Re: [Discuss-gnuradio] USRP2 + WBX How to use a 32 MHz signal band?

[Marcus D. Leech]

On 11/30/2010 07:04 PM, Vladutzzz wrote:
> I am interested in this 2 USRPs approach since I don't have the experience
> and the knowledge to start messing about inside the FPGA firmware code and
> have an extra USRP2.
> How would this go?
> I tried looking up some info about this topic. I've read some bits and
> pieces on a few forums. Most of the info is about having one USRP2 module as
> a transmitter and the other as a receiver.
> I want them both to be receivers(actually half a receiver) and to complete
> each other by receiving half of the 32 MHz band (so each would receive 16
> MHz).
> How would the USRPs be connected to the same computer? (MIMO cable?)
> How will the two 16 MHz bands be attached together to form the 32 MHz one
> (some kind of 2:1 multiplexing - I'm just guessing here)?
> I am aware of the great load exerted upon the system resources, but I'm
> trying to make this work anyway.
> Thanks.
>
> Vlad.
Assuming that you have a big-arsed machine to do this with, here goes:

Assumptions

  o phase-coherence between the two isn't an issue (if you're just 
doing power measurements, it won't be)
  o you have a very-studly computer
  o you have two good 1GiGe interfaces

Start out with two single-usrp sources, address them as appropriate for 
your two USRP2s.

16MHz isn't an available bandwidth out of the USRP2, so use 16.66667MHz, 
and band-limit it to exactly 16MHz with an FIR bandpass filter.
Your two USRP2s will each be tuned to a frequency that is 16MHz away 
from each other.

Once you have your two band-limited complex signals, detect them, using 
a complex-to-mag-squared on each of them.
  Then put the two signals into an adder, and low-pass filter with a 
single-pole IIR or FIR low-pass filter.  Decimate to taste
  after filtering.


--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org