Keywords: mrtcal-prog-manual

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## Slow and Fast traces

The IMBFITS files provide 2 antenna streams and associated tables: The slow (1 Hz) and the fast (128 Hz) traces. For each of those traces, some antenna position parameters are available, plus the associated time as MJD values.

As of today (IMBFITS version 2), the 2 traces are in the same FITS extension. Both have the same number of rows, but the fast trace has 128 values per column and per row, while the slow trace has 1 value per column and per row. However, even if they have the same number of rows, they are INDEPENDENT: For example, their MJDs are misaligned by a 2 seconds shift (2 rows). They should not be correlated! In the IMBFITS version 3, the 2 traces will be clearly separated in 2 FITS extensions, which will avoid any misinterpretation.

Note that the caveat exposed above explains why MRTCAL selects more dumps than MIRA in on-the-fly maps: MIRA looks at the antenna slow column `TRACEFLAG` to flag out MJD values in the antenna fast. Because of the 2 seconds shift between the 2 traces, more time dumps are discarded.

Next: Offsets of multi-pixel receiver Up: Antenna offsets Previous: Wobbler switching Contents