ran from 2-3 MHz AM. Since then, it has been VHF NBFM - around the NOAA/Marine WX frequencies. Small craft that needed communications in the latter years used a transceiver, often with a single 12V filament sweep tube PA plate modulated by a solid state audio amp, running 30-50W RF. The 'channels' were significantly apart, frequency-wise, and the output Pi-network was adjusted, ie, tapped, for each channel - and the length of 'feedline' (insulated wire) and height of the mast could not be altered for fear of detuning the transmitter. Touching it while it was in use could result in an RF burn, too. Designed 'RF in the shack' - but I digress..John
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