>"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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