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3480Re: RF Systems DX-One Pro MkII - Bi-Loop or not ?

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  • Fraser
    May 14, 2007
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      --- In loopantennas@yahoogroups.com, "Steve Ratzlaff"
      <steveratz@...> wrote:
      >
      > Hi,
      > I'm familiar with the circuits used in the head end of the older
      DX-1 Pro,
      > and the receiver coupler/supply.
      > The head end is a basic high-impedance active whip antenna. The
      circuit is
      > an exact clone of the old Ralph Burhans circuit he published back
      in the
      > 1980's, using 100% negative feedback.
      (SNIPPED)


      Hi Steve,

      Many thanks for that superb description of the DX-1. You have made
      my day as I have been scratching my head about this antennas design
      for ages.

      When I X-Rayed the mast section it had four wires interconnecting
      the various 'loop' arms but I couldn't be sure how they were
      connected. They certainly are not all wired in parallel in the MKII.
      I was wondering if they had wired the 'loop' arms in series to
      effectively compress a long whip into a small space. This bit of the
      design still eludes me.

      As for the amplifier... your information is invaluable. The MKII
      amplifier is stated as providing 10dB gain whereas the MKI was
      spec'ed at 6dB gain. The issue of input capacitance is very
      interesting indeed. I have some NOS Motorola high power jFETs (or
      tFETS ?) that were used in some Watkins Johnson amplifiers that I
      maintained. I suspect that these will also exhibit higher than
      desirable input capacitance so I will re think using them in any
      antenna designs that I build.

      Thank you for your excellent help with this question Steve. It does,
      however, lead me to wonder about RF Systems performance claims. RFS
      make the MLB1 and this has caused much discussion both positive and
      negative. I like their AA-150 that was built for the Lowe HF-150 but
      it may be no better than any other active whip on the market. It is
      well built though. The DX-10 is basically an AA-150 in a different
      shell. As for the passive HF magnetic whips and some of their other
      exotic designs, I am not sure that these are not just well
      engineered 'snake oil' antennas. I own an RF Systems DX-500 which is
      beautifully constructed and claims to work upto 500 MHz. I have
      found that it needs an excellent groundplane for HF work and is
      really just an RF probe (it has an extremely short active element).

      Oh well.... it looks like the DX-1 is just an exotic & expensive
      active whip pretending to be a loop then :-(

      Thanks to everyone for their input on this topic. I'm off to start
      saving for a Wellbrook ALA1530+.

      Fraser
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