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Spectral units of the correlator

The correlator has 8 independent units, which can be placed anywhere in the 100-1100MHz band (1GHz 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 x 512 20 SSB
0.078 1 x 512 40 SSB
0.156 2 x 256 80 DSB
0.312 1 x 256 80 SSB
0.625 2 x 128 160 DSB
1.250 1 x 128 160 SSB
2.500 2 x 64 320 DSB
Note that 5% of the passband is lost at both ends 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 1100MHz. The correspondence to the sky frequency depends on the parts of the 4GHz bandwidth which have been selected as correlator inputs.


next up previous
Next: ASTRO Up: Correlator Previous: IF processor
Jan Martin Winters 2007-07-12