VLA Correlator Page

VLA Correlator Page

This page controls the correlator and data collection process. The correlator mode and integration time can be set for all observations. For spectral line data it is also possible to specify filtering done in the Array Processor and select some of the spectral channels.

Correlator Mode

The items in the Choice are relatively self-explanatory:

Continuum
Single IF spectrum, correlation AA
Single IF spectrum, correlation BB
Single IF spectrum, correlation CC
Single IF spectrum, correlation DD
Dual IF spectrum, correlation AA, BB
Dual IF spectrum, correlation AA, CC
Dual IF spectrum, correlation AA, DD
Dual IF spectrum, correlation BB, CC
Dual IF spectrum, correlation BB, DD
Dual IF spectrum, correlation CC, DD
Four IF spectra, correlations AA, BB, CC, DD
Two IF, polarization spectra, correlation AA, AC, CA, CC
Two IF, polarization spectra, correlation BB, BD, DB, DD

where "A", "B", "C", and "D" refer to the IFs involved in the correlation.

Integration Time

This is the integration time in seconds. Allowed values are:

0 ( 10 sec)
1 ( 1 2/3 sec)
2 ( 3 1/3 sec)
3 ( 3 1/3 sec)
4 ( 5 sec)
5 ( 5 sec)
6 ( 6 2/3 sec)
7 (8 1/3 sec)
8 (8 1/3 sec)
9 (10 sec)
10
multiples of 10

Array Processor mode (Spectral Line Only)

The Array Processor Options. If the Correlator Mode is Continuum or blank, these fields are not applicable; OBSERVE will not allow you to set or modify it. Up to three options may be selected together. If all options are blank, they are written to the OBSERVE file as such. The VLA on-line system will interpret blanks as standard observing with no special options. The options are:

blank
bandpass normalize
hanning smoothing
sum of baselines
lag spectrum

Lag Spectrum is mutually exclusive from all other options.

Channel Count (Spectral Line Only)

Specifies the Number of Channels to use on all baselines. If the Correlator Mode is Continuum or blank, this field is not applicable; OBSERVE will not allow you to set or modify it. The number of channels selected here is a power of 2, which is less than or equal to the maximum number of channels (this is indicated by the option selected under Bandwidth). Select "all" to record the maximum number of channels for your observing mode.

Before choosing a value here, it is essential to have selected first the correct Correlator Mode and the correct Array Processor Option (in particular Hanning Smoothing if desired), and then subsequently the Bandwidth (on the LO or Source Page). The Number of Channels is currently constrained in the on-line system to be the same for all IFs.

Starting Channel (Spectral Line Only)

Specifies the Starting Channel for all baselines. If the Correlator Mode is Continuum or blank, this field is not applicable; OBSERVE will not allow you to set or modify it. In order that valid data appears in all of the selected channels, the Starting Channel selected here is an integer (n) which must be 0 <= n < max, where max = maxchannels - number of channels and maxchannels is the maximum number of channels, which is indicated by the option selected under Bandwidth, and number of channels is as set on this Page as Channel Count.

If left blank, it is written to the OBSERVE file as such. The VLA on-line system will interpret a blank as 0 (zero). The Starting Channel is currently constrained in the VLA on-line system to be the same for all IFs.