Re: [Discuss-gnuradio] maximum of bandwidth and negative frequencies

[Karthik]

On Fri, May 29, 2009 at 6:50 AM, feldmaus <address@hidden> wrote:
> Hi All,
>
> I am using a usrp1, and an Analysis Filterbank with 3 bands. My IF is 1MHz.
> The decimation is 64, therefore i get 64MHz/64=1MHz bandwidth.
> Therefore i should see signals from 1MHz to 2MHz.
>
> I used a band_pass filter in the Analysis Filterbank, but my signal goes down 
> by
> ~1.6MHz.
> I am not sure why ?
>
> Is this because the half of the bandwidth is for the negative frequencies ?
>
> Here are my parameters again:
> decim=64
> samp_rate=64e6/decim
> firdes.band_pass(1.0, samp_rate, samp_rate*0.01, samp_rate*1/3, 
> samp_rate*0.01)
>
> Regards Markus
>

If you are tuning your usrp to 1 MHz and have a decimation of 64,
won't you be receiving signals from 0.5MHz to 1.5MHz?

Have you compensated for the cic filter droop in the passband? You can
use the filter design toolbox in matlab to design one. Here is an
example from Matlab
http://www.mathworks.com/products/filterdesign/demos.html?file=/products/demos/shipping/filterdesign/ddcfilterchaindemo.html

Hope that helps.

Karthik