====== Autocorrelation spectra plots ======

At the end of every scan, the ''postob'' procedure will run a script to extract some Mark5 data and display the autocorrelations of the 16 channels. Good data should contain quite flat bandpasses and zero phase. For example:

{{:operations:gv_dd1.pos-1.png?500|}}

If the spectra look like this, then everything is OK, dismiss the ''gv'' window. The DBBC will sometimes drop channels, resulting in zero amplitude autocorrelations, or may show strange spectra with a step in the middle, like this:

{{:operations:gv_dd1.pos-3.png?500|}}

In these cases, it is necessary to reprogram the DBBC. Instructions are here
  * [[hardware:dbbc.reprogram|Reprogramming the DBBC]]
**Please make a note in the log when you reprogram the DBBC**. Note that previous spectra plots are kept on pcfshb in ''/home/oper/auto_cor_test'' so it's possible to view these and see when problems occurred. To view these files, use ''gv'', e.g.<code>gv 2010_11_22_024630.epi</code>

For an AUST experiment the filters make the channel spectra look like this example from hb 12m:

{{:operations:aust_hb.png|}}

Sometimes, a spectrum will look like this:

{{:operations:gv_dd1.pos-2.png?500|}}

This appears to be a bug in the extraction/plotting software (it happens when the software extracts no data) and can be safely ignored. Wait for the end of the next scan to see the next plot.