[evlatests] VLA Test Meeting, R-L phase

[Vivek Dhawan]

Rick showed examples where most antennas had time variable R-L phase.
In those observations the RF band was changed very often, L,S,...Q.

I examined 2 datasets from recent pointing/baselines runs. These cover
the full Az/EL range over ~3 hours, without changing the RF band.

There is no significant R-L variation on most antennas. Exceptions are
ea19 at C band, about 15deg variation. (attached plot**). A-C and B-D
phase deviations are much the same.

At X band ea19 is clean, and the worst offenders are ea12 and 21, both
only ~5deg maximum variation, and not very often.

So, band changes are (somehow) driving the R-L phase change. Since the
most critical RF and LO coax switches have already been replaced, the
usual 'blame the switches' does not apply. Other ideas?

In many cases Rick showed, the variation tracked temperature (or pdif,
which tracks temperature). Keith Morris suggested cable length changes
with temperature, which could be unmatched between R and L, and have
the effect seen. To be tested...

---

** Caption: Blue= (A-C) phase. Red=(B-D). Antenna 19 is in the middle
of the page. X-scale +-20deg each antenna. Timerange 3 hours. Each
cluster of points is a different source/az/el, including over-the-top.

Rick Perley wrote:
>     The monthly VLA 'science/engineering' Test meeting will be held at 
> 10AM tomorrow (Thursday), 13 June, in Rm 317.  We have four items for 
> discussion (so far):

> 
>     3) Concerns obout R-L phase stability at high frequencies  (Rick)
-------------- next part --------------
A non-text attachment was scrubbed...
Name: R-L.X
Type: application/postscript
Size: 4216482 bytes
Desc: not available
URL: <http://listmgr.nrao.edu/pipermail/evlatests/attachments/20130613/49c10b34/attachment.ai>