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Backend characteristics

The versatility of the IF distribution box allows a large flexibility in the use of the 30-m telescope backends (splittable 100 kHz and 1 MHz filterbanks, autocorrelators, AOS). This allows an optimum frequency resolution for most programmes.

Normally, the filter banks add very little noise to the receivers. The filters have rectangular shapes with widths very close to 1 MHz. Their spacing is also close to 1 MHz.

In the case of the autocorrelators, a number of bandwidths (20-520 MHz) and channel resolutions (from 10 kHz up) can be achieved. It should be noted however that the bandwidths larger than 80 MHz are made up of several subbands the baselines of which can be slightly offset from one another after a long integration (mostly when position switching against a continuum source). It is often advisable to make the observations with different centering of the autocorrelators to monitor these effects. The autocorrelators samplers have 2 bits. The limited number of sampling levels results in an increase of the recorded noise by = 15%.

For the AOS, the resolution bandwidth is 1.1 MHz, and the noise bandwidth about 1.7 MHz.

Robert Lucas
Thu Mar 9 12:14:01 MET 1995