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How should I set the input level to my sound card for best RX(TX) performance?

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  • warrenallgyer
    ...... and why should I bother? Answer: for the most part you need not bother. The software that I use; HDSDR, Rocky, WSPR are all very tolerant of input
    Message 1 of 22 , Jan 23, 2013
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      ...... and why should I bother?

      Answer: for the most part you need not bother. The software that I use; HDSDR, Rocky, WSPR are all very tolerant of input levels. This procedure is not going to help you hear weaker signals.

      You should care however if you want to assure maximum sensitivity AND maximum protection against overload from strong signals at the same time. Overload produces spurious signals, interference, and 'trash' on the band display.

      In my location I have very strong HF broadcast stations that easily overload a receiver on 80, 40, and 30 meters. I have used external attenuators to help manage this but they are a problem if you also want to transmit. I have modified one of my RXTX with an internal attenuator which works great but, it turns out, is a much more complex answer to the problem than is necessary.

      The trick is to set the PC input level to the minimum possible for weak signal reception. This will then allow the largest possible signal to be received before overloading the sound card.

      So how low can you go?

      On HF the ability to receive weak signals is limited by atmospheric noise. In general you cannot receive signals below the noise (yes I am a WSPR user.... I know.... I know... but that is a separate discussion). So, as Alan often points out, if the noise level rises when you connect your antenna, then your receiver is as sensitive as is necessary to receive the weakest signal available. The noise only needs to rise a few dB, less than one S unit.

      However, depending on the antenna, the gain settings of the PC, and local noise conditions I often see the noise floor rise 20-30 dB when the antenna is connected. This does nothing to make the weak signals more useable. It does, however make all signals higher in level to your PC, including the very strong signals that will cause overload. This means your input level is set too high.

      So.... to set the input sound level you should connect the antenna (tuned to the band you are using if you use a tuner) and reduce the level using the Sound control panel until you just see a noticeable increase when the antenna is connected. Doing this will give the maximum dynamic range for your receiver/PC combo and maximize it's ability to handle big signals without losing any sensitivity.

      I find HDSDR the best tool for viewing noise levels. You can use the sliders to adjust the vertical scale and position and you can average up to 128 samples with the drop down. This gives a relatively smooth average of the noise both with and without the antenna. Don't use Rocky for this... I am not sure how Alex does it but his noise floor never moves.

      Final step: recalibrate your S meter because it will likely read much lower than it did before. If you don't have a calibration signal of a known level then take a reading of a stable signal before doing the adjustment and reset to that same level after you are done.

      For the most part you will see absolutely no change in receiver performance unless you were experiencing overload before. Overload in my RXTX shows as strong carriers with no modulation every 10 KHz of so. But overload can also introduce spurious signals or "ghosts" that are not real. You band will be as clean as it possibly can be.

      With my 40 meter RXTX I can 'hear' signals just a few dB out of the noise, normally around -110 dB, and also receiver the broadcast signals as high as -15 dB (about 60 dB over S9) without noticeable overload. That's 95 dB of useable dynamic range and that is pretty good by anyone's standards.

      Warren Allgyer - W8TOD
    • Alan
      ... Subject: [softrock40] How should I set the input level to my sound card for best RX(TX) performance? ... Warren, This means your RF antenna input is too
      Message 2 of 22 , Jan 23, 2013
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        ----- Original Message -----
        Subject: [softrock40] How should I set the input level to my sound card for best RX(TX) performance?


        > However, depending on the antenna, the gain settings of the PC, and local noise conditions I often see the noise floor rise 20-30
        > dB when the antenna is connected. This does nothing to make the weak signals more useable. It does, however make all signals
        > higher in level to your PC, including the very strong signals that will cause overload. This means your input level is set too
        > high.

        Warren,

        This means your RF antenna input is too high.

        Regardless of where the soundcard gain is set an RF attenuator is needed so only a slight increase in noise is seen when connecting
        the antenna.
        Then the soundcard gain should be set so you can just see the weakest signals.

        How does that sound?

        73 Alan G4ZFQ


        >
        > So.... to set the input sound level you should connect the antenna (tuned to the band you are using if you use a tuner) and reduce
        > the level using the Sound control panel until you just see a noticeable increase when the antenna is connected. Doing this will
        > give the maximum dynamic range for your receiver/PC combo and maximize it's ability to handle big signals without losing any
        > sensitivity.
        >
        > I find HDSDR the best tool for viewing noise levels. You can use the sliders to adjust the vertical scale and position and you can
        > average up to 128 samples with the drop down. This gives a relatively smooth average of the noise both with and without the
        > antenna. Don't use Rocky for this... I am not sure how Alex does it but his noise floor never moves.
        >
        > Final step: recalibrate your S meter because it will likely read much lower than it did before. If you don't have a calibration
        > signal of a known level then take a reading of a stable signal before doing the adjustment and reset to that same level after you
        > are done.
        >
        > For the most part you will see absolutely no change in receiver performance unless you were experiencing overload before. Overload
        > in my RXTX shows as strong carriers with no modulation every 10 KHz of so. But overload can also introduce spurious signals or
        > "ghosts" that are not real. You band will be as clean as it possibly can be.
        >
        > With my 40 meter RXTX I can 'hear' signals just a few dB out of the noise, normally around -110 dB, and also receiver the
        > broadcast signals as high as -15 dB (about 60 dB over S9) without noticeable overload. That's 95 dB of useable dynamic range and
        > that is pretty good by anyone's standards.
        >
      • Roger Critchlow
        Warren -- All this is doing is attenuating the sound card input after it s been converted to bits, which will reduce the levels of the signals going through
        Message 3 of 22 , Jan 23, 2013
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          Warren --

          All this is doing is attenuating the sound card input after it's been converted to bits, which will reduce the levels of the signals going through the SDR software, but not fix any overloading problems that occurred earlier. 

          You've got 16 bits of dynamic range in measuring voltages coming out of the op amps after the mixer.  If the voltages are overflowing that range, then the signals are being clipped at conversion and nothing you subsequently do will recover the part that got clipped off.  To prevent the clipping, you can reduce the RF level with attenuation before the mixer, or you can reduce the amplification after the mixer and increase the number of bits.

          Going back to an earlier discussion which I accidentally deleted, getting 24 or even 32 bits of analog-to-digital-conversion is only difficult and expensive if you insist on high sample rates at the same time.  If you focus on receiving and transmitting amateur communication channels, then a converter that runs at 8kHz is enough.  If you focus on drawing spectrum and waterfall displays, then a converter that produces 8 bit samples is enough.  But if you want 24 bit resolution at 192kHz, ah, now we're talking some serious gear and non-trivial engineering and clock rates that will warm a freezing shack.

          -- rec --


          On Wed, Jan 23, 2013 at 10:02 AM, Alan <alan4alan@...> wrote:
           


          ----- Original Message -----
          Subject: [softrock40] How should I set the input level to my sound card for best RX(TX) performance?

          > However, depending on the antenna, the gain settings of the PC, and local noise conditions I often see the noise floor rise 20-30
          > dB when the antenna is connected. This does nothing to make the weak signals more useable. It does, however make all signals
          > higher in level to your PC, including the very strong signals that will cause overload. This means your input level is set too
          > high.

          Warren,

          This means your RF antenna input is too high.

          Regardless of where the soundcard gain is set an RF attenuator is needed so only a slight increase in noise is seen when connecting
          the antenna.
          Then the soundcard gain should be set so you can just see the weakest signals.

          How does that sound?

          73 Alan G4ZFQ


          >
          > So.... to set the input sound level you should connect the antenna (tuned to the band you are using if you use a tuner) and reduce
          > the level using the Sound control panel until you just see a noticeable increase when the antenna is connected. Doing this will
          > give the maximum dynamic range for your receiver/PC combo and maximize it's ability to handle big signals without losing any
          > sensitivity.
          >
          > I find HDSDR the best tool for viewing noise levels. You can use the sliders to adjust the vertical scale and position and you can
          > average up to 128 samples with the drop down. This gives a relatively smooth average of the noise both with and without the
          > antenna. Don't use Rocky for this... I am not sure how Alex does it but his noise floor never moves.
          >
          > Final step: recalibrate your S meter because it will likely read much lower than it did before. If you don't have a calibration
          > signal of a known level then take a reading of a stable signal before doing the adjustment and reset to that same level after you
          > are done.
          >
          > For the most part you will see absolutely no change in receiver performance unless you were experiencing overload before. Overload
          > in my RXTX shows as strong carriers with no modulation every 10 KHz of so. But overload can also introduce spurious signals or
          > "ghosts" that are not real. You band will be as clean as it possibly can be.
          >
          > With my 40 meter RXTX I can 'hear' signals just a few dB out of the noise, normally around -110 dB, and also receiver the
          > broadcast signals as high as -15 dB (about 60 dB over S9) without noticeable overload. That's 95 dB of useable dynamic range and
          > that is pretty good by anyone's standards.
          >


        • warrenallgyer
          Roger I am going to disagree with you a bit here. I believe you will find that the Sound Input, or Record level control on a PC actually controls the level of
          Message 4 of 22 , Jan 23, 2013
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            Roger

            I am going to disagree with you a bit here.

