Experimental Test Data of the Direct RF Sampling Processor for SHINE Cavity Monitors

The beam tests were conducted at the end of the linac section of the Shanghai Soft X-ray Free-Electron Laser (SXFEL) under typical operating conditions (bunch charge ~500 pC).The dataset includes:Raw ADC sampling data: Time-domain waveforms (4096 samples per bunch pulse) and corresponding frequency spectra acquired by the direct RF sampling processor via under-sampling, with the 3.52 GHz cavity signal shifted to 285.9 MHz.Amplitude and phase extraction results: Derived using a fixed-point Goertzel-DFT algorithm.

Data include amplitude/phase errors as functions of DFT accumulation points around the peak and different data subset lengths (500–4000 points), used to optimize the processing parameters.Band-pass filter (BPF) necessity evaluation: Comparative measurements with and without an external 3.52 GHz cavity BPF in the signal path, showing that the BPF does not improve performance (amplitude error 1.29×10⁻⁴ and phase error 9.0 fs without BPF vs. 2.25×10⁻⁴ and 12.6 fs with BPF).Performance comparison of RF conditioning modules: Side-by-side comparison of the direct RF amplifier module (gain 24.8 dB, NF 2 dB) and a traditional down-conversion module (gain 22.7 dB, NF 7.5 dB), with both feeding into the same digitizer.