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Re: SoftRock40 Lite ... a bit deaf

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  • 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 1 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 2 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 3 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 4 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 5 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 6 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 7 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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