            I believe you will find that the Sound Input, or Record level control on a PC actually controls the level of the analog signal before it is converted to bits. It is used to do exactly what I am recommending: to place the portion of the analog signal that contains the audio you want into the range of the analog to digital converter.

            You can test this yourself if you do what I did:

            Before I changed anything my overload symptoms began showing up with signal generator input levels at about -35 dBm. I put an attenuator in the receiver input (actually just a 10:1 voltage divider) between L4 and C39 which gave me 20 dB of attenuation. After this I was able, as you would expect, to run the signal generator up to -15 dBm before the overload began.

            So I took the voltage divider out and reduced the sound card input level control by 20 dB (watching the S meter with a calibration signal in). Same result: I was able to run up to -15 dBm before the overload started.

            So then I did the procedure described in the post and got about 5 dB more before the overload started. Once I re-calibrated the S Meter the noise floor came back to where it was before…about -110 dB and the system easily accommodated -10 dBm or so without overload.

            The overload that I am experiencing is not "occurring earlier".... it is clearly happening in the input stage of the PC card.

            Always willing to listen to alternative points of view.........

            Warren Allgyer - W8TOD

            --- In softrock40@yahoogroups.com, Roger Critchlow wrote:
            >
            > Warren --
            >
            > All this is doing is attenuating the sound card input after it's been
            > converted to bits, which will reduce the levels of the signals going
            > through the SDR software, but not fix any overloading problems that
            > occurred earlier.
          • Alan
            ... Subject: [softrock40] Re: How should I set the input level to my sound card for best RX(TX) performance? ... Warren, In order to get the best dynamic range
            Message 5 of 22 , Jan 23, 2013
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              ----- Original Message -----
              Subject: [softrock40] Re: How should I set the input level to my sound card for best RX(TX) performance?


              >I believe you will find that the Sound Input, or Record level control on a PC actually controls the level of the analog signal
              >before it is converted to bits. It is used to do exactly what I am recommending: to place the portion of the analog signal that
              >contains the audio you want into the range of the analog to digital converter.

              Warren,

              In order to get the best dynamic range the principle is the same with all parts of the receive system.
              The front end Softrock should be fed with a signal which will just overcome the Softrock's noise level. Use an attenuator if
              necessary.
              Then the soundcard ADC should be fed with a signal that just overcomes the soundcard noise level. The lowest possible setting should
              be used.

              No numerical tests are needed to set this, just observations of the noise level.

              73 Alan G4XFQ




              You can test this yourself if you do what I did:

              Before I changed anything my overload symptoms began showing up with signal generator input levels at about -35 dBm. I put an
              attenuator in the receiver input (actually just a 10:1 voltage divider) between L4 and C39 which gave me 20 dB of attenuation. After
              this I was able, as you would expect, to run the signal generator up to -15 dBm before the overload began.

              So I took the voltage divider out and reduced the sound card input level control by 20 dB (watching the S meter with a calibration
              signal in). Same result: I was able to run up to -15 dBm before the overload started.

              So then I did the procedure described in the post and got about 5 dB more before the overload started. Once I re-calibrated the S
              Meter the noise floor came back to where it was before.about -110 dB and the system easily accommodated -10 dBm or so without
              overload.

              The overload that I am experiencing is not "occurring earlier".... it is clearly happening in the input stage of the PC card.

              Always willing to listen to alternative points of view.........

              Warren Allgyer - W8TOD

              --- In softrock40@yahoogroups.com, Roger Critchlow wrote:
              >
              > Warren --
              >
              > All this is doing is attenuating the sound card input after it's been
              > converted to bits, which will reduce the levels of the signals going
              > through the SDR software, but not fix any overloading problems that
              > occurred earlier.
            • warrenallgyer
              Completely agree this will work Alan. But reducing the iput level of the sound card as I suggest will accomplish both results in one step. The reason is the RX
              Message 6 of 22 , Jan 23, 2013
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                Completely agree this will work Alan.

                But reducing the iput level of the sound card as I suggest will accomplish both results in one step.

                The reason is the RX is a very linear device. Since this conversation started I have proven that to myself.

                I put my MFJ analyzer through a 0-21 dB step attenuator and measured it on the spectrum analyzer and its' output on 7040 is nominally 0 dBM. I put this signal directly into the antenna input and put a scope on the IQ cross-over that is the output of the op amps. The signal there was a 5 V P-P square wave. I began progressively switching in attenuation to the input signal until the op am output just returned to a sine wave at 4.85 V P-P.... they were no longer being driven to the supply rail. The signal input at this point was about -11 dBM.

                This is the only part of the RX chain that can produce non linearity or overload.

                So I am of the belief the RXTX can deliver up to a minus 11-13 dBm signal to the PC without overloading. My PC card cannot accept anything higher than that.

                So by reducing the gain of the PC card it can handle all my RXTX can produce without overload.

                If you attenuate the input to reduce the signal and noise and then correspondingly increase the gain of the op amps you will improve the dynamic range of the radio but you still have to squeeze it through the input card which cannot handle more than 95 dB of dynamic range.

                .......leading to ... I know..... buy a better input card.

                So I had 70 dB of dynamic range when I started and now I have 95. If I change the gain of the op amps, put attenuators in the front end, and buy a 24 bit card what will I have? 110?

                I think I am going to take my free 25 dB and call it done for now.

                Warren Allgyer - W8TOD


                > Warren,
                >
                > In order to get the best dynamic range the principle is the same with all parts of the receive system.
                > The front end Softrock should be fed with a signal which will just overcome the Softrock's noise level. Use an attenuator if
                > necessary.
                > Then the soundcard ADC should be fed with a signal that just overcomes the soundcard noise level. The lowest possible setting should
                > be used.
                >
                > No numerical tests are needed to set this, just observations of the noise level.
                >
                > 73 Alan G4XFQ
              • warrenallgyer
                BTW the rig in question has been on WSPR off and on since 12:00 UTC. The database would indicate its performance seems uncompromised by my controversial
                Message 7 of 22 , Jan 23, 2013
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                  BTW the rig in question has been on WSPR off and on since 12:00 UTC. The database would indicate its' performance seems uncompromised by my controversial approach.
                • Alan
                  ... Subject: [softrock40] Re: How should I set the input level to my sound card for best RX(TX) performance? ... Warren, Sorry, I jumped in without reading the
                  Message 8 of 22 , Jan 23, 2013
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                    ----- Original Message -----
                    Subject: [softrock40] Re: How should I set the input level to my sound card for best RX(TX) performance?


                    > Completely agree this will work Alan.
                    >

                    Warren,

                    Sorry, I jumped in without reading the subject line.
                    Yes, keeping the audio as low as possible is all that can be done with the RXTX.


                    Tony uses attenuators in the lower ranges of the RX Ensemble. I think it would be an idea to do this with the LF RXTXs.
                    While your soundcard may not overload before the Softrock opamps this may not always be the case. Where in a soundcard is the input
                    attenuator? I think I've seen active input devices coming before any attenuator.
                    And really good antennas will possibly reduce the margin.

                    73 Alan G4ZFQ
                  • warrenallgyer
                    Alan No problem at all.... I have never posted quickly without fully understanding the post I was replying to........ HAH! I spent a couple of hours this
                    Message 9 of 22 , Jan 24, 2013
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                      Alan

                      No problem at all.... I have never posted quickly without fully understanding the post I was replying to........ HAH!

