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This screen allows the bunch by bunch filters to be configured. Normally the shape of the filter is automatically configured from the :CYCLECYCLES_S, :LENGTH_S, :PHASE_S settings, but the FIR can be written to :TAPS_S instead if :USEWF_S is set to "Waveform".
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| Name | PV | Description |
|---|---|---|
| FIR freq/size | :FIR:n:CYCLECYCLES_S, :FIR:n:LENGTH_S | These two determine the fundamental shape of the FIR, which is a sine wave with :FIR:n:CYCLECYCLES_S cycles in :FIR:n:LENGTH_S samples. These two numbers need to be adjusted so that the tune frequency is comfortably close to the ratio cycles/length. |
| Phase | :FIR:n:PHASE_S | This adjust the phase of the FIR and so determines the feedback phase. |
| Setup | :FIR:n:USEWF_S | Can be either "Settings" or "Waveform". If this is set to "Waveform" then the settings above are ignored and instead :FIR:n:TAPS_S is used to define the filter. |
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Finally, the FIR waveforms can be viewed and configured by clicking on the Bunch by Bunch FIR Waveform Control buttons.
Not related to software, but it is nice these filters can be externally verified with a VNA. Measure S-parameter from ADC to DAC:
1) transverse filter: sweep shows exactly one revolution bandwidth, bright yellow FIR 2/8, dark yellow FIR 1/8, blue straight trough.
2) transverse filter FIR 2/8, now with wider sweep, showing repetition every revolution harmonic.
3) longitudinal filter FIR 2/8 with decimation 10. Same sweep as above, filter passbands move closer together around revolution harmonics.