http://www.sbrac.org/files/digital_receiver_cheap.pdf
This has everything in one place--commit to a single host I/O, and go
cheaper as a result.
The estimated BOM cost for this, including PCB would be under $100.00.
If you sacrifice very-fine tunability, then you don't need a DDC in the
FPGA, and only need
a CIC decimator chain, and you only need Rx logic in the FPGA, so you
can get away with
the smaller EP1C6 FPGA. There's a 9K-LE Xilinx Spartan-6 which is
marginally cheaper
($16.44 vs $17.50) than the Altera, but only available in larger
quantities from Digikey.
Also, I think the Altera toolchain is cheaper (free??) -- I dunno, I'm
not an FPGA guy.
Note the use of ultra-cheap 8-bit ADCs. This design isn't going to win
any awards for
dynamic range, but it helps keep the BOM cost down, and as someone
else observed, you
get processing gain every time you reduce the bandwidth. So at 5MHz
bandwidth, you've
added a couple of effective bits. For the types of wide-band
science-radio experiments
one might want to do with this, a handful of bits is just fine.
Now, I want to emphasize again that I have *no interest* in physically
producing such a thing,
but I'm always willing to contribute my engineering wisdom, for
whatever that's worth.
Also, to set a ground rule for future discussions. If this turns,
yet-again, into an Ettus-bashing
fest, I'm dropping out of the thread, and not participating in any
further discussions. Such
nonsense isn't productive, or even fair or reasonable. Matt and his
employees (and part-time
contractors, like me) are good, hard-working people with an excellent
product, and who have
**pioneered** reasonably-priced hardware that works well with Gnu Radio.
The question I think this discussion can answer is fairly simple: are
there design choices that can
be made, with significant compromises in functionality, that can
produce a design that is practically
producible by an open-source hardware community, and will such a
device be useful-enough over
the types of hobbiest uses-cases we're interested in. Further, will
such a device meet the
delivered-price goals.
If the answer to the above is "yes", then the next question is: is
there a community of interested
volunteers to bring the project to fruition? Such an interested
community would involve:
o High-level hardware design
o Detailed schematic capture and PCB layout
o FPGA firmware design
o Host-interface (FX2?) firmware design
o Host driver software design and implementation
o Small-scale financial investment for initial PCBs, components, etc
Once such a board works, then someone needs to be found to distribute
either kits or finished product.
Something that vaguely compares to this effort is the FunCube Dongle,
which is a quadrature
receiver covering 64MHz to 1.7GHz, but with 96KHz host-side bandwidth.
That project is
selling fully-built units for about USD 170.00.
--
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
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