                      I spent a couple of hours this afternoon trying to figure out at what level the basic RXTX goes into overload. It seems that the rig is extraordinarily linear right up to the point that the output begins clipping in the op amps. That happens right at 5 V P-P on the audio out. Up until that point the radio seems very linear from Minimum Detectable Signal all the way up to clip. So I set the generator to 10 MHz out and tuned HDSDR to 10.010 MHz in order to generate a 10 KHz IQ signal out for the scope.

                      I put my signal generator, which outputs nominally +10 dBm, into a series of pads and started down the scale to find the point at which the op amps stopped clipping. At +10 dBm the op amps were making very nice 10 KHz square waves! 21 dB later, at -11 dBm, the clipping magically stopped and the output measured 4.96 V P-P. immediately at this level, and all the way down to -110 or so, when I reduced the RF input by one dB the audio output dropped a corresponding 1 dB.... indicating linearity for nearly 100 dB.

                      My sound card is a little tighter. If I hit it with 4.96 volts of audio, even with the gain minimized, it still generates spurious signals. Reducing the input RF to -15 dBm reduced the audio out a corresponding 4 dB to 3.0 volts and the spurious signals disappeared.

                      I did confirm, by setting the sound card gain back to its' previous normal position at about 80%, that the spurs then began with an RF input level of -35 dBm.

                      Bottom line is my Realtek audio card is currently the limiting factor in my total dynamic range.... by about 5 dB. I am satisfied and going any farther than this would be gilding the lily in my book.

                      ....... on the other hand.... I DO have a 24 bit USB Soundblaster X-Fi on the shelf......just maybe I will check to see if I can get that other 5 dB back.

                      Warren Allgyer - W8TOD

                      --- In softrock40@yahoogroups.com, "Alan" wrote:
                      >
                      >
                      > ----- Original Message -----
                      > Subject: [softrock40] Re: How should I set the input level to my sound card for best RX(TX) performance?
                      >
                      >
                      > > Completely agree this will work Alan.
                      > >
                      >
                      > Warren,
                      >
                      > Sorry, I jumped in without reading the subject line.
                      > Yes, keeping the audio as low as possible is all that can be done with the RXTX.
                      >
                      >
                      > Tony uses attenuators in the lower ranges of the RX Ensemble. I think it would be an idea to do this with the LF RXTXs.
                      > While your soundcard may not overload before the Softrock opamps this may not always be the case. Where in a soundcard is the input
                      > attenuator? I think I've seen active input devices coming before any attenuator.
                      > And really good antennas will possibly reduce the margin.
                      >
                      > 73 Alan G4ZFQ
                      >
                    • David Turnbull
                      ... Warren, I m pretty sure this isn t doing what you want. You want to set your sound card line-in at 0dB for the best possible dynamic range on a SoftRock or
                      Message 10 of 22 , Jan 24, 2013
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                        On Wed, Jan 23, 2013 at 7:52 AM, warrenallgyer <allgyer@...> wrote:
                        > How should I set the input level to my sound card for best RX(TX) performance?...... and why should I bother?
                        >
                        > The trick is to set the PC input level to the minimum possible for weak signal reception. This will then allow the largest possible signal to be received before overloading the sound card.

                        Warren, I'm pretty sure this isn't doing what you want.

                        You want to set your sound card line-in at 0dB for the best possible
                        dynamic range on a SoftRock or any sound card SDR. For most sound
                        cards, this means full volume. Volume settings on modern cards don't
                        adjust analog gain; it's all digital. Unfortunately, some cards also
                        provide digital gain and I'm not sure how to identify this on Windows
                        (Mac shows volume in dB). If you have a Peaberry you will find that I
                        locked the radio volume settings so it is always 0dB and the operating
                        system can't change it.

                        The only way to really add dynamic range is to adjust the LT6231 gain.
                        This is R59, R56, C45, C44 on a RXTX. Reduce these resistor values
                        until you no longer see antenna noise and/or weak signals. The OpAmp
                        is an integrator and the formula is f=1/(2*pi*c*r). Given the resistor
                        r(in ohms) find a value for c(in F) where f(in Hz) is greater than the
                        bandwidth of your sound card. By default, these radios are set for
                        96k. If your sound card has an anti-aliasing filter then you can
                        simply remove the capacitors and leave them off.

                        You might find an additional 20dB by using this procedure. It depends
                        on the quality of your sound card and cables. Unfortunately, you will
                        also find that WSPR no longer decodes in I/Q mode and will have to run
                        HDSDR or PowerSDR and connect to WSPR with VAC.

                        73 David AE9RB
                        http://AE9RB.com/
                      • warrenallgyer
                        David You and Roger make the same point and I cannot argue whether the sound card control works in the analog domain prior to ADC or in the digital domain post
                        Message 11 of 22 , Jan 24, 2013
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                          David

                          You and Roger make the same point and I cannot argue whether the sound card control works in the analog domain prior to ADC or in the digital domain post ADC. Perhaps some do one and some do the other. I have not looked at the circuitry, only the behavior.

                          However I am very sure that my sound card overloaded at -35 dBM RF input with the gain at 80 % and at -15 dBM with the gain minimized. And, in both cases, a -110 dBm signal gave me the same rise above the noise floor.

                          I can't see how that can happen if the gain control works post ADC.

                          Put another way..... my receiver exhibits 80 dB of dynamic range between noise floor and overload with the input gain set at 80%. It exhibits 100 dB of dynamic range with the gain set at minimum. In both cases the weak signal performance is the same.

                          The WSPR decodes I got on 40 meters last night were all with the input gain at this minimal setting and it was easily the best night in recent weeks for me.

                          Where am I going wrong?

                          Warren Allgyer - W8TOD

                          --- In softrock40@yahoogroups.com, David Turnbull wrote:
                          >
                          > On Wed, Jan 23, 2013 at 7:52 AM, warrenallgyer wrote:
                          > > How should I set the input level to my sound card for best RX(TX) performance?...... and why should I bother?
                          > >
                          > > The trick is to set the PC input level to the minimum possible for weak signal reception. This will then allow the largest possible signal to be received before overloading the sound card.
                          >
                          > Warren, I'm pretty sure this isn't doing what you want.
                          >
                          > You want to set your sound card line-in at 0dB for the best possible
                          > dynamic range on a SoftRock or any sound card SDR. For most sound
                          > cards, this means full volume. Volume settings on modern cards don't
                          > adjust analog gain; it's all digital. Unfortunately, some cards also
                          > provide digital gain and I'm not sure how to identify this on Windows
                          > (Mac shows volume in dB). If you have a Peaberry you will find that I
                          > locked the radio volume settings so it is always 0dB and the operating
                          > system can't change it.
                          >
                          > The only way to really add dynamic range is to adjust the LT6231 gain.
                          > This is R59, R56, C45, C44 on a RXTX. Reduce these resistor values
                          > until you no longer see antenna noise and/or weak signals. The OpAmp
                          > is an integrator and the formula is f=1/(2*pi*c*r). Given the resistor
                          > r(in ohms) find a value for c(in F) where f(in Hz) is greater than the
                          > bandwidth of your sound card. By default, these radios are set for
                          > 96k. If your sound card has an anti-aliasing filter then you can
                          > simply remove the capacitors and leave them off.
                          >
                          > You might find an additional 20dB by using this procedure. It depends
                          > on the quality of your sound card and cables. Unfortunately, you will
                          > also find that WSPR no longer decodes in I/Q mode and will have to run
                          > HDSDR or PowerSDR and connect to WSPR with VAC.
                          >
                          > 73 David AE9RB
                          > http://AE9RB.com/
                          >
                        • Alan
                          ... Subject: Re: [softrock40] How should I set the input level to my sound card for best RX(TX) performance? ... Dave, It is probably the best that can be done
                          Message 12 of 22 , Jan 24, 2013
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                            ----- Original Message -----
                            Subject: Re: [softrock40] How should I set the input level to my sound card for best RX(TX) performance?
                            >> The trick is to set the PC input level to the minimum possible for weak signal reception. This will then allow the largest
                            >> possible signal to be received before overloading the sound card.
                            >
                            > Warren, I'm pretty sure this isn't doing what you want.
                            >

                            Dave,

                            It is probably the best that can be done on a basic Softrock RXTX. Warren does seem to have figures to show that.
                            Of course, that is just one series of tests.

                            If we are talking mods then yes, maximum soundcard gain and minimum Softrock, or Peaberry, gain. Probably an RF attenuator for the
                            difficult situations.
                            Then advantage may be made of a low noise 24 bit card.

                            On Windows soundcard gain is sometimes shown in dB, it depends on the card and, obviously, driver.

