VEX Parameter Tables
Rev 1.5c Nov 16, 2009
Preface to the wiki version This document is a nearly direct translation from the MS Word version of this document to Twiki wiki format. Along the way a very few typos were corrected and typewriter font has been employed to represent literal text. In addition, a few previously agreed, but undocumented, amendments to the VEX standard (such as LBADR) have been added. To this end, the version number has been bumped from Rev 1.5b to Rev 1.5c. This wiki-fied document will serve as the starting point to the definition of Vex 2.0.
Each VEX primitive $block is allowed to specify only parameters which are defined for that type of $block. The VEX Parameter Tables define in detail these parameters for each type of $block. Each table lists the allowed parameter names and the associated fields. Field numbers in parenthesis are optional. Parameter type '&link' is a VEX linkword as defined in the VEX documentation. If 'units' are specified, the field must have a units label of the proper type; 'units' enclosed in parenthesis are assumed and should not be labeled. Not all parameters need to be specified for a given experiment, only those which are 'relevant'. This listing does not attempt to specify the set of 'relevant' parameters, but is instead left to the assumed expertise of the scheduling-software writer. This listing is not to be regarded as necessarily complete, either with regard to $blocks or the set of native parameters within the $blocks. Many $blocks, particularly the
$
xxxx
_OBS
blocks, are not yet specified. These $blocks will be defined in the near future. Additional parameters will undoubtedly be added as the need arises.
$ANTENNA
Block
The
$ANTENNA
block specifies the detailed characteristics of the antenna itself, including the type of mount and pointing characteristics.
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
antenna_diam |
1 |
Antenna diameter |
real |
> 0 |
length |
|
antenna_name |
1 |
Antenna name |
char |
|
|
Useful, if needed, to distinguish particular antenna from site (portable antenna, for example) |
axis_type |
1 |
Primary axis type |
char |
az ¦ ha ¦ x ¦ fixed |
|
Typically, axis_type=az:el; or axis_type=ha:dec; or axis_type=x:yns; (N/S orientation) or axis_type=x:yew; (E/W orientation), etc... |
|
(2) |
Secondary axis type |
char |
el ¦ dec ¦ yns ¦ yew |
|
Pairing of parameters 1 and 2 must make sense (see comment immediately above) |
|
2 |
axis orientation |
char |
|
angle |
0 deg - north/south orientation; 90 deg - east/west orientation |
axis_offset |
2 |
real |
|
length |
|
|
antenna_motion |
1 |
Axis type |
char |
(axis type) |
|
Must be one antenna_motion= statement for each motion axis. |
|
2 |
Slew rate |
real |
|
ang/time |
|
|
3 |
Settling time |
real |
|
time |
|
pointing_sector |
1 |
Sector ID or cable-wrap zone ID |
&link |
|
|
May be used to specify pointing sector in $SCHED block |
|
2 |
Axis type |
char |
(axis type) |
|
|
|
3 |
Lower limit |
real |
|
angle |
Upper limit > Lower limit |
|
4 |
Upper limit |
real |
|
angle |
|
|
(5) |
Axis type |
char |
(axis type) |
|
|
|
(6) |
Lower limit |
real |
|
angle |
Upper limit > Lower limit |
|
(7) |
Upper limit |
real |
|
angle |
|
$BBC
Block
The
$BBC
block connects physical BBC's to the 'logical' BBC's defined in the
$FREQ
section, and also specifies the connection of the BBC to a 'logical' IF.
Notes:
- All logical BBC's defined in the selected
$FREQ
'def' must be present in the selected $BBC
'def', but not necessary vice versa.
- The
$BBC
block is ignored by the correlator.
- In the case of digital back ends, the BBCs are not actually physical, but will be numbered as such. In systems with multiple digital back ends, the BBC numbers begin at 1 for each. Details TBD
$CLOCK
Block
The
$CLOCK
section specifies the necessary clock parameters for proper correlation of the data. Normally, this information will be taken from the station logs, transcribed manually or, as a last resort, determined from a fringe search at the correlator. Obviously, the
$CLOCK
section is needed only by the correlator.
