[asac] Correlator Modes, for Board Charges

[Al Wootten]

Folks,

We discussed prioritization of correlator modes at the ASAC/NA f2f meeting.
The plans for the ATF and OSF now include the newly installed 2-antenna
correlator, a one baseline copy of the final correlator, instead of the
prototype correlator, which is now deprecated.  The 2-antenna correlator,
with tunable filter banks, supports more modes.  Hence the interpretation of
the charge from the Board is that the ASAC work on prioritization of the
correlator modes.  Remember that all 71 modes are listed in ALMA Memo 556.
Our CSV plan calls for implementing modes which we can exercise on the 
2 antenna correlator at the high site for Early Science.  So please consider 
the questions:

* Are some of the modes more desirable than others?

* Are some modes not available on the 2 antenna correlator so important that
they should be implemented for Early Science on the AOS correlators (this
had better be a VERY strong case!!)?
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Details

What modes are available?  2-antenna correlator has modes 1-18 and 70.
My presentation to the ASAC/NA is available at the agenda for that f2f meeting:
https://wikio.nrao.edu/bin/view/ALMA/17Aug07Agenda
as attachments at the bottom.

A chat with Jim Pisano revealed to me that the correlator modes implemented 
by him on the prototype correlator were not those the Sci IPT recommended Aug 
2005 (apparently he never got our recs; I should have sent them directly to 
him).  But that correlator is now best used as a toaster anyway.  He said:

"The 2-ant correlator can do the following modes:
2 GHz, 1 GHz, 500, 250, 125, 62.5 MHz 'TFB' (modes 1-18)
2GHz 256 channels 'TDM' (mode 70)
single,  dual, & full polarization
2 baseband pairs
2 x 2 Bit correlations only
Each TFB mode can support up to 8192 channels in single pol'n mode

"The prototype correlator capabilities included:
2 GHz (256 channels), 125 MHz (4096 channels), 31.25 MHz (8192 channels)
single,  dual, & full polarization
4 baseband pairs
The prototype correlator is capable of more modes bandwidths, but they are 
untested."

After discussion with Jim Hesser and Ewine I interpret the ASAC charge as:
Which of these myriad modes (2-ant correlator) should have highest priority. 
My recommendation will be the ones in the Commissioning manual which overlap 
the ones that the 2-ant correlator provides.  That is, modes 7,12,13, 18 and 
70.  I think that in the ALMA Memo 556 table, the time-division mode spectral 
resolutions mean MHz though the column is given in kHz.

I did a quick run through of the DRSP; I think this covers the resolutions 
most projects need whether galactic high or low resolution at low frequency 
or extragalactic resolution at high or low frequency. I used a few examples 
for the ASAC/NA and ANASAC presentations.  That will leave the ASAC 14 
additional modes to rank in priority if they wish.  The CSV plan can then be 
updated to discuss the current correlator plan and ASAC recommendations.

Clear skies,
Al
Al Wootten
Interim Project Scientist
ALMA, 40 El Golf, Piso 18
Las Condes, Santiago, Chile
Tel: (56) (2) 467-6128  FAX: (56) (2) 467-6103
Al Wootten Cell +14342424713