Resolution Filters

The first filter in the tinySA is the band pass filter of the 1st IF. It has a bit of an odd shape but it does a good job in removing the image that would otherwise reduce the sensitivity of the RX SI4432. The span is 10 times the largest resolution filter.

attachment:BPF.jpg

The tinySA resolution filters inside the RX SI4432 are implemented in DSP code. Here is the shape of each of the selectable resolution filters. The span is always 10 times the selected RBW. The side lobes are caused by spectral leakage in the DSP filter. The noise floor moves up with decreasing bandwidth due to the phase noise.

600kHz

attachment:RBW600.jpg

The side lobes are mostly removed by the 1st IF filter.

300kHz

attachment:RBW300.jpg

Also here the side lobes are mostly removed by the 1st IF filter.

100kHz

attachment:RBW100.jpg

As the side lobes now fit within the passband of the 1st IF filter they become visible.

30kHz

attachment:RBW30.jpg

10kHz

attachment:RBW10.jpg

The impact of the phase noise is visible with the noise floor moving up.

3kHz

attachment:RBW3.jpg


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TinySA-ResolutionFilters (last edited 2020-10-16 14:43:07 by RudolfReuter)