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Unbalance With Antenna Connected ???

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  • n3hkn
    Using Rocky to view unbalance. Softrock-5 80M. With no antenna, or a dummy load, Rocky shows very close balance +- 2dbfs. If I connect the antenna (GAP
    Message 1 of 7 , Oct 2, 2006
      Using Rocky to view unbalance. Softrock-5 80M.

      With no antenna, or a dummy load, Rocky shows very close balance +-
      2dbfs.

      If I connect the antenna (GAP Challenger) The unbalance jumps to
      10dbfs. I use the same antenna with Softrock 5's and 6's on 40m and 20m
      with good balance. "Playing" with the antenna tuner does not change the
      unbalance. ?????????

      Dick N3HKN
    • Marco
      Hi all, I performed some more tests on IMD and dynamic range of the SoftRock V6 (original and modified). Here is a summary of the results. For all
      Message 2 of 7 , Oct 2, 2006
        Hi all,

        I performed some more tests on IMD and dynamic range of the SoftRock V6 (original and modified). Here is a summary of the results.
        For all measurements, the reference bandwidth is 2.4kHz, the signal spacing is 15kHz and the frequency is around 7050kHz.

        Instuments used: two HP 8640B signal generators, HP 8494A and -B step attenuators, Olektron power combiner. Levels checked with an HP 8566B spectrum analyzer. Power bandwidths and S/N measured with a Fluke 8920A digital RMS voltmeter. All instruments have traceable calibration.

        1) Unmodified SoftRock, Soundblaster USB 16bit audio interface (16bit, 48kHz, better antialiasing and response than the usual AC97 found in PCs)
        MDS: -105dBm
        blocking dynamic range: 96dB
        IMD3 dynamic range: not measurable (blocking occurs by saturation of the audio interface)
        IIP3: -

        2) same as (1), soundcard Audiophile 192 (24bit, sampling at 96kHz)
        MDS: -110dBm
        Blocking dynamic range: 100dB
        IMD3 dynamic range: 93dB
        IIP3: +29dBm

        3) same as (2), post-mixer amp voltage gain reduced from 500 times (5kOhm/10Ohm resistors on the opamp) to 90 times (900Ohm/10Ohm)
        MDS: -110dBm
        Blocking dynamic range: 110dB
        IMD3 dynamic range: 96dB
        IIP3: +34dBm

        4) same as (2), post-mixer amplifier has been replaced by a couple of OP27G powered from +/-12V. Opamp gain is now 200 times (2kOhm/10Ohm)
        MDS: -110dBm
        Blocking dynamic range: 115dB
        IMD3 dynamic range: 102dB
        IIP3: +43dBm

        My comments:

        a) I don't see any saturation in the FST3253 at least up to +10dBm (not checked over that)
        b) the IMD products seem to come mainly from the opamp and audio interface. Low power, low voltage opamps are the limit here
        c) some front-end gain is advisable to raise the MDS and stabilize the impedance seen by the mixer, if the opamp and audio interface can handle the strong signals. Noise from the opamp dominates the noise floor, of course; measured noise figure here is approx. 30dB
        d) IIP3 figures appear very good, but the real performance is limited by the poor image suppression and the 2nd order audio harmonic generation in the chain. With only two tones at the input the spectrum becomes a real forest, such that it's difficult to find a clean spot to see the IMD products. So, probably we have to talk about SFDR (spurious free dynamic range) or the system. Much harder than a simple IMD3 measurement.

        Next step: to test different mixer topologies (switch followed by an active integrator, as proposed on the HPSDR group, and some other ideas).

