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DDS-60 output

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  • dxradio33
    Folks, I have interfaced the DDS-60 to the V6 SR40 and it works fine with the exception of unwanted spurs. The problem looks to be too much gain from the
    Message 1 of 6 , May 14, 2006
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      Folks, I have interfaced the DDS-60 to the V6 SR40 and it works fine
      with the exception of unwanted spurs. The problem looks to be too
      much gain from the DDS-60. I am feeding the output of the DDS-60 to
      the base of Q2 through a 22pf cap. The output of the DDS-60 is just a
      tad over 3.8 v PP and I cannot get it down more than that. The
      crsytal ouput on the V6 is about 1.3 v PP. I have experimented with
      different values to provide more negative feedback for the AD8008 but
      to no avail (causes instability due to apparent decoupling issues) so
      it looks like the only route would be a rf pad using resistor
      combinations that I have virtually no access to (because of the
      values). Any other suggestions or success stories ? Thanks in advance.
      /joe
    • Jim Miller
      for pad values that you might have try some of the hamcalc programs. they allow you to do a design and then substitute values and see the consequences. if you
      Message 2 of 6 , May 14, 2006
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        for pad values that you might have try some of the hamcalc programs. they
        allow you to do a design and then substitute values and see the
        consequences.

        if you have any junque box at all you should be able to get there.

        good luck

        jim ab3cv
        ----- Original Message -----
        From: "dxradio33" <k8fc@...>
        To: <softrock40@yahoogroups.com>
        Sent: Sunday, May 14, 2006 11:16 AM
        Subject: [softrock40] DDS-60 output


        Folks, I have interfaced the DDS-60 to the V6 SR40 and it works fine
        with the exception of unwanted spurs. The problem looks to be too
        much gain from the DDS-60. I am feeding the output of the DDS-60 to
        the base of Q2 through a 22pf cap. The output of the DDS-60 is just a
        tad over 3.8 v PP and I cannot get it down more than that. The
        crsytal ouput on the V6 is about 1.3 v PP. I have experimented with
        different values to provide more negative feedback for the AD8008 but
        to no avail (causes instability due to apparent decoupling issues) so
        it looks like the only route would be a rf pad using resistor
        combinations that I have virtually no access to (because of the
        values). Any other suggestions or success stories ? Thanks in advance.
        /joe







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      • gw4gte
        use a smaller value coupling capacitor than 22pf, using the higher reactance to reduce the drive. Alternatively, add another cap to earth to form an ac
        Message 3 of 6 , May 14, 2006
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          use a smaller value coupling capacitor than 22pf, using the higher
          reactance to reduce the drive. Alternatively, add another cap to
          earth to form an ac potential divider.
          Dave
          --- In softrock40@yahoogroups.com, "dxradio33" <k8fc@...> wrote:
          >
          > Folks, I have interfaced the DDS-60 to the V6 SR40 and it works
          fine
          > with the exception of unwanted spurs. The problem looks to be too
          > much gain from the DDS-60. I am feeding the output of the DDS-60
          to
          > the base of Q2 through a 22pf cap. The output of the DDS-60 is
          just a
          > tad over 3.8 v PP and I cannot get it down more than that. The
          > crsytal ouput on the V6 is about 1.3 v PP. I have experimented
          with
          > different values to provide more negative feedback for the AD8008
          but
          > to no avail (causes instability due to apparent decoupling issues)
          so
          > it looks like the only route would be a rf pad using resistor
          > combinations that I have virtually no access to (because of the
          > values). Any other suggestions or success stories ? Thanks in
          advance.
          > /joe
          >
        • bob_wa6ufq
          Joe, To get the output of your DDS-60 down to the 1.3V level from its output of 3.8V would require approximately a 5 dB attenuator 1.3/3.8 = .342 10*log
          Message 4 of 6 , May 15, 2006
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            Joe,

            To get the output of your DDS-60 down to the 1.3V level from its
            output of 3.8V would require approximately a 5 dB attenuator
            1.3/3.8 = .342 10*log .342 = -4.65 dB

            The approximate resistor values for a 5 dB pad at 50 ohms are as follows:

            T-Pad: two 14 ohm resistors in series, with a 82 ohm resistor from the
            junction of the two resistors to ground (I'd use common values of 15
            ohms and 82 ohms).

            Pi-Pad: 178 ohms to ground on the input and output, with a 30 ohm
            resistor between the input and output ports.

            I'd probably go with the T-pad as the resistor values are more readily
            obtained.

            I assume that the 3.8 VPP was measured with the DDS-60's output turned
            down as far as you could get it. This approximate 5 dB attenuator will
            reduce the output to slightly less than the desired 1.3 VPP, so after
            you install the attenuator, just increase the DDS-60's output until
            you get the 1.3 VPP you need.

            Bob WA6UFQ




            --- In softrock40@yahoogroups.com, "dxradio33" <k8fc@...> wrote:
            >
            > Folks, I have interfaced the DDS-60 to the V6 SR40 and it works fine
            > with the exception of unwanted spurs. The problem looks to be too
            > much gain from the DDS-60. I am feeding the output of the DDS-60 to
            > the base of Q2 through a 22pf cap. The output of the DDS-60 is just a
            > tad over 3.8 v PP and I cannot get it down more than that. The
            > crsytal ouput on the V6 is about 1.3 v PP. I have experimented with
            > different values to provide more negative feedback for the AD8008 but
            > to no avail (causes instability due to apparent decoupling issues) so
            > it looks like the only route would be a rf pad using resistor
            > combinations that I have virtually no access to (because of the
            > values). Any other suggestions or success stories ? Thanks in advance.
            > /joe
            >
          • kd5byb
            Good evening all, I hate to dig up old information, but I want to query the group. Is the method below (feeding base of Q2 thru a cap) the preferred way of
            Message 5 of 6 , Jul 2, 2006
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              Good evening all,

              I hate to dig up old information, but I want to query the group. Is
              the method below (feeding base of Q2 thru a cap) the preferred way of
              injecting external VFO's or DDS' to the SR V6?

              I noted in the files area that folks are using external VFO's/DDS' but
              didn't see a schematic that noted the input arrangement.

              Thanks and 73,
              Ben, KD5BYB

              --- In softrock40@yahoogroups.com, "dxradio33" <k8fc@...> wrote:
              >
              > Folks, I have interfaced the DDS-60 to the V6 SR40 and it works fine
              > with the exception of unwanted spurs. The problem looks to be too
              > much gain from the DDS-60. I am feeding the output of the DDS-60 to
              > the base of Q2 through a 22pf cap.
            • Jarmo Blomster
              ... I just replaced the crystal with DDS60 output. This gives me a possibility to use either a crystal or DDS60. It s not beautiful but it works. //jarmo
              Message 6 of 6 , Jul 3, 2006
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                > I noted in the files area that folks are using external VFO's/DDS' but
                > didn't see a schematic that noted the input arrangement.
                I just replaced the crystal with DDS60 output. This gives me a possibility to
                use either a crystal or DDS60. It's not beautiful but it works.

                //jarmo oh8kva
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