[esa-t474] BPM frequencies

[Mark Slater]

Just as a bit of an aside on the split frequencies of x7 and y7, I've had 
a brief look at these myself:

http://pcfj.hep.phy.cam.ac.uk:8080/slater/

entries 42 and 43. I'm going to try to make more headway here so we can 
actually get meaningful positions out of the BPM.

Thanks,

Mark


On Wed, 6 Feb 2008, Bino Maiheu wrote:

> 	Dear All,
> 
> As a first step in the analysis of the July 07 data, I've started by
> having a real close look to the frequencies of the waveforms as they are
> needed for the calibration of the BPMs and I want to understand any
> systematics as good as possible.
> 
> I've fitted every BPM waveform with a decaying exponential, using a
> constrained fit with the frequency and width of the fourier transform
> peak as initial input. This fit, although somewhat slow, seems to be
> working fine. 
> 
> The FFT spectra, frequencies etc are available from
> 
> http://www.hep.ucl.ac.uk/lc/T474/EsaData/fits.0/
> 
> where the fit parameters of each fit are stored in the root files as
> well. I'll upload macros into cvs later on to plot the fit functions on
> top of the waveform and FT. 
> 
> So far, I've plotted these frequencies versus pulse number and updated
> the data quality web-database with the plots. So far runs 2725->2850 are
> there, with the others on the way (takes about 50-60 hours for a single
> average run). I've made a cut on the chi2/ndf for plotting the
> frequencies, showing only 'decent' quality fitted frequencies. 
> As Yury and Zen figured out, we were running on internal clock, so I
> have taken this into account, the IF frequency values shown are in MHz
> ( note the fact that we were undersampling for all but BPM7 ).
> 
> http://www.hep.ucl.ac.uk/lc/T474/EsaRunInfo/show_dq.php
> 
> ( currently 2735 -> 2850 )
> 
> I'll make a plot of the average frequency per run with the error, but i
> will need to look a bit in detail since some of the distributions are
> not nicely Gaussian, so that I pick the correct frequency for accurate
> calibration of the DDC algorithm. 
> 
> One thing i noticed, see e.g.:
> 
> http://www.hep.ucl.ac.uk/lc/T474/EsaRunInfo/show_dq.php?run=2725&plot=7
> 
> is that the frequency for BPM 12/24 waveforms seems quite unstable, I
> suspect this to be due to changes in the LO for these channels. Also,
> once can clearly see a double frequency structure for BPM 7. 
> 
> Anyway, as I said, I'll determing the averages to use as input for the
> DDC from this as Mark learned that this gives the best resolution. I'll
> add the plots for the decay constants and t0 from the fits as well. 
> 
> I'll keep you informed of my progress.
> 
> Bino
> 
> -- 
>                                                   !!!!!
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