FREQUENCY CONFIGURATIONS

In addition to the visibility data, the online processor stores the the header information for each individual spectral band of data into a file sp_read under the directory of a data file, containing a set of spectral bands which can be either a correlator chunk (spectral window) or the pseudo-continumm channel ( a single channel that is a vector-average from all the channels of the spectral bands). In history (prior to 2009 spring), the SMA frequency configuration consists of one continuum channel (c1) and 24 spectral bands (s1 to s24) with a total bandwidth of 2 GHz for each sideband; this correlation operation mode is often referred as a 2 GHz mode. For a uniform resolution mode, all the 24 spectral chunks have the same channel resolution. For a hybrid spectral resolution mode, some of spectral chunks may be empty. Note that after 2009 spring, this 2 GHz mode has been occasionally used for high spectral resolution observations. The SMA Software Limits have been followed to program the data reduction software used for the old standard.

Since 2009 spring, the IF bands have been doubled. The double-band frequency configuration then consists of one continuum channel (c1) and 48 spectral bands (s1 to s48) with a total bandwidth of 4 GHz for each sideband. This double-band mode is also referred as a 4 GHz mode.

In the near future, the IF bands will be doubled again with a total bandwidth of 8 GHz. In addition to previous 48 spectral bands, SMA will add additional two broad (wide) spectral bands with a total of 28000 channels and 2 GHz bandwidth for each. Thus, the new SMA frequency configuration will consists of one continuum channel (c1), 48 spectral bands (s1 to s48) and two wide bands (w1 and w2). Therefore, each sideband will have a total of 51 spectral bands. New SMA Software Limits have been discussed recently. The new standard will be followed in Miriad programming for SMA data reduction.