        73 - Marco IK1ODO
      • Phil Covington
        ... ideas). ... Hi Marco, Very interesting results. I will be particularly interested in your measurements of an active integrator version. 73 de Phil N8VB
        Message 3 of 7 , Oct 2, 2006
          --- In softrock40@yahoogroups.com, Marco <ik1odo@...> wrote:
          >
          > Hi all,
          >
          > I performed some more tests on IMD and dynamic range of the SoftRock
          > V6 (original and modified). Here is a summary of the results.
          > For all measurements, the reference bandwidth is 2.4kHz, the signal
          > spacing is 15kHz and the frequency is around 7050kHz.
          >
          > Instuments used: two HP 8640B signal generators, HP 8494A and -B step
          > attenuators, Olektron power combiner. Levels checked with an HP 8566B
          > spectrum analyzer. Power bandwidths and S/N measured with a Fluke
          > 8920A digital RMS voltmeter. All instruments have traceable calibration.
          >
          > 1) Unmodified SoftRock, Soundblaster USB 16bit audio interface
          > (16bit, 48kHz, better antialiasing and response than the usual AC97
          > found in PCs)
          > MDS: -105dBm
          > blocking dynamic range: 96dB
          > IMD3 dynamic range: not measurable (blocking occurs by saturation of
          > the audio interface)
          > IIP3: -
          >
          > 2) same as (1), soundcard Audiophile 192 (24bit, sampling at 96kHz)
          > MDS: -110dBm
          > Blocking dynamic range: 100dB
          > IMD3 dynamic range: 93dB
          > IIP3: +29dBm
          >
          > 3) same as (2), post-mixer amp voltage gain reduced from 500 times
          > (5kOhm/10Ohm resistors on the opamp) to 90 times (900Ohm/10Ohm)
          > MDS: -110dBm
          > Blocking dynamic range: 110dB
          > IMD3 dynamic range: 96dB
          > IIP3: +34dBm
          >
          > 4) same as (2), post-mixer amplifier has been replaced by a couple of
          > OP27G powered from +/-12V. Opamp gain is now 200 times (2kOhm/10Ohm)
          > MDS: -110dBm
          > Blocking dynamic range: 115dB
          > IMD3 dynamic range: 102dB
          > IIP3: +43dBm
          >
          > My comments:
          >
          > a) I don't see any saturation in the FST3253 at least up to +10dBm
          > (not checked over that)
          > b) the IMD products seem to come mainly from the opamp and audio
          > interface. Low power, low voltage opamps are the limit here
          > c) some front-end gain is advisable to raise the MDS and stabilize
          > the impedance seen by the mixer, if the opamp and audio interface can
          > handle the strong signals. Noise from the opamp dominates the noise
          > floor, of course; measured noise figure here is approx. 30dB
          > d) IIP3 figures appear very good, but the real performance is limited
          > by the poor image suppression and the 2nd order audio harmonic
          > generation in the chain. With only two tones at the input the
          > spectrum becomes a real forest, such that it's difficult to find a
          > clean spot to see the IMD products. So, probably we have to talk
          > about SFDR (spurious free dynamic range) or the system. Much harder
          > than a simple IMD3 measurement.
          >
          > Next step: to test different mixer topologies (switch followed by an
          > active integrator, as proposed on the HPSDR group, and some other
          ideas).
          >
          > 73 - Marco IK1ODO
          >


          Hi Marco,

          Very interesting results. I will be particularly interested in your
          measurements of an active integrator version.

          73 de Phil N8VB
        • FRANCIS CARCIA
          I also measured 96 dB dynamic range with my sdr board using a FST3253. At 2.5 KHz spacing 84 dB.My 3 dB MDS was a bit lower using INA163s I was also using a
          Message 4 of 7 , Oct 2, 2006
            I also measured 96 dB dynamic range with my sdr board using a FST3253. At 2.5 KHz spacing 84 dB.My 3 dB MDS was a bit lower using INA163s I was also using a stock sound card. My generators were also a pair of 8640Bs Frank wa1gfz

