[hpsdr] NPR of Mercury (was: Boat Anchors..PreAmps)

[Larry Gadallah]

Thanks Alex. This removes much of the confusion. Based on your chart,
I am quite surprised how little difference in potential performance
there is between the LTC-2206 and the LTC-2208.

On 6 June 2012 08:08, Alex VE3NEA <alshovk at dxatlas.com> wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> The maximum NPR of 85.4 dB quoted by Adam was computed [1] for an ideal
> 16-bit ADC whose noise floor of -98.09 dBFS [2] is determined solely by its
> quantization noise. Perhaps ideal ADC's were out of stock when Mercury was
> prototyped ;-) because the radio uses LTC2208, a real 16-bit ADC with a
> noise floor of only -78 dBFS [3]. This makes a huge difference as far as the
> NPR is concerned.
>
> I have re-computed the maximum NPR using the same equations as in [1], but
> taking into account the actual noise floor of the ADC. The new chart [4] has
> the same curves as in Figure 2 of [1], with two more curves added for the
> real ADC's. The theoretical maximum NPR that can be achieved with LTC2208 is
> 66.4 dB.
>
> For comparison, LTC2206-14, a 14-bit ADC used in Perseus, has a noise floor
> of -77.3 dBFS [5]. Its maximum NPR is 65.5 dB.
>
> The values measured by Adam do not indicate any excessive IMD in the preamp
> of Mercury. To the contrary, for some reason they exceed the theoretical
> maximum for a real ADC.
>
>
> References:
> [1] www.analog.com/static/imported-files/tutorials/MT-005.pdf
> [2] http://en.wikipedia.org/wiki/DBFS
> [3] http://www.linear.com/product/LTC2208
> [4] http://dxatlas.com/misc/npr.png
> [5] http://www.linear.com/product/LTC2206-14
>
>
> 73 Alex VE3NEA


-- 
Larry Gadallah, VE6VQ/W7                          lgadallah AT gmail DOT com
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