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QSD vs Dual Mixers

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  • Bill Meahan K8QN
    Something has been puzzling me: OTHER THAN COST, is there any inherent benefit to using a QSD, like the SoftRock or FlexRadio instead of two conventional
    Message 1 of 5 , Aug 31, 2007
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      Something has been puzzling me:

      OTHER THAN COST, is there any inherent benefit to using a QSD, like
      the SoftRock or FlexRadio instead of two "conventional" mixers with
      their LO inputs fed in phase quadrature, like the KK7B R2 design?

      Seems to me like a pair of H-mode mixers (such as Gian mentioned in
      his earlier post to this group:
      http://groups.yahoo.com/group/softrock40/message/13940) driven by
      either two AD9912's locked in quadrature or an AD9912 driving the
      appropriate flip-flops would make One Damn Fine SDR! :-) :-)

      Of course this would cost quite a bit more than a SoftRock, no
      question about that, but given the wide frequency range over which it
      could operate and the essentially "bullet-proof" front end provided by
      the H-mode mixers, wouldn't it be worth it?

      73 de K8QN
      "An old Ham, but an SDR novice"
    • k5nwa
      ... Nothing to be puzzled about, the SoftRock is geared towards low cost, but there are many ways to skin a cat as they say. All you need is two receivers with
      Message 2 of 5 , Aug 31, 2007
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        At 01:12 PM 8/31/2007, you wrote:

        >Something has been puzzling me:
        >
        >OTHER THAN COST, is there any inherent benefit to using a QSD, like
        >the SoftRock or FlexRadio instead of two "conventional" mixers with
        >their LO inputs fed in phase quadrature, like the KK7B R2 design?
        >
        >Seems to me like a pair of H-mode mixers (such as Gian mentioned in
        >his earlier post to this group:
        ><http://groups.yahoo.com/group/softrock40/message/13940>http://groups.yahoo.com/group/softrock40/message/13940)
        >driven by
        >either two AD9912's locked in quadrature or an AD9912 driving the
        >appropriate flip-flops would make One Damn Fine SDR! :-) :-)
        >
        >Of course this would cost quite a bit more than a SoftRock, no
        >question about that, but given the wide frequency range over which it
        >could operate and the essentially "bullet-proof" front end provided by
        >the H-mode mixers, wouldn't it be worth it?
        >
        >73 de K8QN
        >"An old Ham, but an SDR novice"
        >

        Nothing to be puzzled about, the SoftRock is geared towards low cost,
        but there are many ways to skin a cat as they say. All you need is
        two receivers with identical gain with their LO in Quadrature.

        Your idea would work out quite well I would think. You could even use
        two Gilbert Cell Mixers like the SA612 which cost a buck and are good
        to two meters if one is interested in low cost. Two inexpensive
        Mini-Circuits DBDM would work quite well out to 500MHz, 5HGz if you
        buy the right ones.


        Cecil
        KD5NWA
        www.softrockradio.org www.qrpradio.com

        "Blessed are the cracked, for they shall let in the light."
      • Bill Meahan K8QN
        ... Low cost, yes, good IIP3 performance? Not so hot. Pretty poor, actually! :-) :-) ... Yup. That s exactly the KK7B R2 approach. ... Or in the corporate
        Message 3 of 5 , Aug 31, 2007
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          --- In softrock40@yahoogroups.com, k5nwa <k5nwa@...> wrote:


          > Your idea would work out quite well I would think. You could even use
          > two Gilbert Cell Mixers like the SA612 which cost a buck and are good
          > to two meters if one is interested in low cost.

          Low cost, yes, good IIP3 performance? Not so hot. Pretty poor,
          actually! :-) :-)


          > Two inexpensive
          > Mini-Circuits DBDM would work quite well out to 500MHz, 5HGz if you
          > buy the right ones.
          >

          Yup. That's exactly the KK7B R2 approach.

