[USRP-users] Basic Questions about DDC and Sampling Rate

Alex The Great achillesmagnus at gmail.com
Thu Jun 14 18:04:11 EDT 2012

Hi, I'm having trouble with the basics here.
I'm using the N210 with the SBX daughterboard.

Please tell me if my logic is correct:
The USRP N210 has 100 MHz bandwidth.
I can decimate at a minimum of 8, and at a maximum of 256.
Thus the maximum amount of data I can send from the USRP to the PC is 100e6
/ 8 = 12.5 Msps.
The minimum is therefore 100e6 / 256 = 390.625 ksps.
If my samples are 4 bytes large, then the min and max amounts of data being
sent to the PC is 1562.5 kBps and 50 MBps.

I am still not understanding how these factors come into play:
Is there a minimum amount of data that must be sent from the USRP to the PC
per second?
How does the sampling rate relate to decimation in the DDC?
The maximum sampling rate is 25 Msps (determined by the GigE interface?).
The SBX has 40 MHz bandwidth. Does this mean that out of the 100 MHz
bandwidth of the USRP, only 40 MHz is usable?

Please correct me in any place I am wrong.
Sorry for the newbie questions, but I really want to understand.

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