Re: [Discuss-gnuradio] digitizing a digital data stream with USRP2

[Matt Ettus]

> I'm not intimately familiar with GNU radio hardware and the experts here will 
> hopefully correct me if needed, but I
> think you would face these issues:
>
> 1) The default FPGA logic doesn't offer a demodulation enable/disable, so you'd 
> have to make some logic changes and
> rebuild.

no changes are necessary.  He can just set the tuning frequency to 0.

> 2) Assuming the A/D converters on the LFTX and LFRX are>  8 bits and<= 16 bits, 
> then the maximum sampling rate you
> could move over GbE would be around 60 MHz.  Is that enough for your 
> application?  If you need faster rates but only
> in bursts (like a radar situation) then possibly some memory (block RAM) in the 
> USRP2 FPGA could be used for buffers.
> I'm not sure how much is available... a build without demodulation would 
> probably free up some mem.

There are no AD converters on the daughterboards, they are on the 
motherboard.  And they are 14 bits.

> 3) Continuous streaming to HDD file could be difficult, or at least would 
> require careful configuration of the HDD
> file system, real-time scheduling and other system considerations, and of 
> course careful programming.

We suggest turning off journaling in the filesystem.  If that isn't 
enough, an SSD or RAID should be able to keep up.

Matt