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

[Carl Moreschi]

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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