                            I'm puzzled by your WSPR-IQ comment. Is this a fault in WSPR?

                            73 Alan G4ZFQ

                            > You want to set your sound card line-in at 0dB for the best possible
                            > dynamic range on a SoftRock or any sound card SDR. For most sound
                            > cards, this means full volume. Volume settings on modern cards don't
                            > adjust analog gain; it's all digital. Unfortunately, some cards also
                            > provide digital gain and I'm not sure how to identify this on Windows
                            > (Mac shows volume in dB). If you have a Peaberry you will find that I
                            > locked the radio volume settings so it is always 0dB and the operating
                            > system can't change it.
                            >
                            > The only way to really add dynamic range is to adjust the LT6231 gain.
                            > This is R59, R56, C45, C44 on a RXTX. Reduce these resistor values
                            > until you no longer see antenna noise and/or weak signals. The OpAmp
                            > is an integrator and the formula is f=1/(2*pi*c*r). Given the resistor
                            > r(in ohms) find a value for c(in F) where f(in Hz) is greater than the
                            > bandwidth of your sound card. By default, these radios are set for
                            > 96k. If your sound card has an anti-aliasing filter then you can
                            > simply remove the capacitors and leave them off.
                            >
                            > You might find an additional 20dB by using this procedure. It depends
                            > on the quality of your sound card and cables. Unfortunately, you will
                            > also find that WSPR no longer decodes in I/Q mode and will have to run
                            > HDSDR or PowerSDR and connect to WSPR with VAC.
                            >
                          • David Turnbull
                            I looked at my iMic and it seems that it only offers gain and no attenuation on the line in. I didn t test this; it s what the USB enumeration reports. Seems
                            Message 13 of 22 , Jan 24, 2013
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                              I looked at my iMic and it seems that it only offers gain and no
                              attenuation on the line in. I didn't test this; it's what the USB
                              enumeration reports. Seems to match your report though. Maybe I got it
                              wrong and most sound cards need it set at minimum, not maximum, or
                              maybe it's just random. I wish Windows had a better volume mixer that
                              would report dB because this information is readily available behind
                              the scenes.

                              If Rocky runs on your computer it will show the noise floor in -dBFS.
                              This is decibels below full scale. Adjust the line-in volume for the
                              lowest number (it's negative so bigger is better).

                              73 David AE9RB
                              http://AE9RB.com/

                              On Thu, Jan 24, 2013 at 12:41 AM, warrenallgyer <allgyer@...> wrote:
                              > David
                              >
                              > You and Roger make the same point and I cannot argue whether the sound card control works in the analog domain prior to ADC or in the digital domain post ADC. Perhaps some do one and some do the other. I have not looked at the circuitry, only the behavior.
                              >
                              > However I am very sure that my sound card overloaded at -35 dBM RF input with the gain at 80 % and at -15 dBM with the gain minimized. And, in both cases, a -110 dBm signal gave me the same rise above the noise floor.
                              >
                              > I can't see how that can happen if the gain control works post ADC.
                              >
                              > Put another way..... my receiver exhibits 80 dB of dynamic range between noise floor and overload with the input gain set at 80%. It exhibits 100 dB of dynamic range with the gain set at minimum. In both cases the weak signal performance is the same.
                              >
                              > The WSPR decodes I got on 40 meters last night were all with the input gain at this minimal setting and it was easily the best night in recent weeks for me.
                              >
                              > Where am I going wrong?
                              >
                              > Warren Allgyer - W8TOD
                              >
                              > --- In softrock40@yahoogroups.com, David Turnbull wrote:
                              >>
                              >> On Wed, Jan 23, 2013 at 7:52 AM, warrenallgyer wrote:
                              >> > How should I set the input level to my sound card for best RX(TX) performance?...... and why should I bother?
                              >> >
                              >> > The trick is to set the PC input level to the minimum possible for weak signal reception. This will then allow the largest possible signal to be received before overloading the sound card.
                              >>
                              >> Warren, I'm pretty sure this isn't doing what you want.
                              >>
                              >> You want to set your sound card line-in at 0dB for the best possible
                              >> dynamic range on a SoftRock or any sound card SDR. For most sound
                              >> cards, this means full volume. Volume settings on modern cards don't
                              >> adjust analog gain; it's all digital. Unfortunately, some cards also
                              >> provide digital gain and I'm not sure how to identify this on Windows
                              >> (Mac shows volume in dB). If you have a Peaberry you will find that I
                              >> locked the radio volume settings so it is always 0dB and the operating
                              >> system can't change it.
                              >>
                              >> The only way to really add dynamic range is to adjust the LT6231 gain.
                              >> This is R59, R56, C45, C44 on a RXTX. Reduce these resistor values
                              >> until you no longer see antenna noise and/or weak signals. The OpAmp
                              >> is an integrator and the formula is f=1/(2*pi*c*r). Given the resistor
                              >> r(in ohms) find a value for c(in F) where f(in Hz) is greater than the
                              >> bandwidth of your sound card. By default, these radios are set for
                              >> 96k. If your sound card has an anti-aliasing filter then you can
                              >> simply remove the capacitors and leave them off.
                              >>
                              >> You might find an additional 20dB by using this procedure. It depends
                              >> on the quality of your sound card and cables. Unfortunately, you will
                              >> also find that WSPR no longer decodes in I/Q mode and will have to run
                              >> HDSDR or PowerSDR and connect to WSPR with VAC.
                              >>
                              >> 73 David AE9RB
                              >> http://AE9RB.com/
                            • David Turnbull
                              ... WSPR doesn t seem to find signals that are more than 20dB away from it s arbitrary 0dB level. You can see them clearly in the waterfall. They just don t
                              Message 14 of 22 , Jan 24, 2013
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                                On Thu, Jan 24, 2013 at 1:01 AM, Alan <alan4alan@...> wrote:
                                > I'm puzzled by your WSPR-IQ comment. Is this a fault in WSPR?

                                WSPR doesn't seem to find signals that are more than 20dB away from
                                it's arbitrary 0dB level. You can see them clearly in the waterfall.
                                They just don't decode. If you do the OpAmp gain mods then the noise
                                meter in the lower left always stays red with more than -20dB. By
                                using HDSDR or PowerSDR, you can manually set the gain and turn off
                                AGC. This VAC method seems to always outperform the I/Q mode anyways.
                                I suppose if your line-in volume has gain instead of attenuation then
                                you could fix it there too.

                                73 David AE9RB
                                http://AE9RB.com/
                              • warrenallgyer
                                For these tests I have been using the Realtek analog card inside my MSI Netbook. I have not tested the iMic. As a comparison I just took a look at my Peaberry.
                                Message 15 of 22 , Jan 24, 2013
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                                  For these tests I have been using the Realtek analog card inside my MSI Netbook. I have not tested the iMic.

                                  As a comparison I just took a look at my Peaberry. On the negative side I see some spurs (9.980 and 10.010) start to appear with a 10 MHz input at -50 dBm. On the other hand they are about 60 dB down and do not get worse as the input level is increased until I get to -17 dBm. At -18 dBm the trace is relatively clean with those spurs 50-60 dB down. At -17 dBm in all hell breaks loose and the trace is littered with spurs every 5 KHz at -60 to -70 dBm indicated. This is just about the same place the RXTX/Realtek combo breaks as well.

