Thanks. On Tue, Dec 28, 2010 at 11:43 AM, Marcus D. Leech <[email protected]> wrote:
> 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 > > >
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