schrieb Marcus D. Leech am 2011-01-12 02:40:
There is a lot of people outside the Linux world, especially in the
non-academic hobbyist corner. These people seem to me to try to work
with least possible changes, that is install no new OS, install no
additional tricky exotic drivers, and at most plug in some USB device.
That's perfectly ok for me. If these people should be serverd as well
you unfortunately _have_ to to think about Windows, as hard and painful
as it may seem.
Yup, I reluctantly agree. But I have to assume that UAC2 is the "future" of
USB Audio devices, and as such, should probably be the way to go forward.
I'm pretty sure that the USB consortium didn't invent UAC2 purely for
LInux users :-)
Now, to keep ideas ball rolling here:
So, by way of a start on a cheap(ish) receive chain block-diagram, I
whipped-up this:
http://www.sbrac.org/files/digital_receiver2.pdf
This has a "reasonable" RF Rx chain, and includes a "reasonable"
(20Msps) ADC.
The "trick" is that instead of doing decimation in an FPGA, you
select the correct
filter from the bank, and change the ADC clock rate. Discrete
passive filters are
reasonably easy to design and fabricate, and if there are only, let's
say, four of
them, covering 4 different desired SPS rates, that might be acceptable.
Also, the design "terminates" in an FMC connector, which allows you to
mate this up with
something like a Xilinx FPGA+1GiGe card, like the SP601 or similar.
If one desired USB instead, then a simple EZ-FX2 USB-2.0 card with an
FMC connector on it, and whatever
logic was necessary to grab samples from the ADC could be designed
and built.
A "wrinkle" in such a design is that one is at the mercy of the tuning
resolution of the down-converter,
since there's potentially no DDC (unless you implemented one on the
FPGA card).
--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
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