For spectral-line observing, the original post-upgrade ``interim'' correlation spectrometer provides four independent sub-correlators, each having eight chips with 1024 lags per chip. Each sub-correlator can be set up with its own independent bandwidth and configuration. Table 4 specifies the available configurations. The maximum bandwidth per sub-correlator is 50 MHz, with 8 other alternative bandwidths being available in decreasing octave steps. Popular configurations combine chips in groups of four to provide 9-level sampling (96% efficiency), interleaved operation (50-MHz bandwidth) or auto+cross correlation (i.e. all four Stokes parameters).

Config | Max Bw | Pol/Sbc | Boards | Lags/Sbc & Resn - |

per Sbc (MHz) | Used | (kms `@` 1420 MHz) |
||

9-level | 25 | 1 | 4 | 2048 (2.6) |

9-level | 25 | 2 | 4 | 1024 (5.2) |

3-level | 25 | 2 | 4 | 2048 (2.6) |

3-level interleaved | 50 | 1 | 4 | 4096 (2.6) |

3-level interleaved | 50 | 2 | 4 | 2048 (5.2) |

3-level Stokes | 25 | Full Stokes | 4 | 2048 (2.6) |

Notes:

1) The spectrometer has its available bandwidths defined by the following filters: a) Analog filter - 50 MHz, b) Digital filters - 25, 12.5, 6.25, 3.125, 1.563, 0.781, 0.391, 0.195 MHz

2) Double Nyquist sampling can be used with all configurations except interleaved, but decreases the maximum bandwidth by a factor of two.

3) 3-level, double Nyquist, 12.5-MHz bw and below will give 4 sub-bands with better resolution than the corresponding 9-level configuration.

4) 9-level operation achieves 96% of the signal-to-noise of analog correlation, whereas 3-level achieves 81%.

5) Different correlator boards can operate with different configurations to each other.

6) The fastest dump rate for spectral-line usage is about 10 Hz.

7) The number of lags used can be reduced by a factor of 2 down to 16 lags. The size of the output file will be proportional to the number of lags.

Robert Minchin 2017-10-30