Hi Joe,
Guess we will have to await independent testing. The Flex folks seem to
assert they have the equivalent of more than 24 bit when dealing with
adjacent strong signals.
From the Flex reflector...
> Just in rough numbers, you get a 1/2-bit for every divide-by-two decimation
> you do. If you are looking at dynamic range in a 500Hz bandwidth (this is
> what we typically do). The math I generally use to get there is
> log(f1/f2)/log(2)/2. I just think this way as a programmer (do everything
> in base 2). So if you take log(245.76E6/500)/log(2)/2 you get 9.4 extra
> bits when added to the 16 gives you 25.5 bits (152.7dB dynamic range).
> This assumes all 16-bits of the ADC are "good" which is probably not a
> good assumption. I'd have to pull out the notes and look at the data sheet
> again, but this should give you a rough idea. Hopefully I haven't made an
> additional "duh" today myself!
>
> Bottom line -- there's plenty of dynamic range.
>
> Also, if you are interested, we are using Xilinx DSP48E1 blocks which use
> an 18x25 multiplier and so Xilinx tools generate the on-board DDS as a
> 25-bit DDS by default --- again to preserve the SFDR of the receiver. We
> could add extra bits, but 25 are fine for the same reason.
>
> Steve
>
> Stephen Hicks, N5AC, AAR6AM
> VP Engineering
> FlexRadio Systems™
> 4616 W Howard Ln Ste 1-150
> Austin, TX 78728
> Phone: 512-535-4713 x205
> Email: steve at flexradio.com
> Web: www.flexradio.com
On 5/19/2012 8:11 PM, Joe Subich, W4TV wrote:
>
> Decimation can help but it is not a magic bullet that eliminates
> the effects of ADC overflow and/or blocking due to gain reduction.
>
> 73,
>
> ... Joe, W4TV
>
>
> On 5/19/2012 7:57 PM, Tom Azlin N4ZPT wrote:
>> decimation counts
>>
>> On 5/19/2012 7:29 PM, Joe Subich, W4TV wrote:
>>> The issue will be the severely limited dynamic range of the 16 bit
>>> ADC. Without effective AGC ahead of the ADC there *will* be overload
>>> problems on crowded bands (e.g. 160/80/40) where any transceiver must
>>> deal with many extremely strong ("local") signals while maintaining
>>> maximum sensitivity. With AGC, the strong local signals will cause
>>> "blocking" as the gain is reduced to prevent overflow of the ADC.
>>
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