[USRP-users] DBSRX2 daughterboard bandwidth problem!!

Jason Abele jason at ettus.com
Mon Feb 13 17:41:55 EST 2012


On Mon, Feb 13, 2012 at 03:08:47PM -0500, mleech at ripnet.com wrote:
>   
> 
> Actually, I think I may have mis-spoke. It looks like the initial
> setting of bandwidth is fixed at 80MHz, which is fine for 100Msps
> baseboards, but not lower-sampling-rate ones. 
> 
> Ideally, you want it set
> at: 0.8 * baseboard-sampling-rate or thereabouts. 
> 
> Perhaps Josh/Jason
> could comment on this. 
> 

Seems like an ok idea for the defaults on DBSRX*, we'll set the default
to low-pass bandwidth to 0.8*codec_rate (ADC rate) for anti-aliasing
regardless of which motherboard is used.  Update will be on master in a
few days or less

I don't think it makes sense for the other daughterboards with
configurable analog filtering, as they are all less than the default
codec_rate/2.0 on any motherboard.

If the user has the sophistication/need to change codec_rate, they can
probably change analog bandwidth of the daughterboard as best suits
their application.

Josh and I agree it definitely should not be tied automatically to the
sample-rate between USRP and host, as it would side-effect too many of
the users other settings every time they change sample rate, center
frequency, lo_offset, etc.  The user is free to set the bandwidth as
needed for their application in these cases.

Jason

> You can of course do this in your app, but it's
> nice if the driver "did the right thing" automagically. 
> 
> -Marcus 
> 
> On
> Mon, 13 Feb 2012 14:39:59 -0500, mleech at ripnet.com wrote: 
> 
> > Note that
> UHD normally sets the analog bandwidth of variable-analog-bandwidth
> cards (TVRX2/DBSRX/DBSRX2) to whatever is appropriate for the sampling
> rate of the front-end (64Msps B100/USRP1/E100 and 100Msps for
> N2XX/USRP2). 
> > 
> > Unless you have some very special situation in which
> you don't trust the digital filtering in the FPGA, you shouldn't ever
> have to set the analog bandwidth of the DBSRX2. 
> > 
> > -Marcus 
> > 
> > On
> Mon, 13 Feb 2012 19:27:42 +0000, Mike McLernon wrote: 
> > 
> >> Hi Ruth,
> 
> >> 
> >> Have you seen the following link? 
> >> 
> >>
> http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/2011-September/002415.html
> [1] 
> >> 
> >> Mike 
> >> 
> >> FROM: usrp-users-bounces at lists.ettus.com
> [mailto:usrp-users-bounces at lists.ettus.com] ON BEHALF OF Ruth Sancho
> >>
> SENT: Monday, February 13, 2012 9:31 AM
> >> TO:
> usrp-users at lists.ettus.com
> >> SUBJECT: [USRP-users] DBSRX2 daughterboard
> bandwidth problem!! 
> >> 
> >> Hi! 
> >> 
> >> My USRP N210 is working properly
> with the DBSRX2 daugtherboard. I am trying to make some simulations
> using Matlab. Could someone tell me how I could change the capture
> bandwidth? 
> >> 
> >> Thanks in advance. 
> >> 
> >> Ruth Sancho.
> 
>  
> 
> 
> Links:
> ------
> [1]
> http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/2011-September/002415.html

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