                                  Warren Allgyer - W8TOD

                                  --- In softrock40@yahoogroups.com, David Turnbull wrote:
                                  >
                                  > I looked at my iMic and it seems that it only offers gain and no
                                  > attenuation on the line in. I didn't test this; it's what the USB
                                  > enumeration reports. Seems to match your report though. Maybe I got it
                                  > wrong and most sound cards need it set at minimum, not maximum, or
                                  > maybe it's just random. I wish Windows had a better volume mixer that
                                  > would report dB because this information is readily available behind
                                  > the scenes.
                                  >
                                  > If Rocky runs on your computer it will show the noise floor in -dBFS.
                                  > This is decibels below full scale. Adjust the line-in volume for the
                                  > lowest number (it's negative so bigger is better).
                                  >
                                  > 73 David AE9RB
                                  > http://AE9RB.com/
                                  >
                                  > On Thu, Jan 24, 2013 at 12:41 AM, warrenallgyer wrote:
                                  > > David
                                  > >
                                  > > You and Roger make the same point and I cannot argue whether the sound card control works in the analog domain prior to ADC or in the digital domain post ADC. Perhaps some do one and some do the other. I have not looked at the circuitry, only the behavior.
                                  > >
                                  > > However I am very sure that my sound card overloaded at -35 dBM RF input with the gain at 80 % and at -15 dBM with the gain minimized. And, in both cases, a -110 dBm signal gave me the same rise above the noise floor.
                                  > >
                                  > > I can't see how that can happen if the gain control works post ADC.
                                  > >
                                  > > Put another way..... my receiver exhibits 80 dB of dynamic range between noise floor and overload with the input gain set at 80%. It exhibits 100 dB of dynamic range with the gain set at minimum. In both cases the weak signal performance is the same.
                                  > >
                                  > > The WSPR decodes I got on 40 meters last night were all with the input gain at this minimal setting and it was easily the best night in recent weeks for me.
                                  > >
                                  > > Where am I going wrong?
                                  > >
                                  > > Warren Allgyer - W8TOD
                                  > >
                                  > > --- In softrock40@yahoogroups.com, David Turnbull wrote:
                                  > >>
                                  > >> On Wed, Jan 23, 2013 at 7:52 AM, warrenallgyer wrote:
                                  > >> > How should I set the input level to my sound card for best RX(TX) performance?...... and why should I bother?
                                  > >> >
                                  > >> > The trick is to set the PC input level to the minimum possible for weak signal reception. This will then allow the largest possible signal to be received before overloading the sound card.
                                  > >>
                                  > >> Warren, I'm pretty sure this isn't doing what you want.
                                  > >>
                                  > >> You want to set your sound card line-in at 0dB for the best possible
                                  > >> dynamic range on a SoftRock or any sound card SDR. For most sound
                                  > >> cards, this means full volume. Volume settings on modern cards don't
                                  > >> adjust analog gain; it's all digital. Unfortunately, some cards also
                                  > >> provide digital gain and I'm not sure how to identify this on Windows
                                  > >> (Mac shows volume in dB). If you have a Peaberry you will find that I
                                  > >> locked the radio volume settings so it is always 0dB and the operating
                                  > >> system can't change it.
                                  > >>
                                  > >> The only way to really add dynamic range is to adjust the LT6231 gain.
                                  > >> This is R59, R56, C45, C44 on a RXTX. Reduce these resistor values
                                  > >> until you no longer see antenna noise and/or weak signals. The OpAmp
                                  > >> is an integrator and the formula is f=1/(2*pi*c*r). Given the resistor
                                  > >> r(in ohms) find a value for c(in F) where f(in Hz) is greater than the
                                  > >> bandwidth of your sound card. By default, these radios are set for
                                  > >> 96k. If your sound card has an anti-aliasing filter then you can
                                  > >> simply remove the capacitors and leave them off.
                                  > >>
                                  > >> You might find an additional 20dB by using this procedure. It depends
                                  > >> on the quality of your sound card and cables. Unfortunately, you will
                                  > >> also find that WSPR no longer decodes in I/Q mode and will have to run
                                  > >> HDSDR or PowerSDR and connect to WSPR with VAC.
                                  > >>
                                  > >> 73 David AE9RB
                                  > >> http://AE9RB.com/
                                  >
                                • warrenallgyer
                                  .... and one more point in favor of the Peaberry: With the new firmware I am seeing a device noise floor in the range of -143 to -146 dBm after S9 calibration
                                  Message 16 of 22 , Jan 24, 2013
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                                    .... and one more point in favor of the Peaberry:

                                    With the new firmware I am seeing a device noise floor in the range of -143 to -146 dBm after S9 calibration at -73. That is unnecessarily low given antenna noise levels of -120 dBm or worse. There is at least 20 dB of dynamic range going unused at the low end.

                                    Warren Allgyer - W8TOD

                                    --- In softrock40@yahoogroups.com, "warrenallgyer" wrote:
                                    >
                                    > For these tests I have been using the Realtek analog card inside my MSI Netbook. I have not tested the iMic.
                                    >
                                    > As a comparison I just took a look at my Peaberry. On the negative side I see some spurs (9.980 and 10.010) start to appear with a 10 MHz input at -50 dBm. On the other hand they are about 60 dB down and do not get worse as the input level is increased until I get to -17 dBm. At -18 dBm the trace is relatively clean with those spurs 50-60 dB down. At -17 dBm in all hell breaks loose and the trace is littered with spurs every 5 KHz at -60 to -70 dBm indicated. This is just about the same place the RXTX/Realtek combo breaks as well.
                                    >
                                    > Warren Allgyer - W8TOD
                                    >
                                    > --- In softrock40@yahoogroups.com, David Turnbull wrote:
                                    > >
                                    > > I looked at my iMic and it seems that it only offers gain and no
                                    > > attenuation on the line in. I didn't test this; it's what the USB
                                    > > enumeration reports. Seems to match your report though. Maybe I got it
                                    > > wrong and most sound cards need it set at minimum, not maximum, or
                                    > > maybe it's just random. I wish Windows had a better volume mixer that
                                    > > would report dB because this information is readily available behind
                                    > > the scenes.
                                    > >
                                    > > If Rocky runs on your computer it will show the noise floor in -dBFS.
                                    > > This is decibels below full scale. Adjust the line-in volume for the
                                    > > lowest number (it's negative so bigger is better).
                                    > >
                                    > > 73 David AE9RB
                                    > > http://AE9RB.com/
                                    > >
                                    > > On Thu, Jan 24, 2013 at 12:41 AM, warrenallgyer wrote:
                                    > > > David
                                    > > >
                                    > > > You and Roger make the same point and I cannot argue whether the sound card control works in the analog domain prior to ADC or in the digital domain post ADC. Perhaps some do one and some do the other. I have not looked at the circuitry, only the behavior.
                                    > > >
                                    > > > However I am very sure that my sound card overloaded at -35 dBM RF input with the gain at 80 % and at -15 dBM with the gain minimized. And, in both cases, a -110 dBm signal gave me the same rise above the noise floor.
                                    > > >
                                    > > > I can't see how that can happen if the gain control works post ADC.
                                    > > >
                                    > > > Put another way..... my receiver exhibits 80 dB of dynamic range between noise floor and overload with the input gain set at 80%. It exhibits 100 dB of dynamic range with the gain set at minimum. In both cases the weak signal performance is the same.
                                    > > >
                                    > > > The WSPR decodes I got on 40 meters last night were all with the input gain at this minimal setting and it was easily the best night in recent weeks for me.
                                    > > >
                                    > > > Where am I going wrong?
                                    > > >
                                    > > > Warren Allgyer - W8TOD
                                    > > >
                                    > > > --- In softrock40@yahoogroups.com, David Turnbull wrote:
                                    > > >>
                                    > > >> On Wed, Jan 23, 2013 at 7:52 AM, warrenallgyer wrote:
                                    > > >> > How should I set the input level to my sound card for best RX(TX) performance?...... and why should I bother?
                                    > > >> >
                                    > > >> > The trick is to set the PC input level to the minimum possible for weak signal reception. This will then allow the largest possible signal to be received before overloading the sound card.
                                    > > >>
                                    > > >> Warren, I'm pretty sure this isn't doing what you want.
                                    > > >>
                                    > > >> You want to set your sound card line-in at 0dB for the best possible
                                    > > >> dynamic range on a SoftRock or any sound card SDR. For most sound
                                    > > >> cards, this means full volume. Volume settings on modern cards don't
                                    > > >> adjust analog gain; it's all digital. Unfortunately, some cards also
                                    > > >> provide digital gain and I'm not sure how to identify this on Windows
                                    > > >> (Mac shows volume in dB). If you have a Peaberry you will find that I
                                    > > >> locked the radio volume settings so it is always 0dB and the operating
                                    > > >> system can't change it.
                                    > > >>
                                    > > >> The only way to really add dynamic range is to adjust the LT6231 gain.
                                    > > >> This is R59, R56, C45, C44 on a RXTX. Reduce these resistor values
                                    > > >> until you no longer see antenna noise and/or weak signals. The OpAmp
                                    > > >> is an integrator and the formula is f=1/(2*pi*c*r). Given the resistor
                                    > > >> r(in ohms) find a value for c(in F) where f(in Hz) is greater than the
                                    > > >> bandwidth of your sound card. By default, these radios are set for
                                    > > >> 96k. If your sound card has an anti-aliasing filter then you can
                                    > > >> simply remove the capacitors and leave them off.
                                    > > >>
                                    > > >> You might find an additional 20dB by using this procedure. It depends
                                    > > >> on the quality of your sound card and cables. Unfortunately, you will
                                    > > >> also find that WSPR no longer decodes in I/Q mode and will have to run
                                    > > >> HDSDR or PowerSDR and connect to WSPR with VAC.
                                    > > >>
                                    > > >> 73 David AE9RB
                                    > > >> http://AE9RB.com/
                                    > >
                                    >
                                  • Parks, Tony
                                    The complex gain of the LT6231 stage is given by (R56/R55)/(1+j6.28*f*R56*C44) where f is the frequency in Hz and j is the sqrt of -1. This results in a
                                    Message 17 of 22 , Jan 24, 2013
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                                      The complex gain of the LT6231 stage is given by (R56/R55)/(1+j6.28*f*R56*C44)  where f is the frequency in Hz and j is the sqrt of -1.  This results in a break frequency of LP filter at the LT6231 of about 1/(6.28*4.99k*220pF)=145kHz.  The simplest way to reduce the gain of the amplifier would be to increase the value of R55.  The value of R58 for the second amplifier stage in the LT6231 should also be increased in the same way R55 is increased.

