[Discuss-gnuradio] Downsampling in GNURadio

Hi,

I would like to downsample a signal from 390,625 Hz to 125 Hz. What is the best way to do this in GNURadio?


Please find below some issues I am having with this.

First, I used the Low Pass Filter block, in GNURadio, I set my Decimation to 3125, my Cutoff Freq to 125/2. But I am not sure about the recommended value for the Transition Width parameter?

On another note, to obtain accurate results for downsampling in Matlab (and for DSP generally) it is often recommended to split the big decimation factor into a cascade of smaller ones. If I was to do the downsampling from 390625 to 125 Hz in Matlab I would do something like 5*5*5*5*5 (i.e., five separate downsamplers). How to optimally do this in GNURadio? By 'optimally' I mean with less computational resources given that I need to do this for multiple channels simultaneously.

Finally, in another experiment for testing downsampling in GNURadio, I tried to use the Rational Resampler block with the default settings. However, my results were aliased. I think Low-Pass Filtering is not included in the Rational Resampler by default. Is this right? How do I enable the low-pass filer? and what kind of filter is recommended?

Thanks in advance for your help.

Best regards,
Khalid