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Re: [softrock40] non linear SSB PA, [WOT]

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  • Dan Andersson
    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,
    Message 1 of 8 , Mar 1 3:00 PM
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      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@...
    • DSNman@comcast.net
      Test please ignore! -- Loren Moline WA7SKT ... From: Dan Andersson ... Art, Of course it s going to work. We do this for microwave
      Message 2 of 8 , Mar 1 3:03 PM
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        Test please ignore!

        --
        Loren Moline
        WA7SKT

        -------------- Original message ----------------------
        From: Dan Andersson <dan@...>
        > 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@...
        >
      • Phil Harman
        Hi Art, Your theory is sound but there will be a problem feeding the signal envelope back into the sound card due to the inherent delays in the signal
        Message 3 of 8 , Mar 1 3:55 PM
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          Hi Art,

          Your theory is sound but there will be a problem feeding the signal envelope
          back into the sound card due to the inherent delays in the signal
          processing.

          Over on the HPSDR project we are designing an exciter that has the features
          you defined. Rather than using a soundcard/PC we will do the processing in
          an FPGA. Have a look at the block diagram of Penelope at

          < http://hpsdr.org/wiki/index.php?title=PENELOPE >

          As a 1/2w exciter Penelope is intended to drive either a conventional liner
          PA or a non linear PA (Class D/E/F) by providing the relevant phase
          modulated RF and envelope signals.

          73's Phil.... VK6APH




          ----- Original Message -----
          From: "Art" <KY1K@...>
          To: <softrock40@yahoogroups.com>
          Sent: Friday, March 02, 2007 6:01 AM
          Subject: [softrock40] non linear SSB PA, [WOT]


          > 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
          >
          >
          >
          >
          >
          > Yahoo! Groups Links
          >
          >
          >
          >
          >
          >
          > --
          > No virus found in this incoming message.
          > Checked by AVG Free Edition.
          > Version: 7.5.446 / Virus Database: 268.18.5/706 - Release Date: 2/28/2007
          > 4:09 PM
          >
          >
        • 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 4 of 8 , Mar 1 10:53 PM
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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 5 of 8 , Mar 1 11:21 PM
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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 6 of 8 , Mar 2 12:15 AM
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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 7 of 8 , Mar 2 1:03 AM
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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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