[hpsdr] DDC Noise Figure

[Edson Pereira]

Hello,

I have been trying to educate myself about SDR using direct sampling and am
having some difficulty in understanding how to calculate the noise figure of
a DDC based SDR system. Since the noise figure takes into account the
bandwidth, would it be correct to say that even though the noise figure of
the ADC is high, the total noise figure of the receiver system can be
improved (by the various decimation stages)? Putting a pre-amp in front of
the ADC would seems to help considerably, at the cost of lower dynamic
range, but if my understanding is correct, the total noise figure will be
much better than that of the ADC alone. Could anyone shed some light? Some
math will be ok.

73,

-- Edson, pu1jte, n1vtn, jf1afn, pu2mwd
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