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Re: [loopantennas] Re: Active loop amplifier

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  • Chris Trask
    ... goal ... I ve read ... to the ... amplifier ... response ... application ... No, reducing the input impedance has absolutely nothing to do with high
    Message 1 of 8 , Jun 30, 2010
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      >
      > I understand that this requires proper analysis, but in my case the design
      goal
      > is not only the wide dynamic range, but the deep null as well. From what
      I've read
      > so far, this requires the loop to be "ideally magnetic", i.e. insensitive
      to the
      > electrical field. This is achieved by using Alford loops, or reducing the
      amplifier
      > input impedance, or both.
      >
      > Reducing the input impedance requires high open-loop gain and flat phase
      response
      > of the amplifier. I think opamps can be better for this particular
      application
      > (deep null), but again, detailed analysis is required.
      >

      No, reducing the input impedance has absolutely nothing to do with high
      open-loop gain. I achieve exceptionally low input impedances with
      common-base amplifiers using a very simple technique that I patented:

      http://www.home.earthlink.net/~christrask/MWSCAS99.pdf

      "Common Base Amplifier Linearization Using Augmentation," RF Design,
      October 1999, pp. 30-34.

      "High Efficiency Broadband Linear Push-Pull Power Amplifiers Using
      Linearity Augmentation," Proceedings of the 2002 International Symposium
      on Circuits and Systems (ISCAS 2002), 28 May 2002, Phoenix, Arizona,
      Vol. 2, pp. 432-435.

      Common-Base Amplifiers with Linearity Augmentation, US Patent 6,271,721,
      7 August 2001.

      And it will outperform your monolithic devices any day of the week.

      Chris Trask
      N7ZWY / WDX3HLB
      Senior Member IEEE
      http://www.home.earthlink.net/~christrask/
    • Vahe ohanian
      Hello Chris With your experience  should the board be Through Hole design or surface mount Would the Through hole make a difference  in RF ? I checked quick
      Message 2 of 8 , Jul 21, 2010
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        Hello Chris

        With your experience  should the board be Through Hole design or surface mount

        Would the Through hole make a difference  in RF ?

        I checked quick and MPS6521SM  seems not to be available but I did not spend too
        much time


        I will go with through hole design for now since that would be the easiest to
        make and provide as a kit .. for most.


        Vahe



         



        ________________________________
        From: Chris Trask <christrask@...>
        To: loopantennas@yahoogroups.com; loopantennas@yahoogroups.com
        Sent: Wed, June 30, 2010 8:41:26 AM
        Subject: Re: [loopantennas] Active loop amplifier

         

        >
        > I'm going to try and assemble something like this:
        >http://www.lz1aq.signacor.com/docs/wsml/wideband-active-sm-loop-antenna.htm
        > Anybody tried a different amplifier for such loop? I've found a
        > nice opamp from Intersil, EL2125 that has amazingly low voltage
        > noise and enough bandwidth. Ordered samples today.
        > Any experience here with this or similar parts?
        >

        I'm in the process of designing an amplifier similar to this that should have
        better noise and IMD performance. The progress of this has been hampered by
        other obligations. I'm using this project as a basis for the mechanical design
        of shielded loops and Moebius Strip loops.

        Avoid using opamps for active antenna design. Despite their low noise and
        distortion specs, they still do not compare with those of discrete devices.

        Chris Trask
        N7ZWY / WDX3HLB
        Senior Member IEEE
        http://www.home.earthlink.net/~christrask/






        [Non-text portions of this message have been removed]
      • Chris Trask
        ... mount ... I ve used both. The transformers, connector, 47uF capacitor, and transistors (plus a snall 10-turn pot used for R5) are all through hole.
        Message 3 of 8 , Jul 21, 2010
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          >
          > With your experience should the board be Through Hole design or surface
          mount
          >

          I've used both. The transformers, connector, 47uF capacitor, and
          transistors (plus a snall 10-turn pot used for R5) are all through hole.
          Everything else is surface mount. There's little to be gained in the way of
          board space going from a TO-92 to SOT-23 transistor package. There is,
          however, much to be gained using 1206 capacitors and resistors. I did this
          in order to get the best cost and performance. There is also a specific
          need for this to fit inside an electrical conduit fitting, which is far
          cheaper and stronger than an electrical utility box.

          >
          > Would the Through hole make a difference in RF ?
          >

          Not for HF and below.

          >
          > I checked quick and MPS6521SM seems not to be available but I did not
          spend
          > too much time
          >

          Another reason for using through hole for that part.

          Chris
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