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
|
2 |
'clock_early' - offset of formatter 1-pps tick with respect to UTC |
real |
|
time |
>0 for formatter tick early |
|
(4) |
Clock rate |
real |
|
time/time |
For example, usec/sec |
|
(3) |
Epoch of origin of clock model |
epoch |
|
epoch |
Needed if clock rate or acceleration specified |
clock_early |
(1) |
Starting epoch for validity of this clock model |
epoch |
|
epoch |
Model in this statement assumed valid until next specified epoch, if any. May be null of model is valid for entire experiment. |
Notes:
- In case of 'clock breaks', where multiple sets of clock parameters must be specified for a station during a single experiment, multiple 'clock=' statements may be used, each specifying the starting epoch of validity for the model in the corresponding statement.
$DAS
Block
The
$DAS
block is intended to define the recording hardware present at a station. Because of the many combinations possible, various elements of the hardware are separately specified.
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
record_transport_type |
1 |
Transport type |
char |
Mark3A ¦ Mark4 ¦ VLBA ¦ VLBAG ¦ S2 ¦ K4 ¦ Mark5A |
|
Additional types may be added. 'S2' is also used for LBADR |
|
(2) |
Revision level |
char |
|
|
Example: '1.0' |
electronics_rack_type |
1 |
Type of electronics rack |
char |
Mark3A ¦ Mark4 ¦ VLBA ¦ VLBAG ¦ S2 ¦ K4 ¦ LBA |
|
|
number_drives |
1 |
Number of tape drives (transports) |
int |
|
|
Number of physical drives connected to system |
headstack |
1 |
Headstack# |
int |
1-4 |
|
Specifies correspondence between physical headstack and logical drive. Relevant for MkIIIA, MkIV, VLBA, Mark 5A. |
|
2 |
Headstack function |
char |
read ¦ write ¦ read/write |
|
|
|
3 |
Drive-number offset with which this headstack is associated |
int |
|
|
Added to drive# specified in the station statement in $SCHED block to determine physical drive#. Normally 0 for single-drive systems. |
record_density |
1 |
Longitudinal bit density along track |
int |
|
(bpi) |
Usually 33,333 or 56,000 (bpi unit is assumed). Used to compute tape speed. Relevant only for MkIII, MkIV, VLBA systems. |
tape_length |
1 |
Tape length |
int |
|
length ¦ time |
For Mark IIIA, Mark IV, VLBA: actual tape length. For S2, K4: recording time at data rate specified in field 2. |
|
(2) |
S2 tape speed |
char |
slp ¦ ep |
(Mbps) |
Relevant only for S2 |
|
(3) |
Number of S2 cassettes |
int |
1-8 |
|
Must be consistent with total date rate (each S2 cassette records 16 Mbps) |
recording_system_ID |
1 |
Recording-system serial number |
int |
|
|
Must be unique for each system of a given type within an experiment. This information is often recorded on tape and used at the correlator. See Notes below. |
record_transport_name |
1 |
Recording-transport name |
char |
|
|
Identifies a particular recording transport. Mostly useful for transportable recording systems. |
electronics_rack_ID |
1 |
Electronics rack serial number |
int |
|
|
Identifies particular electronics rack |
electronics_rack_name |
1 |
Electronics rack name |
char |
|
|
Like a serial number, but a name |
tape_motion |
1 |
Specifies how tape is to be controlled |
char |
start&stop ¦ continuous ¦ adaptive |
|
|
|
2 |
Tape early-start time |
int |
>=0 |
time |
Relevant for start&stop and adaptive motion; specifies how soon tape should start before expected good data. |
|
(3) |
Late stop time |
int |
|
time |
Relevant for S2 only. Specifies length of time tape should continue running after end of valid data. Typically 0.5 minutes. |
|
(4) |
Minimum gap for stopping tape |
int |
|
time |
Relevant for S2 only. Specifies minimum valid-data time gap during which tape will be stopped. Typically 3 minutes. |
tape_control |
1 |
Define master station in cluster |
char |
master |
|
Relevant only in antenna cluster where data from more than one station is recorded on a single recording system. Defines which antenna controls tape motion. Others are assumed to be slaves. |
Notes:
- The DAS parameters are intended to be sufficient to describe any of the many variants of Mark3A, Mark4, Mark5 and VLBA systems currently deployed. Additional parameters may have to be added in the future as systems evolve.
