Now we’re getting somewhere.
SO, if you sample the voltage appearing at the output of a given RF input
stage, and it is, say, 2 uV after scaling for whatever gain is in the front
end, and the A to D LSB size.
If I leave that 2 uV signal (the one I am trying to hear) at the input, and
then apply 30 million microvolts (30 volts, which is143 dB over 2 uV) at
another in band frequency, I will not experience any digitization problems?
Gary
> On Sep 11, 2016, at 5:10 PM, Paul Christensen <w9ac@arrl.net> wrote:
>
>> "It still does not explain how you can digitize a signal with amplitude
> that is 140 dB signal above one LSB using a 16 bit A to D."
>
> You're incorrectly applying bit strength based on strictly on voltage. We
> cannot use the classic format for dynamic range where DR = 20 log2^ (bit
> strength). That gives 96 dB of DR for a 16 bit voltage based system where
> other factors like ADC clock rate and bandwidth are important.
>
> Example: the SunSDR Colibri receiver has a 14 bit ADC. Like all DDC
> receivers, it achieves its DR through the process of decimation and
> filtering. If a 14 bit ADC is sampling at 80 Msps with decimation occurring
> to a 500 Hz bandwidth, then there's an increase of DR by 10 log(80^e6/500).
> That's 53 dB. SunSDR uses an ADC used that's specified with a 77 dB SNR at
> 15 MHz. With decimation, the dynamic range is increased to 77 dB + 53 dB =
> 130 dB.
>
> How about a 16-bit receiver that's rated with a 77 dB SNR at 30 MHz. Assume
> the ADC is clocking at 125 Msps. 10 log(125^e6/500) = 54 dB. After
> decimation, DR is 77 dB + 54 dB = 131 dB.
>
> We gained only 1 dB of DR by going from a 14-bit ADC to a 16-bit ADC. This
> is exactly why folks have been saying it doesn't make a difference in nearly
> every amateur application. There may be other design factors to consider
> but DR isn't one of them. The ANAN-100B has nearly the same DR as the more
> expensive ANAN-100D. One product uses a 14 bit ADC, the other is 16 bit.
> Let's stop treating the subject like we're calculating the DR of a CD
> player.
>
> Paul, W9AC
>
>
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