[evlatests] Phased VLA + H-maser : all good.

[Vivek Dhawan]

Today another short VLBI fringe test showed the VLA, with H-maser as
timekeeper, to be working well.

VLA +25.2 usec offset and ~0 rate referenced to PieTown, same test
conditions as yesterday (below) except H replaces the Rb clock.

The GPS-CLK1 monitor is <1us, and the extra offset of about +25 us
is in the same ballpark as yesterday.  Most likely this is a feature
of the different filters in the VLA and VLBA (meaning WIDAR and RDBE)
at 1MHz BW.

Onward to science tomorrow!



Vivek Dhawan wrote:
 > Hi Keith,
 >
 > todays' short test shows the following:
 >
 >       Rb, at 01 UT MJD 56420 = 7pm May 7th:
 >
 >  From VLBI (vs. MK)         +115 usec, rate +5.2e-10 s/s = 45 us/day.
 >  From L356 clock #1 vs.gps:  +88 usec, rate +5.2e-10 s/s
 >
 > The rate is right on the money. The offset is a little off, but it
 > is in the realm of what we got on 'good' days (i.e. within ~20usec).
 > This was a 1MHz narrow band experiment, and we know there is a BW-
 > dependent delay offset which might be VLA or more likely VLBA filter
 > delays. So I am in a state of tentative belief in the L356 monitor.
 >
 >
 >
 >       H maser, at 01 UT MJD 56420 = 7pm May 7th:
 >
 >  From L356 clock 1 vs.gps:  offset (+1s - 0.7us), just under 1 sec.
 >                                                     rate near zero.
 >
 > Is the ~1sec understood? Will it be removed before synch?. If so
 > I think the H-maser can go in tomorrow.
 >
 >
 >
 >
 > Keith Morris wrote:
 >> We have been monitoring and adjusting the drift rate of the Maser since
 >> it was installed at the VLA site two weeks ago.  A frequency adjustment
 >> was made yesterday morning, and the drift rate since then is
 >> unmeasurable at the resolution of this monitor point, which means less
 >> than 8ns/day.  More importantly, the rate appears to be stable.  I
 >> recommend that we switch the system back to Maser during tomorrow's
 >> maintenance day.
 >>
 >> This means that we will need to resynchronize, since the difference
 >> between the maser offset to GPS and the rubidium offset to GPS will
 >> likely be greater than the sync detect window in the L350.  Presently,
 >> the Rubidium offset to GPS is around 76us (leading), and the drift is
 >> accelerating.
 >>
 >> If anyone objects to this, please let me know.  Otherwise we will
 >> proceed tomorrow.  If it is decided that we should *not* make the
 >> switch, then I would recommend that we make another frequency adjustment
 >> to the Rubidium.  I am coordinating with Kerry to avoid conflicts with
 >> the correlator testing.
 >>
 >>
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