- For Mark IIIA, Mark IV, VLBA and Mark 5A systems, the
headstack
statement indicates which 'headstack outputs' from the formatter are connected to the recording system(s). There must be one headstack
statement for each formatter 'headstack output' to be recorded. Multiple recording systems may be connected to a single formatter.
- If multiple headstacks on same drive, each headstack must have a different headstack# (e.g. Mark IV). Systems with multiple simultaneously-recording headstacks on 2 drives (e.g. VLBA with 2 drives) must have two 'headstack=' statements with a different headstack# and logical drive linkword. The headstack #'s must correspond to the headstack #'s in the
$TRACKS
block.
- The
recording_system_ID
statement identifies the particular DAS used, akin to a serial number, which is usually written in the aux-data field of the recorded data. The recording_system_ID of each DAS within a given type (e.g., Mark4, VLBA, K4, etc) must be different for each DAS within an experiment; the recording_system_ID of a particular DAS is usually assigned at the time of manufacture. The recording_system_ID
can be used by the correlator to positively identify the particular DAS upon which a tape was written. The parameter electronics_rack_ID
is similar.
- If two or more antennas share the same DAS, the
$STATION
'defs' for the corresponding antennas must have 'refs' to exactly the same set of $DAS
keywords, including particularly the recording_system_ID
parameter, except that one (and only one) of the stations must declare itself as the tape-control master with the inclusion of a tape_control=master;
statement within the referenced $DAS
'defs' for that station.
$EOP
Block
The
$EOP
block specifies the earth-orientation parameter to be used by the correlator; not needed for scheduling or data-taking.
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
TAI-UTC |
1 |
Ephemeris TAI-UTC |
real |
|
time |
Normally fixed for entire experiment |
A1-TAI |
1 |
Ephemeris A1-TAI |
real |
|
time |
Normally fixed for entire experiment |
eop_ref_epoch |
1 |
Epoch of first 'EOP point' |
epoch |
|
epoch |
|
num_eop_points |
1 |
Number EOP points |
int |
|
|
Number of points over which interpolation is done |
eop_interval |
1 |
Time space of EOP points |
real |
|
time |
Typically 24 hrs |
ut1-utc |
1 - num_eop_points |
Time series of ut1-utc values |
real |
|
time |
Must be num_eop_points values in this statement. Units specification may be omitted after first field. |
x_wobble |
1 - num_eop_points |
Time series of x-pole values |
real |
|
angle |
Must be num_eop_points values in this statement. Units specification may be omitted after first field. |
y_wobble |
1 - num_eop_points |
Time series of y-pole values |
real |
|
angle |
Must be num_eop_points values in this statement. Units specification may be omitted after first field. |
$EXPER
Block
The
$EXPER
block contains general information useful for the success of the VLBI administrative process.
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
exper_name |
1 |
Experiment name |
char |
|
|
Typically will be the standard 6-char experiment designator (example. RDWPS1 ) |
exper_description |
1 |
Experiment description |
char |
|
|
|
exper_nominal_start |
1 |
Epoch of nominal experiment start |
epoch |
|
|
|
exper_nominal_stop |
1 |
Epoch of nominal experiment end |
epoch |
|
|
|
PI_name |
1 |
PI name |
char |
|
|
|
PI_email |
1 |
PI e-mail address |
char |
|
|
|
contact_name |
1 |
Contact name |
char |
|
|
|
contact_email |
1 |
Contact e-mail address |
char |
|
|
|
scheduler_name |
1 |
Scheduler name |
char |
|
|
|
scheduler_email |
1 |
Scheduler e-mail address |
char |
|
|
|
target_correlator |
1 |
Target correlator |
char |
VLBA ¦ VSOP ¦ JIVE ¦ Haystack ¦ etc. |
|
Others may be added. |
$FREQ
Block
The
$FREQ
block describes the signal and sampling characteristics the channels recorded on the tape, where a 'channel' is defined as a single USB or LSB output from a BBC. This includes such information as total RF sky frequency, sideband, channel bandwidth, sampling rate and bits/sample. The
$FREQ
block does not attempt to describe the recording mode, since the same set of channels may be recorded in different recording modes (or on different equipment) at different stations. Each frequency channel is defined by a
chan_def=
statement with at least 8 fields in each statement. The capability of specifying frequency switching is also built into the
chan_def=
statement by assigning each frequency channel to one or more numbered 'states'. The
switching_cycle=
statement then specifies the length of time spent in each of the states.
