[hpsdr] Some things worthy of your attention

[Robert McGwier]

jeff millar wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Krister Wikström wrote:
>   
>> I think the present SDR-1000 3-board stack with separate audio and
>> control interfaces is not very elegant, to put it mildly. I can
>> understand the initial rationale for using a sound card for the A/D and
>> D/A conversion, after all most PC:s and all laptops have a sound card.
>> BUT, as it turned out, most sound cards aren't good enough, a fact that
>> rather negates the initial idea. We definitely need an all-digital
>> interface between the RF head and the PC, the sooner the better.
>>     
>
> Using sound cards provided a stop gap technology when the only decent 
> dynamic range came from parts with kHz bandwidths.  Now, A/D's with MHz 
> bandwidths (and the CPU's to process the data) make sound cards look 
> very limited.
>
> Fast A/D's also provide digital I/Q which completely eliminates analog 
> balance problems.
>
> So, just about any time now all the radios will have Digital I/O through 
> a common PC compatible Interface, could be either USB or Ethernet, but I 
> bet USB wins.
>
> jeff, wa1hco
>   
With the 200 kHz wide A/D's available in 24 bit packages such as the 
AKM5394A that is being used in Janus,  you will find it darn hard to 
ever get the instantaneous dynamic range that is achievable by these 
narrower band IF's  available from the QSD (and its variants) where you 
get something like 115 dB SFDR and NO NEED FOR ANALOG AGC IN FRONT OF IT 
in the narrow band voice grade channel applications.  No multi hundred 
MHz A/D can give this kind of performance because of the near/far 
problem so far as I have been able to find.    You can get increased 
dynamic range (not instantaneous) by getting processing gain through 
downsampling/filtering.    We are beginning to get interesting enough 
parts that we might come close to this with these 16 bit (very 
expensive) A/D's running at high bandwidths (such as Mercury, etc.). 

In the end,  the criticism of the SDR-1000 is misplaced.    Getting 
performance that rivals much more expensive radios out of a design done 
in a garage over a couple of years whilst talking to amateur radio 
breakfast buddies on every Saturday about it and then helping to foment 
the revolution we have seen it do and starting a major open source, open 
hardware initiative along with proponents of GnuRadio is not something 
to be dismissed without comment.  To me,  the SDR-1000 is one of those 
little miracles that continue to make life interesting.

If Gerald and Flex were to continue this form factor into future 
radios,  then I would say you have an argument. 

Bob


-- 
AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,
TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair
"If you board the wrong train, it is no use running along the
corridor in the other direction. " - Dietrich Bonhoeffer


 1167999892.0