Re: [Discuss-gnuradio] Re: "Open-Hardware"

[Moeller]

On 12.01.2011 20:22, Marcus D. Leech wrote:
> http://www.sbrac.org/files/digital_receiver2.pdf
>
The RF range is interesting, from 70 MHz to 2.2 GHz.
For USRP you would need 2 different boards to cover that range,
or invest much more money into the WBX transceiver.

> 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

If connected to a Xilinx board, FIR and decimation could still be done in the 
FPGA.

> 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.

This would be a very powerful combination and only $250 for the mainboard.
With "large" memory 128 MB & DDR2 memory controller, 32 DSP slices,
MicroBlaze processing  with MMU and FPU inside a Spartan-6.

>
> 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.

There's a cheap one here, with USB2 and Spartan3, only 70€ (<$100)
http://www.ztex.de/usb-fpga-1/usb-fpga-1.2.d.html
Or this one for 145€?
http://www.cesys.com/fpga/spartan/efm01_en.html

Do you think the FMC interface can be realized with the 52 Xilinx GPIO pins,
just with the specific FMC driver software?

> 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).

Is this really a problem? For spectral analysis this is only an axis shift.
For demodulation you would have to do some kind of adaptive doppler 
compensation and phase
tracking anyway. Could all this be done by continuously changing the DDC 
parameters over the wire?