On Thu, Nov 24, 2011 at 6:46 PM, Marcus D. Leech <mle...@ripnet.com> wrote:
> **
>
> Actually, I am not using any sinusoidal function in this measurement. So,
> zero values are not valid I think. I am mostly using the noise signal so I
> thought there must be a value.
> Here is a sample of what I got.
>
> Any idea would be highly appreciated.
>
> 0.0001220703 -9.1552734375e-05 0.0001831055 -6.103515625e-05
> 9.1552734375e-05 0 0.0001220703 -0.0001220703 0.0001220703 -0.0001220703
> 6.103515625e-05 -3.0517578125e-05 0 -6.103515625e-05 0.0002441406
> -6.103515625e-05 0 -6.103515625e-05 0.0002746582 0
>
>
Those samples look fine. And remember that '0' doesn't mean that it has to
be exactly 0; just a signal too small for the ADC to pick up of to have any
of it's bits toggled, so it will be 0 when sampled.
Tom
> How is it that you can be a masters student in electrical engineering,
> and *not* know that noise signals are simply the super-position
> of a large series of sinusoidal (or near-sinusoidal) functions? Once
> again, the ADCs in an SDR receiver are sampling a complex voltage.
> That voltage may occupy any values between {-adc_resolution,
> +adc_resolution}. In UHD, the ADC values are scaled (normalized)
> into the range {-1.0, +1.0} to make things within the flow-graph
> somewhat more general, and allow a certain amount of hardware
> independance.
>
> In general, the samples of a noise source will be equally distributed
> about 0, and in fact you can confirm this by calculating the
> running-average of all your samples--they will tend to converge to 0 (in
> practice, there will be a small amount of DC offset which
> will cause this convergence to be not exactly at zero).
>
> But all this should be in course textbooks, etc. The folks here are
> generally kind, and patient, but they can't hope to teach people entire
> courses in electrical engineering, RF design, linear and non-linear
> circuit theory, and digital signal processing. Although, those who
> *do*, generally charge money for it, in one way or another.
>
>
> --
> Marcus Leech
> Principal Investigator
> Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org
>
>
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