[hpsdr] Selectivity design/measurement

[Mark Amos]

Lyle,

Thanks for the quick reply!   My question should have been much more specific, as:  "Has anyone built a 
reciever out of HPSDR components and if so have they done any selectivity measurements?"

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, or did you mean something else? 

In any case, sorry for the overly broad question and thanks for all the great work.  This is an historic 
moment in time, and I'm happy to be living in it.

Mark



------- Original Message -------
>From    : Lyle Johnson[mailto:kk7p at wavecable.com]
Sent    : 2/15/2007 10:39:51 AM
To      : mark.amos at toast.net
Cc      : hpsdr at hpsdr.org
Subject : RE: Re: [hpsdr] Selectivity design/measurement

 > I've done some searches and haven't been able to find any information on selectivity of the 
> HPSDR (either design goals, or actual measurements with beta hardware.)
> 
> Can any body point me in the right direction?

There may be a misconception here.  There is no "HPSDR" in the form of a 
final product like, say, an SDR-1000 or an SDR-14.

HPSDR is a collaborative effort to create building blocks from which you 
can create your own SDR, tailored to your needs/ wants/ desires.

The initial mostly-hardware building blocks are the ATLAS backplane, Ozy 
USB interface + FPGA development board, Janus high-performance A/D and 
audio interface, and Pinocchio extender card.

Ozy and Janus in particular will support the SDR-1000, softrocks, etc. 
If the radio is QSE/QSD based, Ozy+Janus should provide very good 
performance.

Selectivity will be a matter of the DSP back end.  Currently, Ozy+Janus 
are running a modified version of PowerSDR.  As you've noted on the Flex 
reflector, the displayed graphic of filter bandpass and the realized 
selectivity are not necessarily the same.  The filter graphic, in 
particular, appears based on calculation sent downstream for further 
processing, *not* measurement of the resultant filter based on other 
parameters, such as block lengths and so forth.  Keep in mind that the 
PowerSDR display GUI is just that - a GUI.

In any event, the HPSDR project will be creating and delivering direct 
digital exciters and receivers, as well as improved QSD and QSE boards. 
  There is also a low-power, portable QSD/QSE based device, Odyssey, 
whose initial application will be SuitSat2.

Lots of exciting things happening, dig in and enjoy!

73,

Lyle KK7P





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