                                       I have enjoyed the discussion concerning dynamic range of the RXTX RX function.  I always hope people are having fun with the kits and find them useful.

                                      73,
                                      Tony KB9YIG

                                      On Thu, Jan 24, 2013 at 5:13 AM, warrenallgyer <allgyer@...> wrote:
                                       

                                      .... and one more point in favor of the Peaberry:

                                      With the new firmware I am seeing a device noise floor in the range of -143 to -146 dBm after S9 calibration at -73. That is unnecessarily low given antenna noise levels of -120 dBm or worse. There is at least 20 dB of dynamic range going unused at the low end.

                                      Warren Allgyer - W8TOD



                                      --- In softrock40@yahoogroups.com, "warrenallgyer" wrote:
                                      >
                                      > For these tests I have been using the Realtek analog card inside my MSI Netbook. I have not tested the iMic.
                                      >
                                      > As a comparison I just took a look at my Peaberry. On the negative side I see some spurs (9.980 and 10.010) start to appear with a 10 MHz input at -50 dBm. On the other hand they are about 60 dB down and do not get worse as the input level is increased until I get to -17 dBm. At -18 dBm the trace is relatively clean with those spurs 50-60 dB down. At -17 dBm in all hell breaks loose and the trace is littered with spurs every 5 KHz at -60 to -70 dBm indicated. This is just about the same place the RXTX/Realtek combo breaks as well.
                                      >
                                      > Warren Allgyer - W8TOD
                                      >
                                      > --- In softrock40@yahoogroups.com, David Turnbull wrote:
                                      > >
                                      > > I looked at my iMic and it seems that it only offers gain and no
                                      > > attenuation on the line in. I didn't test this; it's what the USB
                                      > > enumeration reports. Seems to match your report though. Maybe I got it
                                      > > wrong and most sound cards need it set at minimum, not maximum, or
                                      > > maybe it's just random. I wish Windows had a better volume mixer that
                                      > > would report dB because this information is readily available behind
                                      > > the scenes.
                                      > >
                                      > > If Rocky runs on your computer it will show the noise floor in -dBFS.
                                      > > This is decibels below full scale. Adjust the line-in volume for the
                                      > > lowest number (it's negative so bigger is better).
                                      > >
                                      > > 73 David AE9RB
                                      > > http://AE9RB.com/
                                      > >
                                      > > On Thu, Jan 24, 2013 at 12:41 AM, warrenallgyer wrote:
                                      > > > David
                                      > > >
                                      > > > You and Roger make the same point and I cannot argue whether the sound card control works in the analog domain prior to ADC or in the digital domain post ADC. Perhaps some do one and some do the other. I have not looked at the circuitry, only the behavior.
                                      > > >
                                      > > > However I am very sure that my sound card overloaded at -35 dBM RF input with the gain at 80 % and at -15 dBM with the gain minimized. And, in both cases, a -110 dBm signal gave me the same rise above the noise floor.
                                      > > >
                                      > > > I can't see how that can happen if the gain control works post ADC.
                                      > > >
                                      > > > Put another way..... my receiver exhibits 80 dB of dynamic range between noise floor and overload with the input gain set at 80%. It exhibits 100 dB of dynamic range with the gain set at minimum. In both cases the weak signal performance is the same.
                                      > > >
                                      > > > The WSPR decodes I got on 40 meters last night were all with the input gain at this minimal setting and it was easily the best night in recent weeks for me.
                                      > > >
                                      > > > Where am I going wrong?
                                      > > >
                                      > > > Warren Allgyer - W8TOD
                                      > > >
                                      > > > --- In softrock40@yahoogroups.com, David Turnbull wrote:
                                      > > >>
                                      > > >> On Wed, Jan 23, 2013 at 7:52 AM, warrenallgyer wrote:
                                      > > >> > How should I set the input level to my sound card for best RX(TX) performance?...... and why should I bother?
                                      > > >> >
                                      > > >> > The trick is to set the PC input level to the minimum possible for weak signal reception. This will then allow the largest possible signal to be received before overloading the sound card.
                                      > > >>
                                      > > >> Warren, I'm pretty sure this isn't doing what you want.
                                      > > >>
                                      > > >> You want to set your sound card line-in at 0dB for the best possible
                                      > > >> dynamic range on a SoftRock or any sound card SDR. For most sound
                                      > > >> cards, this means full volume. Volume settings on modern cards don't
                                      > > >> adjust analog gain; it's all digital. Unfortunately, some cards also
                                      > > >> provide digital gain and I'm not sure how to identify this on Windows
                                      > > >> (Mac shows volume in dB). If you have a Peaberry you will find that I
                                      > > >> locked the radio volume settings so it is always 0dB and the operating
                                      > > >> system can't change it.
                                      > > >>
                                      > > >> The only way to really add dynamic range is to adjust the LT6231 gain.
                                      > > >> This is R59, R56, C45, C44 on a RXTX. Reduce these resistor values
                                      > > >> until you no longer see antenna noise and/or weak signals. The OpAmp
                                      > > >> is an integrator and the formula is f=1/(2*pi*c*r). Given the resistor
                                      > > >> r(in ohms) find a value for c(in F) where f(in Hz) is greater than the
                                      > > >> bandwidth of your sound card. By default, these radios are set for
                                      > > >> 96k. If your sound card has an anti-aliasing filter then you can
                                      > > >> simply remove the capacitors and leave them off.
                                      > > >>
                                      > > >> You might find an additional 20dB by using this procedure. It depends
                                      > > >> on the quality of your sound card and cables. Unfortunately, you will
                                      > > >> also find that WSPR no longer decodes in I/Q mode and will have to run
                                      > > >> HDSDR or PowerSDR and connect to WSPR with VAC.
                                      > > >>
                                      > > >> 73 David AE9RB
                                      > > >> http://AE9RB.com/
                                      > >
                                      >


                                    • warrenallgyer
                                      Awwww.... c mon Tony. You just love to watch Alan, David, Roger, and me fight.... admit it! Of course we are having fun! I have said it before: Softrocks are
                                      Message 18 of 22 , Jan 24, 2013
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                                        Awwww.... c'mon Tony. You just love to watch Alan, David, Roger, and me fight.... admit it!

                                        Of course we are having fun! I have said it before: Softrocks are more fun than Beijing KTV and, in the end, a whole lot cheaper! Look at it as a service to the planet, keeping us off the streets.

                                        Thank you always for your work Tony.

