Starting Proposal Cycle 2014A (deadline August 1, 2013) TUNE should no longer be used. Much of TUNE's functionality is now part of the OPT
"TUNE" - a tool for VLA spectral line setup
"TUNE" is a tool designed to help users find the optimum correlator setup for simultaneous observation of multiple lines with the VLA, visualize how spectral windows will be placed within the available correlator basebands and where the spectral lines are located within a spectral window. From line frequencies and subband bandwidths as inputs, TUNE can recommend a baseband center frequency and subband offsets from this center frequency.
TUNE is python-based and available either as a stand-alone python code or as a web-based utility. If you plan to submit a proposal to observe multiple lines within a single VLA baseband, we suggest that you use TUNE to check the feasibility of your proposed observations and include a note in your technical justification indicating that you have used TUNE to verify the setup.
Before using TUNE, please review the Spectral Line Observing Guide which provides baseband tuning restrictions, describes correlator capabilities offered, and discusses issues relevant to planning spectral line observations. In summary,
The actual number of available subbands will depend on the resolution and bandwidth chosen (higher resolution will use up more correlator hardware resources, limiting the total number of subbands that can be used). For more information on the 3/8 bit sampler, and the current correlator capabilities, see the online documentation here.
Each baseband is comprised of a series of 8 or 16 "blocks" that are 128 MHz wide. An individual subband must fall entirely within one of these blocks, as subbands cannot cross the boundary between these blocks, known as a "128MHz suckout". We recommend that subband edges be at least a few MHz away from these 128 MHz suckouts to avoid regions of sensitivity falloff. Additionally, one should try to avoid placing line(s) too close to the subband edges where again, decreased sensitivity may become an issue. TUNE can help to find a baseband setup that avoids placing subbands close to the 128 MHz suckouts and avoids placing line(s) close to the subband edges.
After determining the target spectral lines and subband widths, use TUNE to find baseband center frequency and subband offsets. TUNE can be run for a single baseband at a time. So, if observing all target lines requires multiple basebands, you must run TUNE for each baseband separately. The , which can be downloaded and run locally from the command line, requires that python and matplotlib are pre-installed. The stand-alone tool was tested on Python 2.4.3 and matplotlib 1.0.1 on Red Hat Enterprise Linux. If you have compatibility issues with other versions of Python and matplotlib, please contact the NRAO helpdesk. The offers ease of use, with inputs entered through an online form, but provides slightly lower flexibility than the stand-alone tool. A description of the required inputs, generated outputs, and examples of the command line input syntax follow.
NOTE: Depending on the spectral resolution requirements for your
science, finite correlator resources may limit the available total
number of subbands and/or polarization products. Once again, consult the
Spectral Line Observing Guide.
Another tool, called GOST (General Observing Setup Tool) can calculate the
correlator resource budget given the lines and spectral resolutions desired.
If you are at all in doubt, please check your line/subband selections using
to make sure that you can observe all desired lines with adequate spectral
resolution while using the set up suggested by TUNE. Otherwise, you may need
to exclude one or more line(s) from your list.
(1) Select the output file style (either "Detailed" or "Summary"), and enter an output file name. TUNE outputs a pdf file that contains (i) images of the baseband positioning within the receiver band, (ii) images showing subband and line positions within the baseband, and (3) a summary of recommended baseband center frequency and subband offsets. The "Detailed" output, which also shows the position of each individual line within its subband, is recommended for the user when inspecting the correlator setup.
(2) Select the correlator mode (i.e. 3- or 8-bit sampling, "flexible tuning" on or off).
(3) Specify the topocentric optical velocity and/or the redshift of the source.
(4) Specify line frequencies and subband bandwidths. If a topocentric source velocity/redshift has already been entered, provide the line rest frequencies here. Alternatively, you may leave the velocity/redshift fields set to 0 and input the expected sky frequencies of the lines here. To convert rest frequency to appropriate sky frequency, you may use the Online Dopset Tool.
(5) Run TUNE and inspect the output. See here for an example of a typical output file from TUNE.
Note: TUNE output should be taken as a guideline rather than the
final/best possible/optimum configuration for each case. Depending on your
specific requirements, "the best" set up is subjective, and may be different
from the setup recommended by TUNE.
Command line input syntax for the stand-alone tool:
Inputs are passed into the stand-alone tool through argument flags with the
following syntax (the order of input options is not important):
will run TUNE specifying: the 8-bit samplers; no flexible tuning (so all subbands have the same resolution and bandwidth); 4 lines at frequencies of 23.694, 23.723, 23.870 and 24.139 GHz; 4 MHz subband bandwidths; and lines are at a red shift of 0.1
uses the 8-bit sampler without flexible tuning, at a redshift of 0.1 and uses the -i flag to retrieve line frequencies and bandwidths from the input file named tune_input.txt, which is a free format two column ascii file.
The input file (tune_input.txt) equivalent to the line input in Example 1 would contain:
23.694 4.0 23.723 4.0 23.870 4.0 24.139 4.0
Inline help for the stand-alone script is also available by typing
from the terminal (without any extra arguments).