            Phil Covington <p.covington@...> wrote:
            --- In softrock40@yahoogro ups.com, Marco <ik1odo@...> wrote:
            >
            > Hi all,
            >
            > I performed some more tests on IMD and dynamic range of the SoftRock
            > V6 (original and modified). Here is a summary of the results.
            > For all measurements, the reference bandwidth is 2.4kHz, the signal
            > spacing is 15kHz and the frequency is around 7050kHz.
            >
            > Instuments used: two HP 8640B signal generators, HP 8494A and -B step
            > attenuators, Olektron power combiner. Levels checked with an HP 8566B
            > spectrum analyzer. Power bandwidths and S/N measured with a Fluke
            > 8920A digital RMS voltmeter. All instruments have traceable calibration.
            >
            > 1) Unmodified SoftRock, Soundblaster USB 16bit audio interface
            > (16bit, 48kHz, better antialiasing and response than the usual AC97
            > found in PCs)
            > MDS: -105dBm
            > blocking dynamic range: 96dB
            > IMD3 dynamic range: not measurable (blocking occurs by saturation of
            > the audio interface)
            > IIP3: -
            >
            > 2) same as (1), soundcard Audiophile 192 (24bit, sampling at 96kHz)
            > MDS: -110dBm
            > Blocking dynamic range: 100dB
            > IMD3 dynamic range: 93dB
            > IIP3: +29dBm
            >
            > 3) same as (2), post-mixer amp voltage gain reduced from 500 times
            > (5kOhm/10Ohm resistors on the opamp) to 90 times (900Ohm/10Ohm)
            > MDS: -110dBm
            > Blocking dynamic range: 110dB
            > IMD3 dynamic range: 96dB
            > IIP3: +34dBm
            >
            > 4) same as (2), post-mixer amplifier has been replaced by a couple of
            > OP27G powered from +/-12V. Opamp gain is now 200 times (2kOhm/10Ohm)
            > MDS: -110dBm
            > Blocking dynamic range: 115dB
            > IMD3 dynamic range: 102dB
            > IIP3: +43dBm
            >
            > My comments:
            >
            > a) I don't see any saturation in the FST3253 at least up to +10dBm
            > (not checked over that)
            > b) the IMD products seem to come mainly from the opamp and audio
            > interface. Low power, low voltage opamps are the limit here
            > c) some front-end gain is advisable to raise the MDS and stabilize
            > the impedance seen by the mixer, if the opamp and audio interface can
            > handle the strong signals. Noise from the opamp dominates the noise
            > floor, of course; measured noise figure here is approx. 30dB
            > d) IIP3 figures appear very good, but the real performance is limited
            > by the poor image suppression and the 2nd order audio harmonic
            > generation in the chain. With only two tones at the input the
            > spectrum becomes a real forest, such that it's difficult to find a
            > clean spot to see the IMD products. So, probably we have to talk
            > about SFDR (spurious free dynamic range) or the system. Much harder
            > than a simple IMD3 measurement.
            >
            > Next step: to test different mixer topologies (switch followed by an
            > active integrator, as proposed on the HPSDR group, and some other
            ideas).
            >
            > 73 - Marco IK1ODO
            >

            Hi Marco,

            Very interesting results. I will be particularly interested in your
            measurements of an active integrator version.

            73 de Phil N8VB


          • pvharman@arach.net.au
            Hi Marco, Thanks for your most interesting measurements. When you test the ISQ (switch followed by an active integrator) note that the switch is closed for 90
            Message 5 of 7 , Oct 2, 2006
              Hi Marco,

              Thanks for your most interesting measurements. When you test the ISQ (switch
              followed by an active integrator) note that the switch is closed for 90
              degrees. This provides the lowest conversion loss.

              I too have found the limitation due to the second harmonic distortion of the
              audio amplifiers. It seems that a push pull amplifier made from discrete
              components will cure this although it would be nice to find an IC that has the
              same performance.

              73's Phil...VK6APH
            • Marco
              ... Hi Phil, I ordered a couple of AD797. Expensive things, approx $5 in 1000 s but €12 each from distributors... I will do some test. As far as I know it is
              Message 6 of 7 , Oct 3, 2006
                At 02.16 03/10/2006, you wrote:

                >Hi Marco,
                >
                >Thanks for your most interesting measurements. When you test the ISQ (switch
                >followed by an active integrator) note that the switch is closed for 90
                >degrees. This provides the lowest conversion loss.
                >
                >I too have found the limitation due to the second harmonic distortion of the
                >audio amplifiers. It seems that a push pull amplifier made from discrete
                >components will cure this although it would be nice to find an IC
                >that has the
                >same performance.
                >
                >73's Phil...VK6APH

                Hi Phil,

                I ordered a couple of AD797. Expensive things, approx $5 in 1000's
                but €12 each from distributors... I will do some test. As far as I
                know it is the opamp having the lower ratio between En and In at the
                input. I hope that the distortion will be good too.

                Anyone is aware of commercial opamps with less than 1nV/rtHz of En?

                73 - Marco IK1ODO
              • Marco
                ... Will do. I m too busy this week, but possibly by the next weekend... 73 - Marco
                Message 7 of 7 , Oct 3, 2006
                  At 22.22 02/10/2006, you wrote:


                  >Hi Marco,
                  >
                  >Very interesting results. I will be particularly interested in your
                  >measurements of an active integrator version.
                  >
                  >73 de Phil N8VB

                  Will do. I'm too busy this week, but possibly by the next weekend...

                  73 - Marco
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