[hpsdr] Selectivity design/measurement

[Robert McGwier]

I did all of these measurements on the alpha Janus and Ozy boards.  The 
AKM5394A is  one of the the  best recommendations I have ever given to 
any project or collection of projects and the Phil's and Bill and Lyle 
have a done a great job.   The Janus board lowers the noise floor of my 
SDR-1000 and that system is not SDR-1000 noise limited rather than Delta 
44 noise limited and the "hump" is gone on my set up where I used to 
have a hump with my Delta 44.  I never had one with the Lynx L22 and it 
uses the AKM5394A with balanced inputs. 

I am in Boston all week at Mercury computing for Cell processor 
training  and will be at Virginia Tech next week at the wireless group 
but I invite any of the other developers to feel free to publish the 
numbers Hambly and I measured in the lab using the SDR-1000 and with 
with the fancy audio generators.

Bob
N4HY


Lyle Johnson wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
>   
>> ...My question should have been much more specific, as:  "Has anyone built a 
>> receiver out of HPSDR components and if so have they done any selectivity measurements?"
>>     
>
> Janus+Ozy have been used with PowerSDR and an SDR-1000.
>
> The QSD A/D converter system will likely impact the minimum discernible 
> signal (MDS) unless there is a low-noise RF preamp in use.  It will most 
> certainly have a great impact on the dynamic range and distortion products.
>
> The selectivity is done in DSP and is pretty independent of the soundcard.
>
> Mercury prototypes have been built and are documented on the wiki.  The 
> don;t use a "soundcard" but instead do direct digital conversion of RF.
>
>   
>> I think your point about the DSP defining the selectivity means that the hardware components do not 
>> contribute or detract meaningfully from selectivity. Is this correct... 
>>     
>
> That is correct.  In more general terms, a bandpass filter is needed at 
> RF to limit the signals the SDR is exposed to.  The usual selectivity - 
> e.g., a 500 Hz CW filter, or 2.8kHz SSB filter -- is done in software 
> and shoudl not be materially affected by the hardware.
>
> Lyle
>
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>   


-- 
AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,
TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair
"Taking fun as simply fun and earnestness in earnest shows
how thoroughly thou none of the two discernest." - Piet Hine


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