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Re: [loopantennas] Re: Antenna amplifier link

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  • Paul Birke
    thanks so much JR for this Paul ... A couple of tips Keep the layout symetrical as possible Match your resistors within .1% and you don t need the ten turn
    Message 1 of 16 , Apr 29, 2006
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      thanks so much JR for this

      Paul

      --- jr_dakota <SG2112@...> wrote:


      ---------------------------------
      A couple of tips

      Keep the layout symetrical as possible

      Match your resistors within .1% and you don't need the
      ten turn trim
      pot (You'll still use a fixed resistor there) unless
      you are really picky

      If your primary interest is above 2Mhz use a #43
      cores, if it's below
      2Mhz use a #75 or a 'J' cores

      Pay real close attention to phasing of all the
      transformers, one out
      of whack with throw the whole circuit off, possibly to
      the point of
      making it a relatively high powered VHF oscillator

      I also use a slightly different biasing scheme, I use
      different
      resistors at the base to set my current and keep a
      fixed 51 ohm
      resistor on the input/emitter to get a better 50 ohm
      input/output
      impedance match ... basically my biasing values are
      the same as this
      in my SDR http://www.qrp.pops.net/preamp.htm (bottom
      of page)

      Unless you need a balanced circuit (an untuned loop
      for example)
      and/or have a REALLY strong mixer (A +17 DBM or a
      Tayloe Detector)
      following it, you'd probably be as well or better off
      with a single
      transistor Norton amp ... it's also an advantage to
      use the push-pull
      setup for Direct Conversion because of the inherent
      2nd harmonic
      cancellation

      JR

      --- In loopantennas@yahoogroups.com, Paul Birke
      <nonlinear@...> wrote:
      >
      > very good JR
      >
      > thanks
      >
      > Paul
      >
      > any enhancements on Dallas' orginal article?
      > any further hints?
      > Dan's Part for the transistors I guess.
      >
      > Paul
      >
      >
      > --- jr_dakota <SG2112@...> wrote:
      >
      >
      > ---------------------------------
      > Yes, I'm using one in a SDR front end and have
      another
      > partially built
      > for a Wellbrook loop clone I'm working on .... They
      > are so bullet
      > proof you could put a full watt of power into them
      and
      > they'll hardly
      > burp .... the inherent 2nd harmonic cancellation
      (just
      > like a push
      > pull audio power amps) makes them especially
      > attractive in Direct
      > Conversion designs where IP2 is more important than
      > IP3 ... it's also
      > an excellent match to the Tayloe/QSD detector which
      > has an
      > outrageously high IP3 for a mixer so you need a
      preamp
      > with an
      > outrageously high IP3 so as not to degrade
      performance
      > ... this baby
      > is it .... there is also a similar design by Jacob
      > Makhinson, N6NWP
      > but it uses a bipolar supply for biasing and
      grounded
      > bases by the
      > slight performance increase isn't worth the hassle
      in
      > my opinion ...
      > then again I usually have a bipolar supply in most
      of
      > my designs for
      > audio frequency circuits (a bipolar supply opamp
      will
      > beat a single
      > supply in noise and power supply rejection every
      time)
      > so then it
      > wouldn't be a big deal
      >
      > JR
      >
      > --- In loopantennas@yahoogroups.com, Paul Birke
      > <nonlinear@> wrote:
      > >
      > >
      > >
      > >
      > > Found a bunch of 2N5109's for the Norton CBTF amps
      > > that the Lankford
      > > article describes, but haven't had a chance to
      > build
      > > one for LF yet.
      > >
      > > hi Joe et al
      > >
      > >
      > > Has anyone in the group built and tried out these
      > > amps?
      > >
      > > Paul
      > >
      >
      >
      >
      >
      >
      >
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      If you've got links, post them in the Links section!
      http://groups.yahoo.com/group/loopantennas/links

      Post files here. If the file comes from a website,
      please put it in the Links rather than uploading the
      file.
      http://groups.yahoo.com/group/loopantennas/files

      You can now view images at higher resolution in
      Photos. Upload JPG and GIF into Photos. Please convert
      BMP or TIF to JPG or GIF before uploading.
      http://ph.groups.yahoo.com/group/loopantennas/photos

      And please trim all this when replying!



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