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
chan_def |
1 |
'Band_ID': RF band name |
&link |
|
|
Link to selected $SOURCE 'def' where it may be used to describe source-structure characteristics for scheduling purposes. May be omitted if not relevant. |
|
2 |
RF sky frequency at 0Hz in the BBC output |
real |
|
freq |
This frequency, in combination with the LO frequency specified in the $IF block allows computation of the BBC LO frequency for this channel. |
|
3 |
Net sideband of this BBC channel |
char |
U ¦ L |
|
Note that this will be opposite the labeling on the BBC itself if the IF going into the BBC is net LSB |
|
4 |
BBC Channel bandwidth |
real |
|
freq |
|
|
5 |
'Chan_ID': Logical channel name |
&link |
|
|
Must be different for each channel. Used as link to selected $TRACKS 'def'. |
|
6 |
'BBC_ID': Logical BBC name |
&link |
|
|
Link to selected $BBC 'def where connection to physical BBC is made. |
|
7 |
'Phase-cal_ID': Logical phase-cal name |
&link |
|
|
Link to selected $PHASE_CAL 'def' block to specify details of phase-cal tone(s). Null specifies no phase-cal to be detected. |
|
(8,9,...) |
Frequency-switched state numbers in which this channel is active |
int |
|
|
Used only with frequency switching. Specified state numbers are separated by colons. States must be ordered 1,2,... |
switching_cycle |
1 |
Phasing of frequency-switch cycle |
char |
wrt_obs_start ¦ wrt_min_mark |
|
Relevant only if frequency-switching being used. Timing of switching cycle begins according to this specification. |
|
2 |
State 1 period |
real |
|
time |
Interval over which state 1 is active |
|
3... |
State 2 period, etc |
real |
|
time |
Interval over which state 2 is active, etc. |
sample_rate |
1 |
Sample frequency |
real |
|
sample rate |
Ignored for S2. |
Notes:
- There must be one
chan_def=
statement for each BBC channel to be recorded.
- If one or more stations in an experiment observe different sets of frequency channels, there must be a separate 'def' for each different set of channels.
- A resolved link must exist for every specified 'linkword' in each
chan_def=
statement.
$HEAD_POS
Block
The
$HEAD_POS
block defines the headstack positioning as a function of 'headstack-position reference number' for Mark IIIA, Mark IV, and VLBA systems; the
$HEAD_POS
block is irrelevant for other types of recording systems.. One
headstack_pos=
statement is required for each potential headstack position (or set of positions if multiple simultaneous recording headstacks).
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
headstack_pos |
1 |
Position reference number |
int |
>0 |
|
|
|
2 |
Headstack 1 position |
int |
range of headstack motion |
length |
Allowed range depends on system, but is typically -1000 to +1000 um. |
|
(3) |
Headstack 2 position |
int |
range of headstack motion |
length |
Required only if headstack 2 is being used. |
|
(4) |
Headstack 3 position |
int |
range of headstack motion |
length |
Required only if headstack 3 is being used. |
|
(5) |
Headstack 4 position |
int |
range of headstack motion |
length |
Required only if headstack 4 is being used. |
$IF
Block
The
$IF
block defines the IF bands used in the observations and is linked to the
$BBC
block (which specifies the detailed BBC-to-IF connections). An
if_def=
statement must be defined for each of the IF 'links' specified in the selected
$BBC
'def'.
