Spectral units of the correlator

The correlator has 8 independent units, which can be placed anywhere in the 100-1100 MHz band (1 GHz bandwidth). 7 different modes of configuration are available, characterized in the following by couples of total bandwidth/number of channels. In the 3 DSB modes (320MHz/128, 160MHz/256, 80MHz/512 - see Table) the two central channels may be perturbed by the Gibbs phenomenon if the observed source has a strong continuum. When using these modes, it is recommended to avoid centering the most important part of the lines in the middle of the band of the correlator unit. In the remaining SSB modes (160MHz/128, 80MHz/256, 40MHz/512, 20MHz/512) the two central channels are not affected by the Gibbs phenomenon and, therefore, these modes may be preferable for some spectroscopic studies.

Spacing	Channels	Bandwidth	Mode
(MHz)		(MHz)
0.039	$1 \times 512$	20	SSB
0.078	$1 \times 512$	40	SSB
0.156	$2 \times 256$	80	DSB
0.312	$1 \times 256$	80	SSB
0.625	$2 \times 128$	160	DSB
1.250	$1 \times 128$	160	SSB
2.500	$2 \times 64$	320	DSB

Note that 5% of the passband is lost at the end of each subband. The 8 units can be independently connected to the first or the second correlator entry, as selected by the IF processor (see above). Please note that the center frequency is expressed - as in the old system - in the frequency range seen by the correlator, i.e. 100 to 1100 MHz. The correspondence to the sky frequency depends on the parts of the 4 GHz bandwidth which have been selected as correlator inputs.