[mmaimcal] Data rates and dump times

[Brian Glendenning]

Hi -

Unfortunately it looks like I'll be getting our car repaired in ABQ next
meeting, and on vacation (yay!) the week after that.

As far as I know the most relevant references to previous work are:

MMA Memo #164 (Scott et. al.) ; and
MMA MEMO #192 (Rupen)

The most relevant part of memo #164 is enclosed. I won't attempt to
summarize #192 other than to say that Rupen notes that ultimately we will
want to do OTF interferometry which makes the data rates very high!

Note that the minimum dump time and data rate are both interesting numbers.
For example, we know that the correlator can dump at ~16ms (cross-spectra,
1ms auto), however we have no idea whether the rest of the electronics can
keep up since there is no global spec in the project for this number.

Cheers,
Brian
------------------------------------------------------------------

>From Memo #164

At the Tucson meeting in Oct, `96 the science groups presented their
requirements which are now summarized.

Solar flares and flare stars require temporal resolution of 50-100 msec but
with a reduced number of channels.

Single dish spectral line on-the-fly mapping requires sample rates of 100
Hz.

On-the-fly interferometric mosaicing at sample rates of 1 sec but restricted
to a few thousand channels.

Fast switching (~10 sec cycle) between source and phase calibrator will be
required if a realtime phase correction for atmospheric water vapor is not
possible. The system should support integration times of 10 seconds for the
full correlator output (the phase calibrator will be wideband only). If
shorter cycles are required then multiple cycles can be integrated together
to form one recorded integration.

Assuming the data are stored using scaled integers so that each number takes
2 bytes, all of the above requirements can be met with a maximum data rate
of 10MBytes/second. If all 780 baselines (or 40 telescopes in the single
dish case) are used then the following table holds:

					Min intgn	nchan	Data Rate
Solar flares & Flare stars	70msec	224	10MB/sec
Single dish OTF mapping		3msec		420	10MB/sec
OTF mosaicing 			1sec 		3200	10MB/sec
Fast phase calibration 		10sec 	32000	10MB/sec