[hpsdr] General question - sampling rate vs bits on ADC

[Dr. David Kirkby]

This is a general question, about SDRs and the use of a suitable A/D.

If one uses an audio card, sampling rates are limited to about 196 kHz, but 
24-bit units are available.

In contrast, if one uses a faster card (say 100 MHz), the number of bits of the 
A/D decrease. Typically 14-bit, though there are some 16-bit cards.

What trade-offs does one get for an SDR? The audio card route is cheaper and 
gives more bits, so should I assume give better dynamic range. In contrast, I 
can see that with a faster sampling rate, the noise is spread over a wider 
range, so its lower in a specific bandwidth. But I would have thought the 
quantisation noise would be higher with the faster cards, as they have less bits.

I'm interesting in demodulation signal with bandwidth of <= 15 kHz, so even the 
audio cards easily meet the Nyquist criteria of a sampling rate of at least 
twice the bandwidth.


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