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Active Antenna Amplifiers

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  • Chris Trask
    Over the holidays, I took a great deal of time to investigate some ideas that I had with regard to the design of lossless feedback amplifiers in an effort to
    Message 1 of 8 , Jan 2, 2008
      Over the holidays, I took a great deal of time to investigate some ideas
      that I had with regard to the design of lossless feedback amplifiers in an
      effort to improve the dynamic range of active antennas, both in terms of
      noise figure (NF) and distortion (IMD products). I had quite a bit of
      success, and wrote a monologue about some of what I did:

      http://www.home.earthlink.net/~christrask/Lossless%20Feedback%20Amplifiers.p
      df

      The details of all this, plus some other advanced techniques, are part of a
      full article that I'm presently writing.

      Chris

      ,----------------------. High Performance Mixers and
      / What's all this \ Amplifiers for RF Communications
      / extinct stuff, anyhow? /
      \ _______,--------------' Chris Trask / N7ZWY
      _ |/ Principal Engineer
      oo\ Sonoran Radio Research
      (__)\ _ P.O. Box 25240
      \ \ .' `. Tempe, Arizona 85285-5240
      \ \ / \
      \ '" \ IEEE Senior Member #40274515
      . ( ) \
      '-| )__| :. \ Email: christrask@...
      | | | | \ '. http://www.home.earthlink.net/~christrask
      c__; c__; '-..'>.__

      Graphics by Loek Frederiks
    • Chris Trask
      Lately there has been a good deal of discussion about the overall performance of active antenna amplifiers, and now that the number of postings has decreased I
      Message 2 of 8 , Jan 20, 2013
        Lately there has been a good deal of discussion about the overall performance of active antenna amplifiers, and now that the number of postings has decreased I felt it was a good time to bring up an issue pertaining to the overall discussion.

        In general, the overall quality of an active antenna amplifier encompasses the intermodulation distortion (IMD) and noise figure (NF) performance. For the vast majority of transistors, you can have one or the other but very rarely both simultaneously. To be specific, good NF performance is usually obtained at low collector (or drain) currents, while good IMD performance requires substantially higher currents, resulting in higher NF.

        NF is a result of two distinct noise mechanisms, being thermal (Nyquist) and 1/f (shot) noise. The first of these is wideband noise that is generally of low spectral density. The second, however, is low-frequency noise that becomes noticable at frequencies below 100kHz to 1MHz and which increases with lower frequency. You might think that 1/f noise is of no consequence at HF frequencies and higher, however it modulates the bias current, which in turn modulates the inband signals in the same manner that SSB phase noise on local oscillator (LO) signals results in reciprocal mixing.

        One method that has been reduced to practice to overcome the high NF of high frequency devices is to use a low-noise audio transistor to detect the low-frequency noise at the emitter, amplify and invert it, then couple it to the base. Ulrich Rohde introduced the method for reducing the SSB phase noise of microwave oscillators, while at the same time I employed it for reducing the NF and even-order distortion in common-base and lossless feedback amplifiers.

        I have not seen anyone making use of this method for active antenna amplifiers, yet is is a method that has been reduced to practice for some time. This seems to be a good moment to remind the designer community of this so that we can see some new applications and an advancement in the art of designing active antenna amplifiers.


        Chris
      • Paul V Birke PEng
        clever stuff Chris we have very low noise op amps as well for the audio range with ultralow distortion LME49720 best Paul ________________________________
        Message 3 of 8 , Jan 20, 2013
          clever stuff Chris

          we have very low noise op amps as well for the audio range with ultralow distortion

          LME49720

          best Paul



          From: Chris Trask <christrask@...>
          To: Loop Antennas <loopantennas@yahoogroups.com>
          Sent: Sunday, January 20, 2013 10:07:45 AM
          Subject: [loopantennas] Active Antenna Amplifiers

           
          Lately there has been a good deal of discussion about the overall performance of active antenna amplifiers, and now that the number of postings has decreased I felt it was a good time to bring up an issue pertaining to the overall discussion.

