[gbtnews] GBT LO1A tolerance not set by config_tool

[koneil at nrao.edu]

To all GBT users,

The tolerance for the LO1A on the GBT is not currently being set by the 
config_tool or ASTRID. As a result any observations which rely on doppler 
updates may have been compromised by this. This will not affect anyone who uses 
the topocentric velocity frame (e.g. pulsar observers). A plan is in place to 
remedy this problem, which will take effect by mid-January, 2006. Note that the 
default tolerance for the LO1 is currently 10Hz. After mid-January this default 
will be changed to 10 Hz or 1/100 the channel spacing, which ever is least.

Until the change takes place, please do the following:

     * If you will be observing between now and mid-January, please add the 
following line to your astrid script to insure you are not affected by an 
incorrect LO1 tolerance (this will set the LO1 tolerance to 10 Hz) : 
SetValues("LO1", {"tolerance": 10})

     * If you have data which was taken on the GBT and wish to know if it was 
compromised, please do the following:
           o Look at the list at http://wiki.gb.nrao.edu/bin/view/Observing/Lo1Problem 
to see if your project is listed. If your project is not listed, the LO1A tolerance
was set to <= 10 Hz (the current default setting) and your project was not compromised.
           o If your project is on the list, you need to decide if an error in 
the channel frequencies equal to (but never greater than) the error listed by 
your project name is a problem. If the channel frequency error listed is greater 
than 1/100 of your final (smoothed) frequency resolution you may have a problem.
           o If your data may be compromised, take a look at the list given at
http://wiki.gb.nrao.edu/bin/view/Observing/LO1ProblemAll to see which observing 
sessions were affected. The "observing session" was defined during your 
observations. It is the same as the directory name for your data.
           o If you still believe you have a problem with your data, contact your 
project support person for help.

We apologize for any problems this may cause our observers.

The GBT staff