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Re: non linear SSB PA, [WOT]

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  • tom_iphi
    You can even buy an SSB PA which works in class E based on this idea: http://www.sgcworld.com/500watt.html Linear transponders in satellites also use this
    Message 1 of 8 , Mar 1, 2007
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      You can even buy an SSB PA which works in class E based on this idea:
      http://www.sgcworld.com/500watt.html

      Linear transponders in satellites also use this method to conserve
      energy.

      73 Tom DG8SAQ

      --- In softrock40@yahoogroups.com, Dan Andersson <dan@...> wrote:
      >
      > On Thursday 01 March 2007 21:01:39 Art wrote:
      > > Greetings all,
      > >
      > > I've recently become interested in using non linear amplifiers to
      > > amplify SSB. Obviously, this is a problem, we all know an
      amplifier
      > > for SSB has to be linear, or class AB1.
      > >
      > > Even if we bias an AB1 amp properly, some (all) power amps have
      non
      > > linear responses. Even if we put the cleanest audio on the planet
      > > into them, they don't work well. We refer to this problem with
      many
      > > different technical terms. But, the problem is non-linearity in
      the
      > > PA itself. Whenever the output of a PA is distorted, it uses more
      > > spectrum than it should and causes interference well outside it's
      > > expected bandwidth.
      > >
      > > The short version is that the amplifiers output doesn't follow
      the input.
      > >
      > > But, what about using a sound card to correct this issue? If we
      feed
      > > soundcard audio to a PA and measure (or characterize) it's input
      vs
      > > output, can we then use that data to modify the audio supplied to
      the
      > > PA using the soundcard? In this manner, we would be
      > > 'predistorting' the input audio intentionally, but doing it in
      such
      > > a manner as to make the PA respond with proper output.
      > >
      > > I know this might sound radical, and no one would want run a
      computer
      > > just for the purpose of doing this. But, many of us already use
      the
      > > computer soundcard to generate transmit audio anyway, so the real
      > > cost of implementing this sort of change means some extra software
      > > and some additional processor utilization.
      > >
      > > What we might get in return might be a way to use a class B (or C)
      > > amp as an SSB PA, and it would sound clean and not splatter.
      > > Depending on how well it works, we might even be able to use a
      class
      > > D or E PA for SSB, efficiencies of 90 percent are possible in
      class D/E.
      > >
      > > I wonder if anyone else has considered this? I sure would like to
      be
      > > able to use my 4CX250 amp on ssb without having my neighbors
      complain
      > > that my signal was 'wide'.
      > >
      > > Regards,
      > >
      > > Art
      >
      >
      > Art,
      >
      > Of course it's going to work.
      >
      > We do this for microwave applications where we have a wide
      bandwidth demand on
      > the aerials. we compensate based on the known "weak points" and we
      are also
      > actively compensating other unlinearities.
      >
      > Regarding the PA unlinearity, this is one of the reasons we use
      DSP's more and
      > more frequently.
      >
      > However! You can only compensate for known unlinearities. If your
      PA changes
      > behaviours depending on load and SWR, the you need to add a control
      mechanism
      > and a monitoring receiver to linearise your output.
      >
      > It's also a bit easier to compensate for this with SDR as the
      signal can be
      > treated before it reaches the PA. But again, it's the signal at the
      end of
      > the PA that is the main problem.
      >
      > But brought to a conclusion, yes, it's done today on commercial and
      mil
      > radios. It takes a lot of umpf to do for us hams but why not...
      >
      >
      > //Dan
      >
      >
      >
      > --
      > Dan Andersson, M0DFI
      > dan@...
      >
    • RAY
      ... From: tom_iphi You can even buy an SSB PA which works in class E based on this idea: http://www.sgcworld.com/500watt.html
      Message 2 of 8 , Mar 1, 2007
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        ----- Original Message -----
        From: tom_iphi
        You can even buy an SSB PA which works in class E based on this idea:
        http://www.sgcworld.com/500watt.html
        *************************************************
        The company has a identified what they call a mechanical weakness in
        connectors and
        will not deliver the product till this is resolved. They are also working
        on a self-contained 20M single band only.

        It should be a great product if they get the mechanical thing resolved.

        Please don't shoot the messenger. I want this as bad as anyone else

        73,Ray, N0FY
      • cesco12342000
        ... The solution is EER (Envelope Elimination and Restoration). One problem with soundcard realization of EER is that the Envelope must be a DC coupled signal.
        Message 3 of 8 , Mar 2, 2007
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          > What we might get in return might be a way to use a class B (or C)
          > amp as an SSB PA, and it would sound clean and not splatter.

          The solution is EER (Envelope Elimination and Restoration).

          One problem with soundcard realization of EER is that the Envelope must
          be a DC coupled signal. Normal soundcards wont do that. You will need a
          "patched" soundcard, or a dedicated hardware, or...

          A solution is to modulate the Envelope signal onto an AM carrier, send
          it out of the soundcard and demodulate it there. The AM frequency would
          be 24khz, the modulation band going from DC to more than 3khz.

          For the softrock this means two audio channels IQ phase signal, + one
          audio channel for the E signal. Since we all got those 5.1 soundcards by
          now, it IS possible to do !
        • richard
          ... Yes it possible but its asking for trouble in Ham land, I ve worked on amplifiers that reduce distortion, by prediction the effect a non-linear PA
          Message 4 of 8 , Mar 2, 2007
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            Art wrote:
            >
            > Greetings all,
            >
            > I've recently become interested in using non linear amplifiers to
            > amplify SSB. Obviously, this is a problem, we all know an amplifier
            > for SSB has to be linear, or class AB1.
            >
            > Even if we bias an AB1 amp properly, some (all) power amps have non
            > linear responses. Even if we put the cleanest audio on the planet
            > into them, they don't work well. We refer to this problem with many
            > different technical terms. But, the problem is non-linearity in the
            > PA itself. Whenever the output of a PA is distorted, it uses more
            > spectrum than it should and causes interference well outside it's
            > expected bandwidth.
            >
            > The short version is that the amplifiers output doesn't follow the input.
            >

















            <snip>

            Yes it possible but its asking for trouble in Ham land, I've worked on
            amplifiers that
            reduce distortion, by prediction the effect a non-linear PA has,
            intermod, transients etc,
            and correcting phase and amplitude before it fed to the PA.
            Its not a technology I feel would be easy to use on Ham applications,
            Using it for edge and similar
            modes maybe, but SSB is push the limits hard. you can predict and alter
            a signal when you know the exact pattern
            ,speech is much harder


            Richard
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