3.5 Frequency Catalog

SCHED is able to fill in many items in setup files based on knowledge of possible frequency setups at the stations as described in the frequency catalog. This allows the user to only specify basic information. A reasonable minimum set is: NCHAN, BBFILTER, BITS, POL (can be DUAL), and either FREQREF (and FREQOFF) or BAND. The frequency catalog also allows SCHED to check user specified values against standard sets to warn of any oddities.

Most users will not touch the frequency catalog. If they need a setup that does not conform to what is in the catalog, they should just make the necessary setup files and ignore the warnings after making sure that the special files are correct. Be very careful doing this. There are filters on many of the LO and IF cables, at least on the VLBA, that most users probably are not aware of. Any special setup files that do not match one of the standards should be shown to Craig Walker for approval. If it is a good one, it may be added to the standards. However, the standard set is essentially complete for the VLBA. If SCHED complains about yours, it is likely to be in error. If a user really wants his/her own frequency catalog, use the input parameter FREQFILE to specify the file name.

There is a lot of information about available frequencies, receivers, frequency ranges, filters etc, especially at the VLBA, in the standard frequency catalog. A table of information about possible setups for observations within a frequency range can be made by running SCHED with FREQLIST = lowfreq, highfreq (eg freqlist=4800,8900) as the only input. The frequencies are in MHz. If only one frequency is given, the second will be set equal to the first. SCHED will produce a table in file frequencies.list containing details of the information available on how to set up these frequencies at all known sites. SCHED will then quit. Note that it is not necessary to transfer this information to your setup files — SCHED will do that automatically based on your frequency and polarization requests in the setup file. To examine the catalog itself, look at $SCHED/catalogs/freq.dat or, if reading the html version of the manual, click here..

3.5.1 List of Frequency File Parameters

The parameters of the frequency file tell SCHED over what frequency range the group if usable and on which stations. Most of the parameters are the same as parameters in the setup file since they are meant for direct substitution once the correct frequency group has been identified. There is no defaulting between groups of inputs — all parameters are reset to zero, blank, or some equivalent value.

For the VLA, IF’s A and C will be assumed to apply to VLA27 while IF’s B and D will be assumed to apply to VLA1. All standard frequency groups will have both VLA IF’s on the same frequency. Anything more complicated requires a setup file from the user.

Up to 10 stations with this setup. This will be matched against the station name in the setup file. The name VLBA will be a default for all VLBA stations.
A ranking with low values prefered. This allows preference of one setup over another if both match the required frequencies. For example, the narrow band 50 cm receiver would be chosen over the wide band one for narrow band observations despite the fact that both would match the requested frequencies.
A name for the frequency group. It is used in listing and error notes to help the user find the right one. Up to 12 characters long. Any string ok.
A comment about the setup that will go to various listings. It is wise to note any limitations here that might not be obvious to a user. Up to 80 characters.
The name of the IF for up to 8 IF descriptions (eg. A, B, C, D). There are a larger number than there are phsical IFs to allow description of such systems as the VLBA 50/90 cm system where there are more than one signal in each IF.

For antennas in the EVN that have VLBA(4) DARs, the codes in use are usually A and C (LCP and RCP). For MkIV antennas there are two IF distributors that can one can choose to connect to either IF channel. Each distributor is connected to a fixed subset of the BBC’s, either the odds or the evens. The normal situation has IF 1N on LCP and 2N on RCP, but alternate channels 1A or 2A can be connected if more than the first 7 BBC’s need to be set to a single polarization.

For the DBBC, IFNAME contains two characters. The first (A-D) gives the conditioning module to be used, the second (1-4) determines which of the switchable inputs on that conditioning module is to be selected. The signal available on each input depends on the local station wiring, so careful catalogue maintenance is required.

An alternate IF name for this frequency setup. For the Mark IV systems, the odd BBC’s are attached to IF’s 1N and 1A. The even BBC’s are attached to 2N and 2A. Generally the same signal is put on 1N and 2A while another (other polarization) is put on 2N and 1A. When assigning IF names using frequency table information, sched will pick IFNAME or ALTIFN depending on whether the BBC is even or odd and on the first digit of the names.
The low edge of the RF frequency range covered by each IF. SCHED will try to find the group with all the channels best centered in the IF. However, some channels will allowed to be outside the range if necessary, as is common on the VLA.
The high edge of the RF frequency range covered by each IF.

For Mark IV systems, the frequency ranges in the frequency catalog are calculated with the constraint that the complete range can be obtained with the station preferred patching, i.e. with consistently using high or low output on the IF distributor. More frequency coverage can be obtained with detailed knowledge and requires a manual setup.

The lowest RF frequency for channel 1. If non-zero, channel 1 will be required to fall in the range specified by CH1RF1 and CH1RF2. This is mainly to be sure that the right filter is used at 2cm on the VLBA.
The highest frequency for channel 1. See CH1RF1
The FIRSTLO for each IF channel.
The FE (receiver specification) for each channel. Use omit for unused channels.
The polarization of the channel (RCP or LCP).
The SYNTH setting for each of the three front end synthesizers on the VLBA.
Use the wideband scheme at 4 cm on the VLBA. See the setup parameter DUALX.
Setting for the 50 cm filter. See setup file parameter LCP50CM
Setting for the 50 cm filter. See setup file parameter RCP50CM
Only use this IF if CHNSTA matches the station name. This allows the same groups to be used for VLA1 and VLA27, but to differ in the IFNAME. Options are the station name or BOTH. This facility has been disabled and may be removed. It has been made obsolete by the new digital patch panel at the VLA and the effort by SCHED to determine which IF’s are to be used for the each setup depending on the specified modes in the schedule. Modes VA, VR and VL require different IF restrictions.

The following are OBSOLETE VLA parameters that should not be used.

The VLA frequency band. See setup file parameter VLABAND
The VLA bandwidth codes.
The VLA first LO.
The other VLA first LO.
The VLA gain file name.
The VLA ROT file name.
The VLA AC F6 setting.
The VLA BD F6 setting.
The VLA BD F6 setting.