[Discuss-gnuradio] USRP decimation filter performance

[Richard Meston]

Hi all

 

Is there information anywhere about the performance on the USRP decimation filter?

 

I have a setup with an external radio which has a bandwidth of 5MHz around a 10.7MHz IF.  I think the attenuation of the radio is quite poor relatively far away from the 10.7MHz centre (e.g. -20dB at +/-10MHz).  

 

If I use the USRP with a decimation of 8, I should get a bandwidth of 8MHz (minus the filter roll-off) I assume – is this correct?

 

If so, then I’m worried about images in my passband – i.e a signal at, say, 18.7MHz will wrap around and be right in the centre of my passband, but attenuated by 20dB by the radio itself.  I assume there is attenuation from the decimation process (the CIC/half band filter) – can anyone give me an idea of how much decimation I can expect outside of my passband? (or put me right if I’m completely wrong with all of this!)

 

Thanks for your help

 

Rich