Stephen Arbogast has noted an error in the BAA GNU Radio for Amateur Radio Astronomy meeting last Monday and sent me the following information:
A rational re-sampler block does not change the frequency. Instead, it allows one to resample the source data stream by a ratio.
The Rational Resampler in GNU Radio is a DSP block used to change a signal’s sample rate by a precise fractional (rational) factor:
It performs two primary operations in a single block:
- Interpolation = Increases the sample rate by inserting zeros between every sample.
- Decimation = Decreases the sample rate by keeping only every nth sample.
Because inserting zeros creates unwanted spectral images, and decimating without filtering causes aliasing, the block uses a custom low-pass anti-aliasing/anti-imaging Finite Impulse Response (FIR) filter.
Key Parameters
- Interpolation = The factor by which the input rate is multiplied (upsampling).
- Decimation = The factor by which the output rate is divided (downsampling).
- Taps: The coefficients for the internal low-pass filter. If left blank, GNU Radio automatically calculates taps based on the cutoff frequency.
- Fractional BW: Defines the fractional bandwidth of the prototype filter (usually left at the default of