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Re: Image rejection problem with Ensemble RX II

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  • vbifyz
    The easiest test is to touch opamp inputs on the Softrock board with a screwdriver: one, than another, with the SDR software running. This will tell you
    Message 1 of 8 , Apr 1, 2012
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      The easiest test is to touch opamp inputs on the Softrock board with a screwdriver: one, than another, with the SDR software running. This will tell you whether both channels (from the mixer to the soundcard output to the software) are working without a gross imbalance.

      73, Mike

      --- In softrock40@yahoogroups.com, Robert Bajuk <rbajuk@...> wrote:
      >
      > TNX Stu... I/Q cable and audio connector on PCB is OK, already checked the
      > I/Q connection from the PCB (JP1) through the cable... Must be something on
      > the PCB, short or no connection
      >
      > Robert
      >
      > Dne 01. april 2012 21:28 je Stu Capon <powernumpty@...> napisal/-a:
      >
      > > **
      > >
      > >
      > > Hi Robert,
      > >
      > > No expert here but have been caught before.
      > > Start with daft things like audio plugs pushed fully home, those 3.5mm can
      > > be tricky to push fully if the PCB is open on desk.
      > > Obviously anything that shorts (or doesn't connect) second channel of the
      > > IQ does it.
      > >
      > > Stu
      > >
      > >
      > >
      > > On 01/04/12 20:14, Robert Bajuk wrote:
      > >
      > >
      > >
      > > Hello,
      > >
      > > I do own different Softrocks and all of them perform nice with my EMU 0202
      > >
      > > I have built RX II recently and all the test are OK but have problems with
      > > strong image on that one.
      > >
      > > Both sides are the same and I can not reject image within HDSDR or other
      > > software. Both signals are just the same and Channel Skew Calibration
      > > doesn't change anything, no changes at all. Other receivers work OK with
      > > the same soundcard settings and PC.
      > >
      > > As mentioned - all voltage tests are OK...
      > >
      > > Any suggestions where to start?
      > >
      > > 73 Robert
      > >
      > >
      > >
      > >
      >
    • Robert Bajuk
      Tnx Mike, tested opamp with the 10k resistor OK, touched opamp inputs pin 2 and 6 or R30 and R 30 and both of them are noticableon the S-meter on runing SDR
      Message 2 of 8 , Apr 2, 2012
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        Tnx Mike,

        tested opamp with the 10k resistor OK, touched opamp inputs pin 2 and 6 or R30 and R 30 and both of them are noticableon the S-meter on runing SDR sofware, but not the same. One goes for example from S7 to S8/9 and another one from S7 to S9 + 20db.

        Checked all over again, I have replaced AC74, transformers and still the same

        The other two Softrock work OK with the same setup (PC, cable, soundcard)

        Robert

        Dne 02. april 2012 02:09 je vbifyz <3ym3ym@...> napisal/-a:
         

        The easiest test is to touch opamp inputs on the Softrock board with a screwdriver: one, than another, with the SDR software running. This will tell you whether both channels (from the mixer to the soundcard output to the software) are working without a gross imbalance.

        73, Mike



        --- In softrock40@yahoogroups.com, Robert Bajuk <rbajuk@...> wrote:
        >
        > TNX Stu... I/Q cable and audio connector on PCB is OK, already checked the
        > I/Q connection from the PCB (JP1) through the cable... Must be something on
        > the PCB, short or no connection
        >
        > Robert
        >
        > Dne 01. april 2012 21:28 je Stu Capon <powernumpty@...> napisal/-a:
        >
        > > **

        > >
        > >
        > > Hi Robert,
        > >
        > > No expert here but have been caught before.
        > > Start with daft things like audio plugs pushed fully home, those 3.5mm can
        > > be tricky to push fully if the PCB is open on desk.
        > > Obviously anything that shorts (or doesn't connect) second channel of the
        > > IQ does it.
        > >
        > > Stu
        > >
        > >
        > >
        > > On 01/04/12 20:14, Robert Bajuk wrote:
        > >
        > >
        > >
        > > Hello,
        > >
        > > I do own different Softrocks and all of them perform nice with my EMU 0202
        > >
        > > I have built RX II recently and all the test are OK but have problems with
        > > strong image on that one.
        > >
        > > Both sides are the same and I can not reject image within HDSDR or other
        > > software. Both signals are just the same and Channel Skew Calibration
        > > doesn't change anything, no changes at all. Other receivers work OK with
        > > the same soundcard settings and PC.
        > >
        > > As mentioned - all voltage tests are OK...
        > >
        > > Any suggestions where to start?
        > >
        > > 73 Robert
        > >
        > >
        > >
        > >
        >


      • vbifyz
        If 2 channels are not the same, you will have image rejection problems. Check the feedback resistors of the opamp stage(without desoldering, only powered
        Message 3 of 8 , Apr 2, 2012
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          If 2 channels are not the same, you will have image rejection problems.
          Check the feedback resistors of the opamp stage(without desoldering, only powered down). Looks like there is 100 Ohm instead of 10 Ohm on one of the inputs, or 499 Ohm instead of 4.99k from output to input.

