[Discuss-gnuradio] unknown attenuation after analysis filterbank

[feldmaus]

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