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Re: how about a SoftRock with build in audio processor?

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  • Bob Zinn
    ... That board was the inspiration but not necessarily the way to go. You are right, so, a 24 bit ADC would be a better way to go. ... That is what I was
    Message 1 of 41 , Jan 1, 2008
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      --- In softrock40@yahoogroups.com, k5nwa <k5nwa@...> wrote:
      >
      > At 06:10 AM 1/1/2008, you wrote:
      >
      > >I built the SoftRock RXTX 80/40 over the holidays and have been
      > >playing with it using an old laptop for the processing.
      > >
      > >I started looking for a better audio processor and ran across this
      >
      ><http://www.pavouk.org/hw/usbdac/en_index.html>http://www.pavouk.org/hw/usbdac/en_index.html
      > >
      > >He used a USB DAC module for a specific purpose but looking at the
      > >board, it occurred to me that it would be easy to modify it (like
      > >un-ground the inputs) to build my own USB DAC to use with the SoftRock.
      > >
      > >Then it dawned on me that it would be even better to go one step
      > >further and build the DAC _into_ the SoftRock and get RID of the audio
      > >cables and module entirely.
      > >
      > >Yes, it would require a bit of redesign of the board and soldering a
      > >few more SMDs, but they were really much easier to solder than I
      > >expected. :)
      > >
      > >It would raise price a bit, but bandwidth can be optimized and noise
      > >level reduced. Seems like a win, all the way around. With a bit more
      > >thought, full control of the SoftRock can probably be accomplished via
      > >the same USB line.
      > >
      > >Am I missing a 'downside'?
      > >
      > >73 de N5bz
      > >
      >
      > It's doable with a couple of extra components, but be aware that it's
      > a 16 bit ADC that you have there

      That board was the 'inspiration' but not necessarily the way to go.

      You are right, so, a 24 bit ADC would be a better way to go.

      > , it will work but you will lose
      > dynamic range. The "DAC is the output side of the equation, that
      > would be used to drive a pair of headphones or the transmitter side
      > of a RxTx, the ADC is the source of data to the PC whose pins are now
      > grounded, they would connect to the SoftRock outputs.

      That is what I was thinking.

      > If you have the ADC powered by the same power as the SoftRock and
      > physically close with short heavy wires, you will minimize the center
      > hump

      The center hump seems to be from the Local oscillator [at least I can
      hear it strongly radiated in a nearby receiver], some good shielding
      may also be needed. Of course, I don't have the softrock in a case, yet.

      > , it may not go completely away because the ADC chip has an input
      > offset, but it may be just a narrow spike instead of that broad
      > noise, but even that could eliminated with some circuitry on the
      > inputs to compensate for the offsets.
      >
      > He provides Eagle drawings, you can get a free limited version of
      > eagle to fix the board up, so it looks like this would an interesting
      > project, a "USB SoftRock".
      >
      > If you build it let us know how it works out, it will be inexpensive
      > and handy for a laptop.

      A USB DAC ADC daughter board for the earlier SoftRocks would also be
      possible, Allowing a retrofit of earlier versions.

      >
      >
      >
      > Cecil
      > K5NWA
      > www.softrockradio.org www.qrpradio.com
      >
      > "Blessed are the cracked, for they shall let in the light."

      It is a beautiful day to be alive, isn't it? [every day]

      >
    • unmanagedtn
      On pin 1 (top left of U8) I have 4.9 volts! :( and on pen seven I have 2.48 volts :) I am testing things out now and had to pull this thread and info out of
      Message 41 of 41 , Jan 21, 2008
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        On pin 1 (top left of U8) I have 4.9 volts! :(
        and on pen seven I have 2.48 volts :)

        I am testing things out now and had to pull this thread and info out
        of another topic....

        Tony does this mean that U8 needs to be replaced?

        I see the same things on both sides.

        73
        ke4tvv


        > No RX image rejection results when one of the I / Q signals from the
        RXTX board is not getting to the stereo soundcard line-in input. The
        problem could be on the RXTX board, in the cable or at the soundcard.
        Also, if I and Q signal lines are shorted together no image rejection
        will be the result.
        >
        > There have been a few cases of U8 failing when the RXTX board I / Q
        output signals were connected to a soundcard when an AC voltage
        difference existed between the soundcard ground and the ground on the
        RXTX board. Please check the DC voltages at pins 1 and 7 of U8 to see
        if the two pins are still at about 2.5 volts with reference to circuit >
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