          >
          > Cecil
          > KD5NWA
          > www.softrockradio.org www.qrpradio.com
          >
          > "Blessed are the cracked, for they shall let in the light."
          >

          Or in the corporate world: "Blessed are those who go around in the
          right circles, for they shall become big wheels."

          73 de K8QN
        • k5nwa
          ... If you are trying to build a contest radio with two SA612 s then maybe we can do some business together, you see I have this bridge in Brooklyn for sale at
          Message 4 of 5 , Aug 31, 2007
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            At 05:00 PM 8/31/2007, you wrote:
            > > Two inexpensive
            > > Mini-Circuits DBDM would work quite well out to 500MHz, 5HGz if you
            > > buy the right ones.
            > >
            >
            >Yup. That's exactly the KK7B R2 approach.
            >
            > >
            > > Cecil
            > > KD5NWA
            > > www.softrockradio.org www.qrpradio.com
            > >
            > > "Blessed are the cracked, for they shall let in the light."
            > >
            >
            >Or in the corporate world: "Blessed are those who go around in the
            >right circles, for they shall become big wheels."
            >
            >73 de K8QN
            >

            If you are trying to build a contest radio with two SA612's then
            maybe we can do some business together, you see I have this bridge in
            Brooklyn for sale at a really good price, and maybe you could charge
            people to go across and make enough money to pay for the bridge in a
            year or so.

            I will also steal your signature and add it to my collection, so
            there sue me! :-P



            Cecil
            KD5NWA
            www.softrockradio.org www.qrpradio.com

            "Blessed are the cracked, for they shall let in the light."
          • Bill Dumke
            Cecil, Actually I believe the Intermod performance of the switch IC s used in the softRock is limited by the dynamic range of the sound card, not the switches.
            Message 5 of 5 , Aug 31, 2007
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              Cecil,

              Actually I believe the Intermod performance of the switch IC's used in
              the softRock is limited by the dynamic range of the sound card, not the
              switches.

              If we can't get good enough noise performance with the switches at 28
              MHz, it might be well worth it to use SA612's at 10 meters. It would
              eliminate the need for the two flip flops. Maybe that commercial phase
              splitter recently talked about could be used for the quadrature at any
              HF band.

              If a preamp is going to have to be used at 10 meters for HF reception
              for the switches, that will also directly hurt the intermod performance
              even if it is a perfectly linear amplifier as well. So that would have
              to be taken into consideration as well in doing the comparison.

              I wonder if anyone has done an analysis to see if the SA612's which have
              better noise figure and some gain instead of the switch's loss would
              still be limited by the sound card in terms of intermodulation
              performance? If that is true, then it might be worth it. Of course op
              amp gains, etc. would have to be lowered, or maybe even eliminated.

              Bill wa9pwr

              k5nwa wrote:
              > At 05:00 PM 8/31/2007, you wrote:
              >
              >>> Two inexpensive
              >>> Mini-Circuits DBDM would work quite well out to 500MHz, 5HGz if you
              >>> buy the right ones.
              >>>
              >>>
              >> Yup. That's exactly the KK7B R2 approach.
              >>
              >>
              >>> Cecil
              >>> KD5NWA
              >>> www.softrockradio.org www.qrpradio.com
              >>>
              >>> "Blessed are the cracked, for they shall let in the light."
              >>>
              >>>
              >> Or in the corporate world: "Blessed are those who go around in the
              >> right circles, for they shall become big wheels."
              >>
              >> 73 de K8QN
              >>
              >>
              >
              > If you are trying to build a contest radio with two SA612's then
              > maybe we can do some business together, you see I have this bridge in
              > Brooklyn for sale at a really good price, and maybe you could charge
              > people to go across and make enough money to pay for the bridge in a
              > year or so.
              >
              > I will also steal your signature and add it to my collection, so
              > there sue me! :-P
              >
              >
              >
              > Cecil
              > KD5NWA
              > www.softrockradio.org www.qrpradio.com
              >
              > "Blessed are the cracked, for they shall let in the light."
              >
              >
              >
              >
              > Yahoo! Groups Links
              >
              >
              >
              >
              >
              >
              >
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