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
if_def |
1 |
'IF_ID' link word |
&link |
|
|
One if_def= statement must be present for each separate IF. |
|
2 |
Physical IF name |
char |
|
|
System dependent. Used to create procedures to select proper IF. See Notes. |
|
3 |
Polarization |
char |
R ¦ L |
|
|
|
4 |
Total effective LO of IF (just before signal enters BBC) |
real |
|
freq |
Positive number |
|
5 |
Net sideband of IF |
char |
U ¦ L |
|
|
|
(6) |
Phase-cal frequency interval |
real |
|
freq |
Typically 1 or 5 MHz. Null or omission indicates no phase-cal. |
|
(7) |
Phase-cal base frequency |
real |
|
freq |
Usually 0, in which case may be null or omitted. |
Notes:
- The 'total effective LO' is used in conjunction with the total sky frequency specified for each channel in the
$FREQ
block to calculate the local-oscillator setting in each individual BBC.
- The 'Physical IF Name' is a system-dependent designation specifying which IF is selected. For the VLBA system, IF's A, B, C, and D may each be selected with either a 'Normal' or 'External' input, leading to designations
AN
, AE
, BN
, BE
, CN
, CE
, DN
, and DE
. For the Mark III system, IF's 1, 2, and 3 may each be selected with either a 'Normal' or 'Alternate' input, leading to the designations 1N
, 1A
, 2N
, 2A
, 3N
, 3A
.
$PASS_ORDER
Block
The
$PASS_ORDER
block defines pass and group ordering relevant for Mark IIIA, Mark IV, VLBA and S2 systems. For Mark IIIA, Mark IV and VLBA system, each pass is defined by a two-part field composed of a numeric 'headstack-position reference' (defined in the selected
$HEAD_POS
'def') followed by an alphabetic 'subpass identifier' (defined in the selected
$TRACKS
'def'), e.g.,
2A
. For S2, the
S2_group_order=
statement defines the order of usage of tape groups.
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
pass_order |
1 |
First pass ID |
char |
|
|
e.g., 1A . First pass assumed to be in 'forward' direction. For S2, specified group#. |
|
2 |
Second pass ID |
char |
|
|
e.g., 2A |
|
... |
etc |
|
|
|
|
S2_group_order |
1 |
First group number |
int |
|
|
Specifies order in which S2 groups are to be recorded. |
|
2 |
Second group number |
int |
|
|
|
|
... |
etc |
|
|
|
|
Notes:
- The number of fields present in the
pass_order=
or S2_group_order=
statements specifies the number of tape passes or groups. Number of cassettes per group is defined by recording mode specified in $TRACKS
section. S2 groups are numbered starting at 0.
- First pass is assumed to be in the forward-tape-motion direction (Mark IIIA, Mark IV, VLBA).
$PHASE_CAL_DETECT
Block
The
$PHASE_CAL_DETECT
block is used to specify the phase-cal tones to be detected at the observing station.
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
phase_cal_detect |
1 |
pcal_ID |
&link |
|
|
Links to a chan_def= statement in selected $FREQ def. |
|
2 |
Tone number (from DC edge of BBC output) |
int |
|
|
Tone number of first tone to be detected. See tone-number definition in Notes. |
|
(3) |
Tone number |
int |
|
|
Tone number of second tone to be detected |
|
... |
etc |
|
|
|
|
Note:
- The actual phase-cal frequencies are determined by the LO frequencies specified in the
$IF
and $FREQ
blocks.
- The phase-cal frequency spacing are specified in the
$IF
block.
- Tone number 1 is defined as first tone above 0Hz in the BBC output channel, etc. Phase-cal detection will be done on the set of specified 'tone#'s, which are listed in order of preference in case more tones are specified than can be detected by the hardware. The tones are numbered positively from the low (DC) edge of the BBC output band, with tone number
1
being the first tone above DC. Tones may also be specified as negative numbers corresponding to their position from the nominal band edge, with tone number -1
being the first tone below nominal band edge. A tone number of 0
specifies state counting, rather than phase-cal detection, should take place.
$PROCEDURES
Block
The
$PROCEDURES
block specifies parameters relevant to various procedures at an observing station. Timing parameters are to be used as constraints to the scheduling program. The set of timing parameters listed is for the NASA 'sked' program. Other scheduling programs may use these and/or other parameters.
