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hirose.chiaki - 23:35 Sunday 05 June 2022 (21025) Print this report
Comment to TF measurement of RFQPD for WFS on the REFL (20983)

With K.Tanaka and Tamaki

We performed transfer function measurements and phasing on the QPD from Monday to Thursday last week.
We summarised their setup and results.

TF measurement of RFQPD

The degrees of freedom are WFS_RFQPD{1,2}_seg{1,2,3,4}.
Measurements of the transfer function of the RF QPD were superimposed when using the AM laser and when using the test.
TF for all degrees of freedom are different in magnitude, but the waveforms are almost the same.
The QPD1 is discussed in 20983. However, due to the strong low-pass filtering in the digital system, the 45 MHz information disappears, so it is not necessary to consider it.
With QPD 2, it is peak at the frequency we want to see and not at the other frequency. So there is no problem with signal acquisition.

RFQPD phasing

In the 17 MHz band, the frequency of the function generator was set based on 16.873935 MHz, plus the frequency for the beat.
In the 45 MHz band, the frequency of the function generator was set based on 44.997157 MHz, plus the frequency for beats.
When the beat signal was viewed in the power spectrum, power was seen at the frequency added to the reference frequency. The phase difference of segments 2-4 with respect to segment 1 was measured and set on the MEDM screen.
The result was a phase difference of 1 or less.

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