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

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] USRP2 + WBX How to use a 32 MHz signal band?
Date: Tue, 30 Nov 2010 23:08:36 -0500
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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
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.

Assuming that you have a big-arsed machine to do this with, here goes:


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

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