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
tape_change |
1 |
Tape-change time |
real |
|
time |
Required parameter |
headstack_motion |
1 |
Time to complete headstack motion |
real |
|
time |
Required parameter |
new_source_command |
1 |
Time to initiate pointing to new source |
real |
|
time |
Required parameter |
new_tape_setup |
1 |
Time to setup system for new tape |
real |
|
time |
Required parameter |
setup_always |
1 |
Setup system for each observation |
char |
on ¦ off |
|
Optional procedure |
|
2 |
Time to setup system |
real |
|
time |
|
parity_check |
1 |
Do parity check |
char |
on ¦ off |
|
Optional procedure |
|
2 |
Time needed to do parity check |
real |
|
time |
|
tape_prepass |
1 |
Do tape prepass |
char |
on ¦ off |
|
Optional procedure |
|
2 |
Time needed to do tape prepass |
real |
|
time |
|
preob_cal |
1 |
Pre-observation calibration |
char |
on ¦ off |
|
Optional calibration procedure |
|
2 |
Time needed for procedure |
real |
|
time |
|
|
3 |
Procedure name |
char |
|
|
|
midob_cal |
1 |
Mod-observation calibration |
char |
on ¦ off |
|
Optional calibration procedure |
|
2 |
Time needed for procedure |
real |
|
time |
|
|
3 |
Procedure name |
char |
|
|
|
postob_cal |
1 |
Post-observation calibration |
char |
on ¦ off |
|
Optional calibration procedure |
|
2 |
Time need for procedure |
real |
|
time |
|
|
3 |
Procedure name |
char |
|
|
|
procedure_name_prefix |
1 |
Specify standard procedure library |
char |
|
|
Specifies that a 'standard' procedure library is to be used. |
Notes:
- The
procedure_name_prefix
parameter is intended to allow the specification of frequently-used procedure libraries that individual stations may have honed to their particular requirements. For instance, the geodesy community frequently uses the same station setup over and over again (e.g., so-called 'SX2C' setup). The specification of the 'standard procedures' for a station relieves the requirement of creating a new set of procedures for an experiment.
$ROLL
Block
The
$ROLL
block defines the barrel-rolling sequence that may be used in VLBA and Mark4 recording systems. It is intentionally defined in a very general way, but for the most part will probably be confined to a few 'canned' modes.
The roll sequence is specified with a
roll=
statement for each track participating in the barrel roll, plus statements defining the roll period and reinitialization interval.
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
roll |
1 |
Roll on/off |
char |
on ¦ off |
|
Optional. See Notes. |
roll_def |
1 |
Headstack # |
int |
1-4 |
|
|
|
2 |
Home track |
int |
track # |
|
Track# that would be written in the absence of barrel-roll. |
|
3 |
Step 0 destination track |
|
|
|
Track to which home track is written when barrel-roll is initialized (step 0) |
|
4 |
Step 1 destination track |
int |
track # |
- |
Track to which home-track is 'switched' on first increment of barrel-roll. |
|
5 |
Step 2 destination track |
int |
track # |
- |
Track to which home-track is 'switched' on second increment of barrel-roll. |
|
etc |
|
|
|
|
|
|
n+2 |
Last-step destination track in n-step sequence |
int |
track # |
- |
Track to which home-track is 'switched' on last step of barrel-roll. Returns to Step 0 as next step. |
roll_inc_period |
1 |
Roll increment period in frames |
int |
|
(frames) |
|
roll_reinit_period |
1 |
Roll-sequence reinitialization period in seconds (at recording) |
real |
any |
time |
Fixed at 2 sec for VLBA. Mark4 can be specified. |
Notes:
- Barrel-roll is confined to tracks 2-33 within a given headstack. For cases of barrel-roll using multiple headstacks, the roll sequence definition must include all headstacks.
- Barrel-roll is applied in the formatter as the last step before the data are written to tape.
- System tracks do not participate in barrel-roll.
- The number of fields in the
roll=
statements defines number of positions in the roll sequence. All roll=
statements must specify the same number of positions in the roll sequence.
- Note that all track# references elsewhere in the VEX file are to the 'home track#'.
-
roll=off;
is default. Presence of any roll_def=
statements implies roll=on;
.
