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Re: [Discuss-gnuradio] can I set bandwidth for rfx1800 board

From: James Jordan
Subject: Re: [Discuss-gnuradio] can I set bandwidth for rfx1800 board
Date: Wed, 29 Dec 2010 09:52:23 +0800


On Tue, Dec 28, 2010 at 11:43 AM, Marcus D. Leech <address@hidden> 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)

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

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