          In general, the overall quality of an active antenna amplifier encompasses the intermodulation distortion (IMD) and noise figure (NF) performance. For the vast majority of transistors, you can have one or the other but very rarely both simultaneously. To be specific, good NF performance is usually obtained at low collector (or drain) currents, while good IMD performance requires substantially higher currents, resulting in higher NF.

          NF is a result of two distinct noise mechanisms, being thermal (Nyquist) and 1/f (shot) noise. The first of these is wideband noise that is generally of low spectral density. The second, however, is low-frequency noise that becomes noticable at frequencies below 100kHz to 1MHz and which increases with lower frequency. You might think that 1/f noise is of no consequence at HF frequencies and higher, however it modulates the bias current, which in turn modulates the inband signals in the same manner that SSB phase noise on local oscillator (LO) signals results in reciprocal mixing.

          One method that has been reduced to practice to overcome the high NF of high frequency devices is to use a low-noise audio transistor to detect the low-frequency noise at the emitter, amplify and invert it, then couple it to the base. Ulrich Rohde introduced the method for reducing the SSB phase noise of microwave oscillators, while at the same time I employed it for reducing the NF and even-order distortion in common-base and lossless feedback amplifiers.

          I have not seen anyone making use of this method for active antenna amplifiers, yet is is a method that has been reduced to practice for some time. This seems to be a good moment to remind the designer community of this so that we can see some new applications and an advancement in the art of designing active antenna amplifiers.

          Chris


        • Paul V Birke PEng
          makes you wonder why IF stages at 455 kHz are not designed with the audio transistor inversion trick!! best Paul ________________________________ From: Chris
          Message 4 of 8 , Jan 20, 2013
            makes you wonder why IF stages at 455 kHz are not designed with the audio transistor inversion trick!!

            best Paul


            From: Chris Trask <christrask@...>
            To: Loop Antennas <loopantennas@yahoogroups.com>
            Sent: Sunday, January 20, 2013 10:07:45 AM
            Subject: [loopantennas] Active Antenna Amplifiers

             
            Lately there has been a good deal of discussion about the overall performance of active antenna amplifiers, and now that the number of postings has decreased I felt it was a good time to bring up an issue pertaining to the overall discussion.

            In general, the overall quality of an active antenna amplifier encompasses the intermodulation distortion (IMD) and noise figure (NF) performance. For the vast majority of transistors, you can have one or the other but very rarely both simultaneously. To be specific, good NF performance is usually obtained at low collector (or drain) currents, while good IMD performance requires substantially higher currents, resulting in higher NF.

            NF is a result of two distinct noise mechanisms, being thermal (Nyquist) and 1/f (shot) noise. The first of these is wideband noise that is generally of low spectral density. The second, however, is low-frequency noise that becomes noticable at frequencies below 100kHz to 1MHz and which increases with lower frequency. You might think that 1/f noise is of no consequence at HF frequencies and higher, however it modulates the bias current, which in turn modulates the inband signals in the same manner that SSB phase noise on local oscillator (LO) signals results in reciprocal mixing.

            One method that has been reduced to practice to overcome the high NF of high frequency devices is to use a low-noise audio transistor to detect the low-frequency noise at the emitter, amplify and invert it, then couple it to the base. Ulrich Rohde introduced the method for reducing the SSB phase noise of microwave oscillators, while at the same time I employed it for reducing the NF and even-order distortion in common-base and lossless feedback amplifiers.

            I have not seen anyone making use of this method for active antenna amplifiers, yet is is a method that has been reduced to practice for some time. This seems to be a good moment to remind the designer community of this so that we can see some new applications and an advancement in the art of designing active antenna amplifiers.

            Chris


          • ik1wvq
            Hi, what is your opinion about the use of OPERATIONAL AMPLIFIERS as AD8009 or OPA847, declared low noise and high IMD ?? I tried a single OPA847 inverting
            Message 5 of 8 , Jan 21, 2013
              Hi,
              what is your opinion about the use of OPERATIONAL AMPLIFIERS as
              AD8009 or OPA847, declared low noise and high IMD ??

