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Re: [softrock40] SoftRock40 Lite ... a bit deaf

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  • Tony Parks
    Hi Tom, The SoftRock Lite RX should have a sensitivity of about -110 dBm if working properly. If you have a calibrated source this is easy to checked.
    Message 1 of 9 , Apr 30, 2007
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      Hi Tom,
       
      The SoftRock Lite RX should have a sensitivity of about -110 dBm if working properly.  If you have a calibrated source this is easy to checked.  Listening tests require a 50 ohm antenna connected between the ANT IN-RTN plated through holes at the edge of the board near the crystal.  (The antenna return connection is isolated from the circuit ground by the transformer T1.)
       
      Other problems on the circuit board that can result in low sensitivity include bad solder joints at L1 and T1.  Also if the secondary windings of T1 are not connected properly there can be a 40 dB sensitivity loss.  Please see the builder's note for information on proper connection of T1.  Another quick check to to make sure the op-amp U5 is not saturated by checking the voltage on pins 1 and 7 referenced to circuit ground.  These two voltages should be about 2.5 VDC.
       
      73,
      Tony KB9YIG
      ----- Original Message -----
      Sent: Monday, April 30, 2007 4:21 AM
      Subject: [softrock40] SoftRock40 Lite ... a bit deaf

      Hello All ...

      I'm new to this group and everything SDR so I know you'll go easy on me!

      I've built an SR40 Lite kit and it is definitely receiving but quite
      deaf. I can say that it's deaf because I've compared it to another one
      that a friend of mine built, and there's a bit output difference
      between them.

      Since I can hear faint transmissions, and due to the board having been
      checked out in detail by myself and someone else for potential errors
      (none found,) I turned to the schematic to see where to go next. I see
      U4 and U5 as being in the frame for further investigation but I'm
      unsure how to check these chips out.

      So the situation is that I need guidance in starting down the road of
      probing the board and isolating the fault; can anyone help please?

      Thanks in advance for your expertise and time.

      ... Tom.

    • natsystems
      Hi Tony ... thanks for your reply. I m afraid I don t have equipment that would allow me to measure the receiver sensitivity, all I have is a good multimeter
      Message 2 of 9 , May 1, 2007
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        Hi Tony ... thanks for your reply.

        I'm afraid I don't have equipment that would allow me to measure the
        receiver sensitivity, all I have is a good multimeter and an old'ish
        oscilloscope.

        I measured the voltages at pins 1 & 7 of U5 and they are both 2.5v

        I then measured the input side of U5 on pins 2 & 6 and these are
        sitting at 2.5v DC. I would have thought I should have seen some form
        of pulse signal on these pins?

        Pin 14 of U4 seems to have the right clock pulse on it at 7.056 Mhz
        (got this from the OSD timing diagram in the softrock-40 assembly and
        operating manual v1)

        Can you suggest other signals to check please?

        Cheers .... Tom.



        --- In softrock40@yahoogroups.com, "Tony Parks" <raparks@...> wrote:
        >
        > Hi Tom,
        >
        > The SoftRock Lite RX should have a sensitivity of about -110 dBm if
        working properly. If you have a calibrated source this is easy to
        checked. Listening tests require a 50 ohm antenna connected between
        the ANT IN-RTN plated through holes at the edge of the board near the
        crystal. (The antenna return connection is isolated from the circuit
        ground by the transformer T1.)
        >
        > Other problems on the circuit board that can result in low
        sensitivity include bad solder joints at L1 and T1. Also if the
        secondary windings of T1 are not connected properly there can be a 40
        dB sensitivity loss. Please see the builder's note for information
        on proper connection of T1. Another quick check to to make sure the
        op-amp U5 is not saturated by checking the voltage on pins 1 and 7
        referenced to circuit ground. These two voltages should be about 2.5
        VDC.
        >
        > 73,
        > Tony KB9YIG
        > ----- Original Message -----
        > From: natsystems
        > To: softrock40@yahoogroups.com
        > Sent: Monday, April 30, 2007 4:21 AM
        > Subject: [softrock40] SoftRock40 Lite ... a bit deaf
        >
        >
        > Hello All ...
        >
        > I'm new to this group and everything SDR so I know you'll go easy
        on me!
        >
        > I've built an SR40 Lite kit and it is definitely receiving but
        quite
        > deaf. I can say that it's deaf because I've compared it to
        another one
        > that a friend of mine built, and there's a bit output difference
        > between them.
        >
        > Since I can hear faint transmissions, and due to the board having
        been
        > checked out in detail by myself and someone else for potential
        errors
        > (none found,) I turned to the schematic to see where to go next.
        I see
        > U4 and U5 as being in the frame for further investigation but I'm
        > unsure how to check these chips out.
        >
        > So the situation is that I need guidance in starting down the
        road of
        > probing the board and isolating the fault; can anyone help please?
        >
        > Thanks in advance for your expertise and time.
        >
        > ... Tom.
        >
      • Chris Albertson
        ... I also have an old scope too that is worthless as a measurement device. Calibration is off by more than 10X. and all the traces run down hill. You can
        Message 3 of 9 , May 1, 2007
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          --- natsystems <tom@...> wrote:

          > Hi Tony ... thanks for your reply.
          >
          > I'm afraid I don't have equipment that would allow me to measure the
          > receiver sensitivity, all I have is a good multimeter and an old'ish
          > oscilloscope.

          I also have an old scope too that is worthless as a measurement device.
          Calibration is off by more than 10X. and all the traces run down hill.

          You can build an RF voltmeter for about a buck.
          http://www.io.com/~n5fc/rfprobe1.htm
          The trouble is the diode detector is not linear. The one
          below uses a matched diode to compensate for the detector.
          http://www.kk5na.com/kk5na_files/AccupManual.htm



          Chris Albertson
          Home: 310-376-1029 chrisalbertson90278@...
          Office: 310-336-5189 Christopher.J.Albertson@...

          __________________________________________________
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        • natsystems
          Thanks Chris ... I m a great believer in home-brew gear. The kk5na website design looks intersting and I ll probably look into that one as I build up my
          Message 4 of 9 , May 1, 2007
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            Thanks Chris ... I'm a great believer in home-brew gear. The kk5na
            website design looks intersting and I'll probably look into that one
            as I build up my amateur radio test gear again after a very long break
            away.

            All the best ... Tom GM4DOZ

            --- In softrock40@yahoogroups.com, Chris Albertson
            <chrisalbertson90278@...> wrote:
            >
            >
            > --- natsystems <tom@...> wrote:
            >
            > > Hi Tony ... thanks for your reply.
            > >
            > > I'm afraid I don't have equipment that would allow me to measure the
            > > receiver sensitivity, all I have is a good multimeter and an old'ish
            > > oscilloscope.
            >
            > I also have an old scope too that is worthless as a measurement device.
            > Calibration is off by more than 10X. and all the traces run down hill.
            >
            > You can build an RF voltmeter for about a buck.
            > http://www.io.com/~n5fc/rfprobe1.htm
            > The trouble is the diode detector is not linear. The one
            > below uses a matched diode to compensate for the detector.
            > http://www.kk5na.com/kk5na_files/AccupManual.htm
            >
            >
            >
            > Chris Albertson
            > Home: 310-376-1029 chrisalbertson90278@...
            > Office: 310-336-5189 Christopher.J.Albertson@...
            >
            > __________________________________________________
            > Do You Yahoo!?
            > Tired of spam? Yahoo! Mail has the best spam protection around
            > http://mail.yahoo.com
            >
          • Len Warner
            ... Tell us what sort of pulse signal you were expecting and we may be able to tell you whether you should (or more likely, should not) be seeing it.
            Message 5 of 9 , May 2, 2007
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              At 09:20 07/05/02, [softrock40] Digest Number 1723 wrote:
              > Posted by: "natsystems" tom@... natsystems
              > Date: Tue May 1, 2007 9:52 am ((PDT))
              >[snip]
              >
              >I then measured the input side of U5 on pins 2 & 6 and these are
              >sitting at 2.5v DC. I would have thought I should have seen some form
              >of pulse signal on these pins?

              Tell us what sort of "pulse signal" you were expecting and we may
              be able to tell you whether you should (or more likely, should not)
              be seeing it.

              Otherwise, it is difficult to fathom what your reasoning might be.

              The SoftRock is a version of the Tayloe QSD, which is very well
              documented elsewhere, and does not (unless it is demodulating
              a pulsed signal) have a significant pulse waveform output.

              Also, you are measuring at an op-amp virtual ground, so you would
              be very lucky to see much baseband signal at all. If you really want
              to see that signal before the op-amp, you should view it on the
              source side of the input resistor, i.e. across C11 or C13, which
              conveniently provide low-impedance and RF-decoupled test points.

