[hpsdr] Basic question

[Bob McGwier]

One of the single best design decisions in my opinion for HPSDR was to 
not cut a corner on the A/D for Mercury. Phil C. chose the LT2208 which 
has 90+ dB dynamic range running at 135 MSPS. This means that with 
reasonable filtering, even on HF, the near/far problem is much less of 
an issue than it has been in the past. Further, as you downsample 
significantly and downconvert in the Cyclone II on the Mercury board, we 
get significant processing gain. This will be one of those interesting 
cases where the IMD-DR (dynamic range) and blocking dynamic range will 
have a weird relationship. Mercury will provide a good HF receiver. 
Before recent trends, it would have been "the best there is". I agree 
with Phil H. We are pretty near to the time when we will hook the A/D to 
the antenna through a BPF and the difference between these High-Q direct 
conversion receivers will melt away. We are not there yet, but you can 
see it coming.

Bob
N4HY




Eric Blossom wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> On Mon, Sep 18, 2006 at 10:57:45AM +0800, pvharman at arach.net.au wrote:
>   
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> Hi Steve,
>>
>> We are actually going down both paths – have a look at the Horton and Phoenix 
>> projects on the HPSDR Wiki  at 
>>
>> http://hpsdr.org/wiki/index.php?title=HpsdrWiki:Community_Portal
>>
>> The reasons for doing Mercury are:
>>
>> 1. To see how good the latest ADCs are in comparison with ‘traditional’ 
>> analogue  SDR circuitry. 
>>     
>
> Also, the high sample rates enable all kinds of interesting wider-band
> experimentation.
>
> Eric K7GNU
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>   


-- 
Robert W. McGwier, Ph.D.
Center for Communications Research
805 Bunn Drive
Princeton, NJ 08540
(609)-924-4600
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