At the VLA, a rubidium time standard is used in place of the maser, which
is expensive and sometimes unavailable.  What should ALMA do, Clint asks?
Is the rubidium standard suitable?

I discussed this with Mark Claussen and Ed Fomalont.  Ed thinks that
there are better choices for a time reference available today than a
rubidium standard.  I think that the maser should be used whenever
available but that the backup could be a more current solution than the
rubidium standard.  There may be another maser at the APEX or ASTE sites.  
If we can't afford two hydrogen masers, we should identify and cost the 
alternatives to the rubidium standard and consider using those if possible.

 What could be economically 
subsituted for a rubidium standard when backing up the maser.  Rubidum 
is used as a back up at the VLA because they are cheap, in fact, Leon 
Abeyta tells me they were "free."  We've always gone with rubidium 
because we've obtained them free. According to Leon, a cesium is the 
next most expensive standard, but since you can't do VLBI with it, it's 
no better than a rubidium.  Leon does report that "we back up the 
rubidium with an 'extremely low noise' crystal that I am told is good 
enough to run the entire VLA."; is that it?  Maybe a discplined GPS?

Thoughts?