[TenTec] OT: Dynamic range of SDR Radios with 16-bit DAC

[Gary J FollettDukes HiFi]

So the clip point is 134 dB, not 140 dB.

Thus, a 134 dB above 2 uV signal, 10 KHz away from my desired 2 uV CW signal, will have no impact on my ability to receive that CW signal so long as I have selected a received bandwidth less than or equal to 10 KHz…

Right?

Gary




> On Sep 11, 2016, at 5:28 PM, Carl Moreschi <n4py3 at earthlink.net> wrote:
> 
> Sure you will have problems.  You have now exceeded the clip point.  For the Flex 6500 that's S9+80.
> 
> Carl Moreschi N4PY
> 58 Hogwood Rd
> Louisburg, NC 27549
> www.n4py.com
> 
> On 9/11/2016 6:26 PM, Gary J FollettDukes HiFi wrote:
>> 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 at 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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