              [And please trim your quotes - it shouldn't be necessary to quote
              your query and all its replies - just the immediately relevant bits.]


              Regards, LenW
              --
              From Yahoo! Groups Help: ... trim all the irrelevant quoted text
              out of your message (as a courtesy to the other members of
              the group to make the digest easier to read).
            • natsystems
              Hello Len .. see below ... ... I had expected to be able to see some form of quadrature output signal from U4, but given my lack of experience, perhaps my
              Message 6 of 9 , May 2, 2007
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                Hello Len .. see below ...

                > Tell us what sort of "pulse signal" you were expecting and we may
                > be able to tell you whether you should (or more likely, should not)
                > be seeing it.

                I had expected to be able to see some form of quadrature output
                signal from U4, but given my lack of experience, perhaps my question
                should have been: "what should I expect to see on the OP Amp input
                pins?"

                > The SoftRock is a version of the Tayloe QSD, which is very well
                > documented elsewhere, and does not (unless it is demodulating
                > a pulsed signal) have a significant pulse waveform output.

                I'll look to see what I can find on the net about the Tayloe QSD and
                hopefully in future be able to sound more clued-up when required.

                > [And please trim your quotes -

                And I do apologise to all for not sticking to etiquette with my
                replies.

                In any case Len, your advice on an approach for actually locating the
                problem would be greatly appreciated. 'At this time' I am much more
                intersted in just getting the unit to work, rather than having to
                understand in detail how it works.

                Cheers .. Tom.
              • w7qjq
                ... on me! ... quite ... one ... been ... errors (snip...) Tom, since you are receiving faint transmissions , I am thinking that U4 and U5 are ok and there is
                Message 7 of 9 , May 2, 2007
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                  --- In softrock40@yahoogroups.com, "natsystems" <tom@...> wrote:
                  >
                  > Hello All ...
                  >
                  > I'm new to this group and everything SDR so I know you'll go easy
                  on me!
                  >
                  > I've built an SR40 Lite kit and it is definitely receiving but
                  quite
                  > deaf. I can say that it's deaf because I've compared it to another
                  one
                  > that a friend of mine built, and there's a bit output difference
                  > between them.
                  >
                  > Since I can hear faint transmissions, and due to the board having
                  been
                  > checked out in detail by myself and someone else for potential
                  errors

                  (snip...)


                  Tom, since you are receiving "faint transmissions", I am thinking
                  that U4 and U5 are ok and there is a problem with T1. I am an
                  experienced builder and I had some difficulty "decoding" the
                  instructions for the winding and insertion arrangement. I thought
                  about it awhile and finally soldered it in. Fortunately, it worked
                  straight-away (MDS about -120 dBm) but I could just as easily have
                  chosen the wrong arrangement. (Old age may have caused much of my
                  confusion...)

                  my $.02 73

                  Sid W7QJQ
                  Oklahoma
                • natsystems
                  ... Hi Sid ... I appreciate your $.02 worth :) I too was suspicious of T1 and I went as far as re-winding a new one and very carefully following the
                  Message 8 of 9 , May 2, 2007
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                    > Tom, since you are receiving "faint transmissions", I am thinking
                    > that U4 and U5 are ok and there is a problem with T1. I am an
                    > experienced builder and I had some difficulty "decoding" the
                    > instructions for the winding and insertion arrangement. I thought
                    > about it awhile and finally soldered it in. Fortunately, it worked
                    > straight-away (MDS about -120 dBm) but I could just as easily have
                    > chosen the wrong arrangement. (Old age may have caused much of my
                    > confusion...)
                    >
                    > my $.02 73
                    >
                    > Sid W7QJQ
                    > Oklahoma
                    >
                    Hi Sid ... I appreciate your $.02 worth :)

                    I too was suspicious of T1 and I went as far as re-winding a new one
                    and very carefully following the instructions - and may I add, under
                    guidance from a friend who also checked it out! I have to say
                    that "as far as I can be sure," I think that T1 is okay now. The
                    other thing I'm dealing with here is that I've now lost any ability
                    to receive even faint transmissions, so it would appear that the
                    fault has crept in gradually. Despite what's been said previously, I
                    can see a signal on the input pins of the OP Amp (2&6) on a good
                    working unit, but I can't see any hint of a signal on the faulty
                    unit. I'm forced now to think that I need to take the plunge and
                    replace either U4 or U5.

                    As I said Sid, thanks for the donation!

                    73's ... Tom GM4DOZ
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