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Re: using Spectrum Lab to measure amplitude and phase differences of a soundcard

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  • irbsurfing
    Wolf, Could you give me an example of the syntax to use to get the measurements into the watch window please. (1) amplitude difference in dB between L and R
    Message 1 of 5 , Jan 11, 2012
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      Wolf,
      Could you give me an example of the syntax to use to get the measurements into the watch window please.
      (1) amplitude difference in dB between L and R
      (2) Phase difference in degs between L and R.
      I'm sure its real easy - sorry!
      Andrew

      --- In SpectrumLabUsers@yahoogroups.com, wolf_dl4yhf <dl4yhf@...> wrote:
      >
      > Hi Andrew,
      >
      > This may sound trivial but trivial solutions are sometimes the best:
      >
      > Use SL's "time domain scope" in X/Y display mode. I.e. connect the left
      > input channel to the scope's "X deflection", and the right channel to
      > the "Y deflection" in analogy to old analog(!) oscilloscopes. If there's
      > no phase shift or similar, the result should be a thin line on the
      > scope. If there's a phase difference, the result turns into an ellipse
      > or into a circle. These 'Lissajous figures' are rather old, but easy to
      > use for broadband signals (such as your frequency sweep) :
      >
      > http://www.qsl.net/dl4yhf/speclab/tdscope.htm
      >
      >
      >
      > For phase measurements in narrow frequency ranges, use the 'amplitude
      > and phase meters' which are described here:
      >
      > http://www.qsl.net/dl4yhf/speclab/phase_amplitude_monitor.htm
      >
      > The results of these functions can be displayed in numeric form, or be
      > plotted as a graph in the watch list / plotter:
      >
      > http://www.qsl.net/dl4yhf/speclab/watchwin.htm
      >
      > The precision of the phase meter function depends on the FFT resultion.
      > Too much to be explained in a single email :o)
      >
      >
      > Greetings,
      > Wolf .
      >
      >
      > Am 11.01.2012 18:05, schrieb irbsurfing:
      > >
      > > Hi,
      > > I'd like to try and measure how close the left and right channels are
      > > of my Creative USB0202 sound card are in terms of amplitude and phase
      > > difference. I plan to feed it with a variable tone split to the two
      > > channels and manually sweep it over 1-90kHz (192kHz sampling). Is it
      > > possible to set Spectrum Lab up to read out the amplitude and phase
      > > difference between left and right please? To what precision can it
      > > measure?
      > > I've had a look at the user guide and I'm not quite sure how to do it.
      > > Many thanks,
      > > Andrew
      > >
      > >
      >
    • wolf_dl4yhf
      Hi Andrew, ... measurements into the watch window please. The already mentioned phase- and amplitude measurement functions, unfortunately, are not designed to
      Message 2 of 5 , Jan 11, 2012
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        Hi Andrew,

        you wrote:

        > Could you give me an example of the syntax to use to get the
        measurements into the watch window please.

        The already mentioned phase- and amplitude measurement functions,
        unfortunately, are not designed to measure *differences*. What they do
        is measure (and, if you want) plot phase and amplitudes of single
        'carriers' on well-known frequencies.
        I first thought that by subtracting the readings from L and R would make
        sense, but it doesn't (it cannot turn a narrow-band phase meter for
        coherent signals into a broadband *phase difference* meter.
        Thus the following example will be of little use for you:

        pam1( 1000, CW, 2, L1).phase : returns the phase of a 1000 Hz "CW"
        carrier, update cycle 2 seconds, on the LEFT input

        pam2( 1000, CW, 2, R1).phase : returns the phase of a 1000 Hz "CW"
        carrier, update cycle 2 seconds, on the RIGHT input


        Subtracting both will give a difference, but only for a signal at 1000 Hz.

        An alternative may be the 'colour direction finder' but it doesn't
        produce numerical output (only graphical).

        http://www.qsl.net/dl4yhf/speclab/colourdf.htm

        When configured for 'E-field antenna + 2 combined loops', it in fact
        measures and displays the phase difference over the entire spectrum (the
        phase is displayed as 'bearing').
        The function call azim(1000,2000) will return the azimuth (in this
        antenna configuration that's the phase difference) of the strongest
        signal between 1000 and 2000 Hz. But there's no way to retrieve the
        numerical amplitude difference in this mode.

        As you see, it's not that easy...

        Cheers,
        Wolf .
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