Tapasi received 3 emails from ed himwich
back in 2011 related to his commissioning of the goddard gsfc
12meter antenna:
Hi,
The elevation axis continued to show creep this
weekend. I have attached
a time-plot of the data which was collected for about
36 hours. The
general impression I get from the plot is that it
stable, maybe shifting
up a little, during the first daylight period (first 12
hours
(daylight), then overnight (middle 12 hours) it is
shifting rapidly, and
then in the next daylight period (last 12 hours) it is
more stable, but
still shifting up a little. It appears to have shifted
about 0.1 degrees
in the overnight period.
This is not inconsistent with the idea that something
is loose and that
differential contracting with cooling overnight makes
it looser. It
isn't obvious though why the change appears to be
monotonic, but maybe
there is some feature of the surface contact that makes
it ratchet.
The AuScope folks in consultation with Patriot/Cobham
have installed ta
"set screw" as described in the e-mail I forwarded
separately. They are
tentatively reporting that it may have solved the
problem.
It wasn't very cold at GGAO over Saturday night. It got
down to about
20C in the Washington area. I have admit I don't
understand the
mechanical issues involved, but if the model if
differential contracting
is accurate, one might wonder how much worse it might
get during the
winter and whether a set screw is sufficient to deal
with this or
whether is a different problem. It would be interesting
to hear
Patriot's take on this.
Cheers, Ed