                                        Best regards,

                                        Warren Allgyer - W8TOD

                                        --- In softrock40@yahoogroups.com, "Parks, Tony" wrote:
                                        >
                                        > The complex gain of the LT6231 stage is given by
                                        > (R56/R55)/(1+j6.28*f*R56*C44) where f is the frequency in Hz and j is the
                                        > sqrt of -1. This results in a break frequency of LP filter at the LT6231
                                        > of about 1/(6.28*4.99k*220pF)=145kHz. The simplest way to reduce the gain
                                        > of the amplifier would be to increase the value of R55. The value of R58
                                        > for the second amplifier stage in the LT6231 should also be increased in
                                        > the same way R55 is increased.
                                        >
                                        > I have enjoyed the discussion concerning dynamic range of the RXTX RX
                                        > function. I always hope people are having fun with the kits and find them
                                        > useful.
                                        >
                                        > 73,
                                        > Tony KB9YIG
                                        >
                                        > On Thu, Jan 24, 2013 at 5:13 AM, warrenallgyer wrote:
                                        >
                                        > > **
                                        > >
                                        > >
                                        > > .... and one more point in favor of the Peaberry:
                                        > >
                                        > > With the new firmware I am seeing a device noise floor in the range of
                                        > > -143 to -146 dBm after S9 calibration at -73. That is unnecessarily low
                                        > > given antenna noise levels of -120 dBm or worse. There is at least 20 dB of
                                        > > dynamic range going unused at the low end.
                                        > >
                                        > > Warren Allgyer - W8TOD
                                        > >
                                        > >
                                        > > --- In softrock40@yahoogroups.com, "warrenallgyer" wrote:
                                        > > >
                                        > > > For these tests I have been using the Realtek analog card inside my MSI
                                        > > Netbook. I have not tested the iMic.
                                        > > >
                                        > > > As a comparison I just took a look at my Peaberry. On the negative side
                                        > > I see some spurs (9.980 and 10.010) start to appear with a 10 MHz input at
                                        > > -50 dBm. On the other hand they are about 60 dB down and do not get worse
                                        > > as the input level is increased until I get to -17 dBm. At -18 dBm the
                                        > > trace is relatively clean with those spurs 50-60 dB down. At -17 dBm in all
                                        > > hell breaks loose and the trace is littered with spurs every 5 KHz at -60
                                        > > to -70 dBm indicated. This is just about the same place the RXTX/Realtek
                                        > > combo breaks as well.
                                        > > >
                                        > > > Warren Allgyer - W8TOD
                                        > > >
                                        > > > --- In softrock40@yahoogroups.com, David Turnbull wrote:
                                        > > > >
                                        > > > > I looked at my iMic and it seems that it only offers gain and no
                                        > > > > attenuation on the line in. I didn't test this; it's what the USB
                                        > > > > enumeration reports. Seems to match your report though. Maybe I got it
                                        > > > > wrong and most sound cards need it set at minimum, not maximum, or
                                        > > > > maybe it's just random. I wish Windows had a better volume mixer that
                                        > > > > would report dB because this information is readily available behind
                                        > > > > the scenes.
                                        > > > >
                                        > > > > If Rocky runs on your computer it will show the noise floor in -dBFS.
                                        > > > > This is decibels below full scale. Adjust the line-in volume for the
                                        > > > > lowest number (it's negative so bigger is better).
                                        > > > >
                                        > > > > 73 David AE9RB
                                        > > > > http://AE9RB.com/
                                        > > > >
                                        > > > > On Thu, Jan 24, 2013 at 12:41 AM, warrenallgyer wrote:
                                        > > > > > David
                                        > > > > >
                                        > > > > > You and Roger make the same point and I cannot argue whether the
                                        > > sound card control works in the analog domain prior to ADC or in the
                                        > > digital domain post ADC. Perhaps some do one and some do the other. I have
                                        > > not looked at the circuitry, only the behavior.
                                        > > > > >
                                        > > > > > However I am very sure that my sound card overloaded at -35 dBM RF
                                        > > input with the gain at 80 % and at -15 dBM with the gain minimized. And, in
                                        > > both cases, a -110 dBm signal gave me the same rise above the noise floor.
                                        > > > > >
                                        > > > > > I can't see how that can happen if the gain control works post ADC.
                                        > > > > >
                                        > > > > > Put another way..... my receiver exhibits 80 dB of dynamic range
                                        > > between noise floor and overload with the input gain set at 80%. It
                                        > > exhibits 100 dB of dynamic range with the gain set at minimum. In both
                                        > > cases the weak signal performance is the same.
                                        > > > > >
                                        > > > > > The WSPR decodes I got on 40 meters last night were all with the
                                        > > input gain at this minimal setting and it was easily the best night in
                                        > > recent weeks for me.
                                        > > > > >
                                        > > > > > Where am I going wrong?
                                        > > > > >
                                        > > > > > Warren Allgyer - W8TOD
                                        > > > > >
                                        > > > > > --- In softrock40@yahoogroups.com, David Turnbull wrote:
                                        > > > > >>
                                        > > > > >> On Wed, Jan 23, 2013 at 7:52 AM, warrenallgyer wrote:
                                        > > > > >> > How should I set the input level to my sound card for best RX(TX)
                                        > > performance?...... and why should I bother?
                                        > > > > >> >
                                        > > > > >> > The trick is to set the PC input level to the minimum possible
                                        > > for weak signal reception. This will then allow the largest possible signal
                                        > > to be received before overloading the sound card.
                                        > > > > >>
                                        > > > > >> Warren, I'm pretty sure this isn't doing what you want.
                                        > > > > >>
                                        > > > > >> You want to set your sound card line-in at 0dB for the best possible
                                        > > > > >> dynamic range on a SoftRock or any sound card SDR. For most sound
                                        > > > > >> cards, this means full volume. Volume settings on modern cards don't
                                        > > > > >> adjust analog gain; it's all digital. Unfortunately, some cards also
                                        > > > > >> provide digital gain and I'm not sure how to identify this on
                                        > > Windows
                                        > > > > >> (Mac shows volume in dB). If you have a Peaberry you will find that
                                        > > I
                                        > > > > >> locked the radio volume settings so it is always 0dB and the
                                        > > operating
                                        > > > > >> system can't change it.
                                        > > > > >>
                                        > > > > >> The only way to really add dynamic range is to adjust the LT6231
                                        > > gain.
                                        > > > > >> This is R59, R56, C45, C44 on a RXTX. Reduce these resistor values
                                        > > > > >> until you no longer see antenna noise and/or weak signals. The OpAmp
                                        > > > > >> is an integrator and the formula is f=1/(2*pi*c*r). Given the
                                        > > resistor
                                        > > > > >> r(in ohms) find a value for c(in F) where f(in Hz) is greater than
                                        > > the
                                        > > > > >> bandwidth of your sound card. By default, these radios are set for
                                        > > > > >> 96k. If your sound card has an anti-aliasing filter then you can
                                        > > > > >> simply remove the capacitors and leave them off.
                                        > > > > >>
                                        > > > > >> You might find an additional 20dB by using this procedure. It
                                        > > depends
                                        > > > > >> on the quality of your sound card and cables. Unfortunately, you
                                        > > will
                                        > > > > >> also find that WSPR no longer decodes in I/Q mode and will have to
                                        > > run
                                        > > > > >> HDSDR or PowerSDR and connect to WSPR with VAC.
                                        > > > > >>
                                        > > > > >> 73 David AE9RB
                                        > > > > >> http://AE9RB.com/
                                        > > > >
                                        > > >
                                        > >
                                        > >
                                        > >
                                        >
                                      • warrenallgyer
                                        I have done some work overnight to try to correlate a WSPR noise level of 0 to an actual noise level on HDSDR. It seems pretty consistent: Using the sound
                                        Message 19 of 22 , Jan 24, 2013
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                                          I have done some work overnight to try to correlate a WSPR noise level of "0" to an actual noise level on HDSDR.

                                          It seems pretty consistent: Using the sound card input level to adjust for "0" during WSPR receive, then switching to HDSDR, the noise floor seems to be about -90 dBm. So it seems WSPR wants to see that level of noise to be comfortable.

                                          I have not figured an objective way of comparing WSPR decodes at this level versus the minimal setting I am using now as a norm. My gut tells me the minimal setting misses some decodes that I get with having a -90 noise floor but I cannot be sure.

                                          Warren Allgyer - W8TOD

                                          --- In softrock40@yahoogroups.com, David Turnbull wrote:
                                          >
                                          > On Thu, Jan 24, 2013 at 1:01 AM, Alan wrote:
                                          > > I'm puzzled by your WSPR-IQ comment. Is this a fault in WSPR?
                                          >
                                          > WSPR doesn't seem to find signals that are more than 20dB away from
                                          > it's arbitrary 0dB level. You can see them clearly in the waterfall.
                                          > They just don't decode. If you do the OpAmp gain mods then the noise
                                          > meter in the lower left always stays red with more than -20dB. By
                                          > using HDSDR or PowerSDR, you can manually set the gain and turn off
                                          > AGC. This VAC method seems to always outperform the I/Q mode anyways.
                                          > I suppose if your line-in volume has gain instead of attenuation then
                                          > you could fix it there too.
                                          >
                                          > 73 David AE9RB
                                          > http://AE9RB.com/
                                          >
                                        • warrenallgyer
                                          Further to this and, hopefully, my final note on the subject, I have run WSPR on 20 meters this afternoon for a little over an hour, alternating every few
                                          Message 20 of 22 , Jan 24, 2013
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                                            Further to this and, hopefully, my final note on the subject, I have run WSPR on 20 meters this afternoon for a little over an hour, alternating every few cycles with the sound card input level set to minimum and maximum. At minimum the WSPR noise indicator showed -30, -30 and at maximum it showed -8, -8.

