On 12/27/2010 10:31 PM, James Jordan wrote: > Thanks. So RFX board always capture a 20MHz bandwidth signal? But > applications use > RFX board such as openbts need only 200Khz bandwidth signal, why it > can directly use > the signal from RFX board? > Actually, the total bandwidth is 40MHz, due to complex (quadrature) sampling.
Most of the filtering is accomplished digitally, with the work in most applications divided between the USRP FPGA (decimation is also filtering), and whatever filtering is performed in software on the host. The set_bw() function exists to improve analog filtering prior to digitization, but it's usually superfluous, since the drivers will set the card up with a baseband filter that is appropriate to the sampling rate of the motherboard (64Msps for the USRP1, and 100Msps for the USRP2). In quadrature sampling, the analog baseband filter is generally arranged so that the low-pass cut-off is somewhat below the nyquist limit. -- Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