$SCHEDULING_PARAMS
Block
The
$SCHEDULING_PARAMS
block specifies various parameters needed for the scheduling program. Since each scheduling program may have its own unique set of parameters, the
$SCHEDULING_PARAMS
block is specified strictly as a literal block which must be parsed and interpreted by the relevant scheduling program. The parameters listed are some of those for the current version of the NASA 'sked' program. Other scheduling programs may use these and/or other parameters.
Note: These parameters are examples only!
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
sched_program |
1 |
Scheduling program name |
char |
|
|
|
|
2 |
Revision |
char |
|
|
|
default_scan_length |
1 |
Default scan length |
|
|
time |
|
lookahead |
1 |
Lookahead for source rise/set |
|
|
time |
|
min_scan_length |
1 |
Minimum scan length |
|
|
time |
|
minimum_between_scans |
1 |
Minimum time between scans |
|
|
time |
|
modular_scan_length |
1 |
Schedule on minute marks |
|
|
time |
|
max_display_width_col |
1 |
Display screen width |
|
|
(columns) |
|
confirm |
1 |
Confirm new scans |
|
on ¦ off |
|
|
mutual_vis |
1 |
Force all stations to see source, or allow subnet |
|
all ¦ subnet |
|
|
low_SNR_reject |
1 |
Reject stations if SNR too low |
|
auto ¦ man |
|
Primarily for geodesy |
variable_scan_length |
1 |
Use SNR calculation to set scan length |
|
on ¦ off |
|
Primarily for geodesy |
min_sun_angle |
1 |
Min angle between source and sun |
|
|
angle |
|
tape_usage_sync |
1 |
Synchronize tape usage |
|
on ¦ off |
|
|
sked_optimize |
1 |
Type or optimization for auto-scheduling |
|
sky_coverage ¦ covariance |
|
Primarily for geodesy |
window |
1 |
Sliding window for optimization |
|
|
time |
Primarily for geodesy |
maximize_num_obs |
1 |
Maximum total # of observations |
|
on ¦ off |
|
Primarily for geodesy |
minimize_idle |
1 |
Minimize idle time between scans |
|
on ¦ off |
|
Primarily for geodesy |
minimize_slew |
1 |
Minimize antenna slew time |
|
on ¦ off |
|
Primarily for geodesy |
$SEFD
Block
The optional
$SEFD
block allows the sensitivity of each IF to be modeled and used for a crude calculation of expected SNR when used with specified observing modes an d scan-length times. For geodesy, these calculations can be used to automatically adjust scan times for minimum-acceptable SNR in order to densify the schedule as much as possible. The particular SEFD model to be used can be specified, along with the model parameters.
$SITE
Block
The
$SITE
block describes the location of an antenna and may be either earth-based or earth-orbiting. Horizon masks for earth-based sites may be specified as an aid in scheduling.
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
site_type |
1 |
Type of site |
char |
fixed ¦ earth_orbit |
|
|
site_name |
1 |
Full site name |
char |
<=16chars |
|
|
site_ID |
1 |
Standardized 2-char site name |
char |
2 chars |
|
|
site_position |
1 |
x |
real |
|
length |
|
|
2 |
y |
real |
|
length |
|
|
3 |
z |
real |
|
length |
|
site_position_epoch |
1 |
Epoch of site_position |
epoch |
|
epoch |
|
site_position_ref |
1 |
Reference for site position |
char |
|
|
|
site_velocity |
1 |
x-velocity |
real |
|
speed |
|
|
2 |
y-velocity= |
real |
|
speed |
|
|
3 |
z-velocity= |
real |
|
speed |
|
horizon_map_az |
1..n |
List of azimuth values corresponding to values in horizon_map_el |
real |
|
angle |
Units specification may be omitted after first field. |
horizon_map_el |
1..n |
List of elevation limits at azimuths specified in horizon_map_az |
real |
|
angle |
Units specification may be omitted after first field. |
zen_atmos |
1 |
Zenith atmosphere added delay |
real |
|
time |
