Fractional Resampler block in GNU Radio has parameter phase shift but there is a lack of information in which factors user has to provide this parameter (radians, degrees or samples?). There is only an error message providing and info that the range of this parameter should be set between 0 and 1. I have created simple simulation with the fractional resampler block to kinda 'debug' its behavior. There is an 100 length input vector consisting of zeros but one in the middle (50th index). Then there is an interpolatior with the RRC filter. Given 0 phase shift and 1 for resampling ratio the output from the interpolating FIR Filter and Fractional Resampler are not in line, meaning that original signal is delayed by 3 samples and to compensate this phenomena I needed to delay samples by 3 in the branch where Fractional Resampler exists. Question are:
- Why 3 samples offset occurs?
- How to interpret phase shift parameter from Fractional Resampler block?
I don't know if its relevant information but QT Time Sink has normal trigger set to 0.1.
I am enclosing the flowgraph and the source https://gist.github.com/marcinsztajn/afe03d05653864b10125fefe7d8b888d