[mmaimcal] forwarded message from Ray Escoffier

[Mark Holdaway]

When we were looking into the test array site, we considerred Kit Peak,
near the 12M.  We could get something like 500m baselines, which Frazer
Owen argued was NOT long enough.  (Peter said "Don't you want to have 3km
baselines so you can test what the MMA will really have?") Based on that
argument, plus more weight from "ease of site use" and "superior
infrastructure"  arguments, the test array was sent to the VLA Site. 

That being said, I would argue that if fast switching works on a 100m
baseline, it works pretty much as well on a 1000m or 10000m baseline.
100m is actually a bit too short as it is close to the effective
switching baseline (ie, it is 10s worth of atmospheric crossing).
Also, with just 2 antennas, you will need higher SNR on the visibilities
than if you had 40...so, either brighter cal sources or longer time
(probably both) for fast switching tests...which pushes us to longer
baselines.   I would say that we want 500 - 1000m for a long baseline.

We can make similar arguments based on radiometric phase calibration
techniques, but we probably end up at between 100m and 500m.


However, we also want to do a lot of tests with very short baselines:
	* mosaicing short baseline recovery
	* verify antennas can get that close without problems
	* "zero baseline" stability tests to measure the
		electronic and antenna phase stability
	* science

So, we need:
	* multiple antennas (ie, 3 or 4) in the test array
or
	* multiple stations and a transporter
or
	* forget some of the tests we had hoped to do


	-Mark