[evlatests] LBR noise cal filter tests

[Paul Demorest]

PS, I meant to mention that these tests were made much easier due to a 
custom executor version provided by Ken that allows the state of the 
low-band cals to be controlled from the observing script (rather than me 
having to run a shell command by hand at the appropriate time).  Thanks 
Ken!

On 2017-04-25 10:18, Paul Demorest wrote:
> hi all,
> 
> This is an update on the effect of the low-band noise cal (aka
> switched power) system on L- and S-bands (see various old emails from
> me to evlatests about this).  Note that currently the low-band cals
> are turned off during all non-low-band observations, so this is not an
> ongoing problem.
> 
> Last week, Wes and co. installed some extra filters into the low-band
> systems on ea09 and ea11 to see if this effect could be reduced via a
> HW fix.  To test this, I took some new data both before (2017/03/30)
> and after (2017/04/24) the filters were installed.
> 
> The short answer is that the filters do not really seem to have
> helped.  The pattern of power vs freq does not look exactly the same
> as it did before, but the effect is clearly still there.  ea09 may
> even look a bit worse after this work.  I don't know what (if
> anything) this tells us about the nature of the problem.  Any ideas?
> 
> For those who want to see the data, the attached PDF shows the results
> from the two S-band tests for all antennas where data were taken.  The
> quantity shown is the ratio of "on-off" power at 10 Hz when P-band
> cals are switching to when they are off, as a function of frequency.
> S-band cals were switching the entire time, so ideally we want to see
> a flat line with a value of 1.0 (ie like ea04 which for some reason is
> not showing this effect currently).  This was measured using
> binning-mode widar autocorrelations.
> 
> Most antennas show nearly identical results in the two tests, so this
> effect is apparently stable over few-week timescales.  The power vs
> freq pattern clearly changed for ea09 and ea11, presumably as a result
> of the filter work.  It also changed for ea01 and ea16.  Maybe there
> was some other work on the low-band systems on these antennas during
> this time range?
> 
> I also took L-band data but it turned out not to be very useful due to
> a bug in the data recording software.  ea09 and ea11 still do show a
> strong effect at L-bang though.
> 
> Cheers,
> Paul
> 
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