          73, Mike

          --- In softrock40@yahoogroups.com, Robert Bajuk <rbajuk@...> wrote:
          >
          > Tnx Mike,
          >
          > tested opamp with the 10k resistor OK, touched opamp inputs pin 2 and 6 or
          > R30 and R 30 and both of them are noticableon the S-meter on runing SDR
          > sofware, but not the same. One goes for example from S7 to S8/9 and another
          > one from S7 to S9 + 20db.
          >
          > Checked all over again, I have replaced AC74, transformers and still the
          > same
          >
          > The other two Softrock work OK with the same setup (PC, cable, soundcard)
          >
          > Robert
          >
        • Robert Bajuk
          TNX for suggestion / problem solved !! All four resistors you suggested + two 120 ohm resistors are OK but you made me think. I checked components after the
          Message 4 of 8 , Apr 3, 2012
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            TNX for suggestion / problem solved !! 

            All four resistors you suggested + two 120 ohm resistors are OK but you made me think. I checked components after the opamp - two  0.1 uF caps (C46 and C47) in series with the output line. C 46 was defective / interrupted, and yes, I have only one channel working. Replaced small SMD cap and viola, perfect image rejection now. Poison is always in small bottles:-)

            TNX & 73

            Robert

            Dne 03. april 2012 00:44 je vbifyz <3ym3ym@...> napisal/-a:
             

            If 2 channels are not the same, you will have image rejection problems.
            Check the feedback resistors of the opamp stage(without desoldering, only powered down). Looks like there is 100 Ohm instead of 10 Ohm on one of the inputs, or 499 Ohm instead of 4.99k from output to input.



            73, Mike

            --- In softrock40@yahoogroups.com, Robert Bajuk <rbajuk@...> wrote:
            >
            > Tnx Mike,
            >
            > tested opamp with the 10k resistor OK, touched opamp inputs pin 2 and 6 or
            > R30 and R 30 and both of them are noticableon the S-meter on runing SDR
            > sofware, but not the same. One goes for example from S7 to S8/9 and another
            > one from S7 to S9 + 20db.
            >
            > Checked all over again, I have replaced AC74, transformers and still the
            > same
            >
            > The other two Softrock work OK with the same setup (PC, cable, soundcard)
            >
            > Robert
            >


          • Bruce Tanner
            Message 5 of 8 , Apr 3, 2012
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              :-)

              On 4/3/2012 10:48 AM, Robert Bajuk wrote:  

              TNX for suggestion / problem solved !! 

              All four resistors you suggested + two 120 ohm resistors are OK but you made me think. I checked components after the opamp - two  0.1 uF caps (C46 and C47) in series with the output line. C 46 was defective / interrupted, and yes, I have only one channel working. Replaced small SMD cap and viola, perfect image rejection now. Poison is always in small bottles:-)

              TNX & 73

              Robert

              Dne 03. april 2012 00:44 je vbifyz <3ym3ym@...> napisal/-a:
               

              If 2 channels are not the same, you will have image rejection problems.
              Check the feedback resistors of the opamp stage(without desoldering, only powered down). Looks like there is 100 Ohm instead of 10 Ohm on one of the inputs, or 499 Ohm instead of 4.99k from output to input.



              73, Mike

              --- In softrock40@yahoogroups.com, Robert Bajuk <rbajuk@...> wrote:
              >
              > Tnx Mike,
              >
              > tested opamp with the 10k resistor OK, touched opamp inputs pin 2 and 6 or
              > R30 and R 30 and both of them are noticableon the S-meter on runing SDR
              > sofware, but not the same. One goes for example from S7 to S8/9 and another
              > one from S7 to S9 + 20db.
              >
              > Checked all over again, I have replaced AC74, transformers and still the
              > same
              >
              > The other two Softrock work OK with the same setup (PC, cable, soundcard)
              >
              > Robert
              >


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