[Evla-eng] Re: [evlatests] EVLA Cable Wraps

[Barry Clark]

Bob Broilo wrote:

> Since the EVLA software knows which arm the antenna is on, it could
> apply this simple offset and improve the situation for servo,
> astronomers, and operations.
> 
> Please consider this simple software change,
> -Bob.


If I may recall a bit of ancient history, the VLA was originally organized
this way; it seemed as logical to me then as it does to you now.  Turns
out it drove the observers crazy.  Problem is that different arms may move
in opposite directions in azimuth, resulting in an appearance of more net 
move time, since you don't get full data rate until the slowest arm gets on
source.  Perhaps as important, it made it intolerably confusing for the 
astronomer to plan his observation in detail.  The current system was 
implemented in the early eighties, and regarded as a vast improvement.  It 
could be implemented with a different mix of hardware and software if we
need to, but the central feature - that the highest level software regards 
all antennas as having the same azimuth limits, in true azimuth, needs to be
preserved.

If the hardware problems are too difficult, we might consider reducing the
azimuth range.  There is nothing magic about 540 degrees, it is just nice.
A moderate overlap is imperative to keep from having to unwrap too often, 
but we could shave a bit.

I did not understand your remark about needing to move the 'flipper' when the
antenna changes arms.  This sounds like you are applying the 'flipper' 
after the subtraction of the arm offset.  Doesn't it make more sense to 
apply it before?