                                            If you are interested in the results you can check the WSPR database for my reception reports from 02:00 to 03:12 UTC on 1/25. During this period I spotted the same stations multiple times with each setting. I can find no correlation between the sound card setting and the SNR or the number of spots. Both settings seem to work equally well.

                                            If you read the log here are the times I changed the level:

                                            02:00 Changed to maximum
                                            02:12 Changed to minimum
                                            02:40 Changed to maximum
                                            02:56 Changed to minimum
                                            03:18 Changed to maximum

                                            "Minimum" in this case is one increment above the bottom. At the bottom step the control seems to mute the audio.

                                            Warren Allgyer - W8TOD

                                            --- In softrock40@yahoogroups.com, "warrenallgyer" wrote:
                                            >
                                            > I have done some work overnight to try to correlate a WSPR noise level of "0" to an actual noise level on HDSDR.
                                            >
                                            > It seems pretty consistent: Using the sound card input level to adjust for "0" during WSPR receive, then switching to HDSDR, the noise floor seems to be about -90 dBm. So it seems WSPR wants to see that level of noise to be comfortable.
                                            >
                                            > I have not figured an objective way of comparing WSPR decodes at this level versus the minimal setting I am using now as a norm. My gut tells me the minimal setting misses some decodes that I get with having a -90 noise floor but I cannot be sure.
                                            >
                                            > Warren Allgyer - W8TOD
                                            >
                                            > --- In softrock40@yahoogroups.com, David Turnbull wrote:
                                            > >
                                            > > On Thu, Jan 24, 2013 at 1:01 AM, Alan wrote:
                                            > > > I'm puzzled by your WSPR-IQ comment. Is this a fault in WSPR?
                                            > >
                                            > > WSPR doesn't seem to find signals that are more than 20dB away from
                                            > > it's arbitrary 0dB level. You can see them clearly in the waterfall.
                                            > > They just don't decode. If you do the OpAmp gain mods then the noise
                                            > > meter in the lower left always stays red with more than -20dB. By
                                            > > using HDSDR or PowerSDR, you can manually set the gain and turn off
                                            > > AGC. This VAC method seems to always outperform the I/Q mode anyways.
                                            > > I suppose if your line-in volume has gain instead of attenuation then
                                            > > you could fix it there too.
                                            > >
                                            > > 73 David AE9RB
                                            > > http://AE9RB.com/
                                            > >
                                            >
                                          • warrenallgyer
                                            I know.... I promised. You can commiserate with my ex-wife. Sorry. A comparison of the dynamic range of: 1) Griffin iMic USB adapter. 16 bits, 48 KHz only.$30
                                            Message 21 of 22 , Jan 26, 2013
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                                              I know.... I promised. You can commiserate with my ex-wife. Sorry.

                                              A comparison of the dynamic range of:
                                              1) Griffin iMic USB adapter. 16 bits, 48 KHz only.$30 Amazon.com
                                              2) Creative X-Fi SB Pro USB. 24 bits, 48/92 KHz
                                              3) Realtec internal audio card, 16 Bits 48/92 KHz MSI Netbook.

                                              All tests done at 10 MHz with RXTX 30/20/17.

                                              Griffin iMic
                                              Noise floor after S9 calibration: -129 dBm
                                              RF Input level for 1 dB compression: -11 dBm
                                              Useable Dynamic Range: 118 dB
                                              Practical Dynamic Range with antenna noise at -110 dBm: 99dB
                                              Note: Record input level on the PC control panel set to one increment above minimum.

                                              Creative X-Fi USB
                                              Noise floor after S9 calibration: -147 dBm
                                              RF Input level for 1 dB compression: -12 dBm
                                              Useable Dynamic Range: 135 dB
                                              Practical Dynamic Range with antenna noise at -110 dBm: 98dB
                                              Note: Input level is fixed on the PC control panel

                                              Realtec Internal Card
                                              Noise floor after S9 calibration: -139 dBm
                                              RF Input level for 1 dB compression: -13 dBm
                                              Useable Dynamic Range: 126 dB
                                              Practical Dynamic Range with antenna noise at -110 dBm: 96dB
                                              Note: Record input level on the PC control panel set to one increment above minimum.

                                              My conclusion: The expensive external 24 bit USB card represents no advantage whatsoever over the internal card in the Netbook, and this is how I operate; internal card for IQ in and out, cheap external card for speakers and mic.

                                              Caveats: I have seen internal cards that do not support stereo and do not support 92 KHz sampling, The stereo is an obvious non-starter and the 92 KHz is operator preference.

                                              Now I am really finished with this!

                                              Warren Allgyer - W8TOD
                                            • warrenallgyer
                                              (retrieved for a couple of touch-ups) I know.... I promised no more. You can commiserate with my ex-wife on broken promises. Sorry. This is a comparison of the
                                              Message 22 of 22 , Jan 26, 2013
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                                                (retrieved for a couple of touch-ups)

                                                I know.... I promised no more. You can commiserate with my ex-wife on broken promises. Sorry.

                                                This is a comparison of the dynamic range of:

                                                1) Griffin iMic USB adapter. 16 bits, 48 KHz only, $30 Amazon.com
                                                2) Creative X-Fi SB Pro USB. 24 bits, 48/96 KHz
                                                3) Realtec internal audio card, 16 Bits 48/96 KHz MSI Netbook.

                                                All tests done at 10 MHz with RXTX 30/20/17.

                                                Griffin iMic
                                                Noise floor after S9 calibration: -129 dBm
                                                RF Input level for 1 dB compression: -11 dBm
                                                Useable Dynamic Range: 118 dB
                                                Practical Dynamic Range with antenna noise at -110 dBm: 99dB
                                                Note: Record input level on the PC control panel set to one increment above minimum.

                                                Creative X-Fi USB
                                                Noise floor after S9 calibration: -147 dBm
                                                RF Input level for 1 dB compression: -12 dBm
                                                Useable Dynamic Range: 135 dB
                                                Practical Dynamic Range with antenna noise at -110 dBm: 98dB
                                                Note: Input level is fixed on the PC control panel

                                                Realtec Internal Card
                                                Noise floor after S9 calibration: -139 dBm
                                                RF Input level for 1 dB compression: -13 dBm
                                                Useable Dynamic Range: 126 dB
                                                Practical Dynamic Range with antenna noise at -110 dBm: 96dB
                                                Note: Record input level on the PC control panel set to one increment above minimum.

                                                My conclusion: The expensive external 24 bit USB card represents no advantage whatsoever in normal operations over the internal card in the Netbook.

                                                There is the potential to gain an additional 20 dB or so of headroom with the Soundblaster by adding RF attenuation or reducing the op amp gains, and resetting the software gains. However -11 dBm is more than 60 dB over S9 and that is normally sufficient even in severe overload conditions.

                                                Caveats: I have seen internal cards that do not support stereo and do not support 96 KHz sampling, The stereo is an obvious non-starter and the 96 KHz is operator preference.

                                                As I said before: Spend that expensive sound card money on antennas, whiskey, and roses for the wife. Better returns all the way around.

                                                Now I am really finished with this!

                                                Warren Allgyer - W8TOD

                                                Note defining my terms: "RF Input level for 1 dB compression". I found it hard to objectively compare the spurs and baseline disruption among the cards to determine similar levels of overload. Instead I got the input level in the region of overload and then, using the step attenuator, adjusted the RF input level until the indicated signal level stopped increasing. The level recorded was the last one dB increment which resulted in one dB increase in indicated level on HDSDR. Going one dB more gave minimal or no increase in the indicated level.

                                                --- In softrock40@yahoogroups.com, "warrenallgyer" wrote:
                                                >
                                                > Further to this and, hopefully, my final note on the subject,
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