Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/people/Tasso.Tzioumis/sched/Standard_Setup_Files.html
Дата изменения: Unknown
Дата индексирования: Sun Apr 10 11:20:52 2016
Кодировка:
Поисковые слова: о п п

Standard Setup Files

Over 200 standard setup files have been created, covering many of the normal modes of observing. They are available at the same place as the code for SCHED in a ``setups'' subdirectory. Users may opt to use these standard setups. However, now that BAND is available, it will make more sense for most users to make their own setups, imbedded in the SCHED input file. See the example egvlba.key for a template. The only parameters required in such a setup are BAND, NCHAN, BBFILTER, BITS, and POL. You need to know all of those just to pick the standard setup file to use so why not make your own? In fact, as users get accustomed to doing this, many of the standard setups may be dropped. This file has not been updated from MARK5A to MARK5C.

There are cases, however, when use of the standard files is recommended. These especially include precisely defined, and somewhat complex cases like the Mark III standard modes (although MarkIII went the way of the dinosaur long ago. Also, if none of the standard files matches the exact needs of a project, there is likely to be one that is close and can be modified as required. This is generally safer than creating a setup file from scratch because it will be clear what parameters are required.

The standard setup files take advantage of the defaulting ability of SCHED. If you are interested in what most of the setup parameters will actually be set to, the best way to do this is to run a simple dummy schedule that uses the setup and look at the details reported in the summary file. A simple file like the simple example given earlier should do (with OBSTYPE set to VLBI), although cover and correlator information will be required.

Standard setup files are named according to the following conventions:

``v'' files:

These are setup files for VLBI observations using VLBA recording formats. The VLBA system is very flexible so there are large numbers of options. There is much more information in the name which might be best described with an example. The file v6cm-128-4-2-L.set is for 6 cm observations in VLBA format. The first number after a ``-'' gives the total bit rate in Mbits/s which is 128 in this case. The next number is the number of channels (4). The last number is the number of bits per sample (2). If the file only uses one polarization, there will be an ``L'' or an ``R'' at the end. If the file uses upper and lower sidebands where all upper sidebands could be used on the VLBA, there will be a ``UL'' appended. These files can be used when observing with sites such as Effelsberg which have a limited number of BBCs. All setup files, by convention, end in ``.set''. Note that one can deduce the bandwidth and sample rate from the above information assuming Nyquist sampling. With 128 Mbits/s and 4 channels, the channel bit rate must be 32 Mbits/s. With 2 bits per channel, this means that the sample rate is 16 Msamples/s. Nyquist sampling implies 8 MHz bandwidth per channel, which, with 4 channels, gives 32 MHz overall bandwidth.

``m3'' files:

These are setup files for Mark III observations. SCHED only supports Mark III observing for systems with VLBA control computers and data aquisition systems. These include the VLBA, the VLA, Green Bank, and, optionally, Effelsberg. An example file would be m3e18cmd.set. This means Mark III, mode E (4 passes per head position), 18 cm observing wavelength, double speed. Here, double speed means recording at 8 Mbits/s per track. With Mark III, there is a one-to-one correspondence between tracks and channels and there are a total of 28 possible tracks. Also, all sampling is in one bit mode. Mode E uses 7 tracks (channels) at a time so this setup specifies a total bit rate of (7 * 8) = 56 Mbits/s and, with Nyquist sampling, 28 MHz total bandwidth.

``vla'' files:

These are setup files for VLA-only observations. The don't specify any tape related information.

``pt'' files:

These are setup files for VLBA pointing and antenna temperature measurements.

``pc'' files:

These are setup files for VLBA pulse cal tests.

``nug'' files:

These are setup files for Mark II observations. The standard ``nug'' files are not being maintained any more and may will not have the stations in them that are doing Mark II. They will need to be modified if anyone uses them. If they are, please send examples to cwalker@nrao.edu so new standards can be established. Mark II is no longer available on most antennas, including all that are operated by NRAO.