Wednesday, April 24, 2013

We receive 75-80% of the passband only !!

Reference :

No system is capable of using 100% of the nyquist bandwidth, and the USRP is no exception.

On receive, our passband is flat out to about 75 or 80% of nyquist.  

For 8 MS/s complex sampling, that gives more than 6 MHz of flat bandwidth. 

On transmit, there are no halfband filters in there, so you will see more rolloff from the CIC filters.

If this is a problem, you have 3 options:

-  If your generated signal is at less than 8 MS/s complex, then you
should just upsample in software.

-  If your generated signal is at the full 8 MS/s then you can
pre-distort your signal to compensate for the CIC rolloff.

-  Otherwise, I would suggest making a new FPGA image with halfband
filters in the TX side.  You can make room in there by removing one
receive chain (leaving only one).

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