              I tried a single OPA847 inverting amplifier configuration with 10 ohm Rg and 1 Kohm Rf (loop conncted to Rg via a 2uF multilayer capacitor)..
              This seems to work, but I do not have sufficient instrumentation for measuring noise and IMD, nor a standard loop to compare with mine.

              thanks to all.

              best regard

              Mauro IK1WVQ



              --- In loopantennas@yahoogroups.com, "Chris Trask" wrote:
              >
              > Over the holidays, I took a great deal of time to investigate some ideas
              > that I had with regard to the design of lossless feedback amplifiers in an
              > effort to improve the dynamic range of active antennas, both in terms of
              > noise figure (NF) and distortion (IMD products). I had quite a bit of
              > success, and wrote a monologue about some of what I did:
              >
              > http://www.home.earthlink.net/~christrask/Lossless%20Feedback%20Amplifiers.p
              > df
              >
              > The details of all this, plus some other advanced techniques, are part of a
              > full article that I'm presently writing.
              >
              > Chris
              >
              > ,----------------------. High Performance Mixers and
              > / What's all this \ Amplifiers for RF Communications
              > / extinct stuff, anyhow? /
              > \ _______,--------------' Chris Trask / N7ZWY
              > _ |/ Principal Engineer
              > oo\ Sonoran Radio Research
              > (__)\ _ P.O. Box 25240
              > \ \ .' `. Tempe, Arizona 85285-5240
              > \ \ / \
              > \ '" \ IEEE Senior Member #40274515
              > . ( ) \
              > '-| )__| :. \ Email: christrask@...
              > | | | | \ '. http://www.home.earthlink.net/~christrask
              > c__; c__; '-..'>.__
              >
              > Graphics by Loek Frederiks
              >
            • ik1wvq
              Hi, what is your opinion about the use of a operational amplifier like AD8009 or OPA847, declaring low NF and high IMD ??? I am trying a single inverting
              Message 6 of 8 , Jan 21, 2013
                Hi,
                what is your opinion about the use of a operational amplifier like AD8009 or OPA847, declaring low NF and high IMD ???

                I am trying a single inverting amplifier configuration (10 ohm Rg, 1 kohm Rf, single turn loop connected to Rg via a 2uF multilayer chip) with a OPA847.

                this seems to work, but I do not have sufficient instrumentation to made serious measurements of NF and IMD..

                Many thanks ..
                best regards to all.

                Mauro IK1WVQ
              • dx11
                Just FYI I know of two loop designs with the OP847, they can be seen at: http://wl1030.pa3ang.nl/content/ ( This one is in English. You need to register here
                Message 7 of 8 , Jan 22, 2013
                  Just FYI I know of two loop designs with the OP847, they can be seen at:

                  http://wl1030.pa3ang.nl/content/ ( This one is in English. You need to
                  register here to get access, but that no other consequences)


                  http://dijkjj.home.xs4all.nl/download/bqc-wl1030xx.pdf (This one is in
                  Dutch, but with lots of pictures, so you will understand anyway).

                  Cor Beijersbergen
                • ik1wvq
                  many thanks Cor, the WL1030 project is very interesting, but this is the only one (what I know) using this approach ... thanks again regards Mauro IK1WVQ
                  Message 8 of 8 , Jan 22, 2013
                    many thanks Cor,
                    the WL1030 project is very interesting, but this is the only one (what I know) using this approach ...

                    thanks again

                    regards
                    Mauro IK1WVQ





                    --- In loopantennas@yahoogroups.com, "dx11" wrote:
                    >
                    > Just FYI I know of two loop designs with the OP847, they can be seen at:
                    >
                    > http://wl1030.pa3ang.nl/content/ ( This one is in English. You need to
                    > register here to get access, but that no other consequences)
                    >
                    >
                    > http://dijkjj.home.xs4all.nl/download/bqc-wl1030xx.pdf (This one is in
                    > Dutch, but with lots of pictures, so you will understand anyway).
                    >
                    > Cor Beijersbergen
                    >
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