Forum: GNU Radio unknown attenuation after analysis filterbank

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feldmaus (Guest)
on 2009-05-15 16:39
(Received via mailing list)
Hi Gnuradio folks,

i am analysing the spectrum from 1MHz to 2Mhz. I splitted this Spectrum
into 3 parts:
1MHz - 1,333MHz
1,333MHz - 1,666MHz
1,666MHz - 2MHz

Therefore i used the Analysis Filterbank. Because i am searching for si
function
in the time domain as a response of a peak in the frequency domain, i
want
to use a band pass filter in the Analysis Filterbank.
Do i have to use the band pass filter or can i sill use the low pass
filter.
The response should be another one by using the Low pass filter ?

But my main Problem is, that my signal goes down in the second and third
band.
I doesn't know why.

Here is my Flow Graph:
Usrp Source --> Analysis Filterbank+Band pass filter --> Selector -->
fft sink graph

My band pass looks like this:
samp_rate=1e6
Intermediate Frequency of the usrp= 1MHz
firdes.complex_band_pass(1.0, samp_rate, samp_rate*0, samp_rate*1/3,
samp_rate*0.01)

Any hints how to correct this ?
Did i anything wrong ?

regards Markus
Brian P. (Guest)
on 2009-05-15 19:42
(Received via mailing list)
On Fri, May 15, 2009 at 8:18 AM, feldmaus <removed_email_address@domain.invalid>
wrote:
> to use a band pass filter in the Analysis Filterbank.
> My band pass looks like this:
> samp_rate=1e6
> Intermediate Frequency of the usrp= 1MHz
> firdes.complex_band_pass(1.0, samp_rate, samp_rate*0, samp_rate*1/3,
> samp_rate*0.01)
>
> Any hints how to correct this ?
> Did i anything wrong ?

So you are looking at 1MHz of spectrum with a sample rate of 1Msps
complex centered at 1MHz coming in from the USRP?  Or do you receive a
complex stream directly from the USRP at baseband?

The CIC filter has roll off which could be your culprit?  Do you have
a spectral plot of your bands as well as the entire incoming spectrum?

Brian
feldmaus (Guest)
on 2009-05-17 00:00
(Received via mailing list)
Brian P. schrieb:

> So you are looking at 1MHz of spectrum with a sample rate of 1Msps
> complex centered at 1MHz coming in from the USRP?  Or do you receive a
> complex stream directly from the USRP at baseband?
I am looking from 1MHz to 2MHz, therefore i set up the frequency
in the Usrp to 1MHz and the samp_rate to 1Msps(1MHz Signa Bandwidth).


>
> The CIC filter has roll off which could be your culprit?  Do you have
> a spectral plot of your bands as well as the entire incoming spectrum?
i will watching this next monday.

thanks and regards markus
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