Typically on order of 7 nsec |
ocean_load_vert |
1 |
Ocean-loading vertical amplitude |
real |
|
length |
|
|
2 |
Phase |
real |
|
phase |
|
ocean_load_horiz |
1 |
Ocean-loading horiz amplitude |
real |
|
length |
|
|
2 |
Phase |
real |
|
phase |
|
occupation_code |
1 |
4-char occupation code |
char |
|
|
Primarily used for geodetic experiments |
inclination |
1 |
Earth-orbit parameter |
real |
|
angle |
|
eccentricity |
1 |
Earth-orbit parameter |
real |
|
- |
|
arg_perigee |
1 |
Earth-orbit parameter |
real |
|
angle |
|
ascending_node |
1 |
Earth-orbit parameter |
real |
|
angle |
|
mean_anomaly |
1 |
Earth-orbit parameter |
real |
|
angle |
|
semi-major_axis |
1 |
Earth-orbit parameter |
real |
|
length |
|
mean_motion |
1 |
Earth-orbit parameter |
real |
|
- |
|
orbit_epoch |
1 |
Earth-orbit epoch |
epoch |
|
epoch |
|
$SOURCE
Block
The
$SOURCE
block defines the sources to be observed and specifies their relevant characteristics, particularly position. A single source is defined in each 'def' block. A crude source model may be specified for each observed 'Band_ID' specified in the
$FREQ
block for purposes of auto-scheduling (primarily geodesy).
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
source_type |
1 |
Generic source type |
char |
star ¦ earth_satellite |
|
Specifies coordinate system in which position of object will be specified. Other types may be added. |
|
2 |
Experiment source type |
char |
target ¦ calibrator ¦ dummy |
|
dummy may be declared if the source if specified for pointing purposes only. Station field system may use this information. |
source_name |
1 |
Source name |
char |
<=16 char |
|
Typically same as 'def' label name (e.g., 3C273B ) |
For 'source_type=star':
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
IAU_name |
1 |
Standard IAU source ID |
char |
9-char |
|
Example: 0102-0304 |
source_position_ref |
1 |
Origin of source position |
char |
<=16-char |
|
For traceability of source position |
ra |
1 |
Right-ascension |
RA |
|
RA |
Example: 01h02m03.456s |
dec |
1 |
Declination |
dec |
|
dec |
Example: -03d04'05.678" |
ref_coord_frame |
1 |
Source-position reference frame |
char |
B1950 ¦ J2000 |
|
|
ra_rate |
1 |
RA proper motion |
real |
|
ang rate |
Typically asec/yr |
dec_rate |
1 |
Declination proper motion |
real |
|
ang rate |
Typically asec/yr |
source_position_epoch |
1 |
Epoch of stated position |
epoch |
|
epoch |
Needed only if non-zero ra_rate or dec_rate |
source_model |
1 |
Component number |
int |
|
|
One source_model= statement for each major source component for each 'Band_ID' link to the selected $FREQ 'def' |
|
2 |
'Band_ID' linkword to selected $FREQ 'def' |
&link |
|
|
|
|
3 |
Component flux-density |
real |
|
flux-density |
|
|
4 |
Component major axis |
real |
|
angle |
Angle subtended on sky |
|
5 |
Component axis ratio |
real |
|
|
|
|
6 |
Component position angle |
real |
|
angle |
|
|
7 |
Component RA offset wrt specified source position |
real |
|
angle |
|
|
8 |
Component dec offset wrt specified source position |
real |
|
angle |
|
For 'source_type=earth_satellite':
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
inclination |
1 |
Orbit inclination |
real |
|
angle |
|
eccentricity |
1 |
Orbit eccentricity |
real |
|
|
Unitless |
arg_perigee |
1 |
Argument of perigee |
real |
|
angle |
|
ascending_node |
1 |
Longitude of ascending node |
real |
|
angle |
|
mean_anomaly |
1 |
Orbit mean anomaly |
real |
|
angle |
|
semi-major_axis |
1 |
Orbit semi-major axis |
real |
|
length |
|
mean_motion |
1 |
Orbit mean motion |
real |
|
|
|
orbit_epoch |
1 |
Epoch of stated orbit |
epoch |
|
epoch |
|
$TAPELOG_OBS
The
$TAPELOG_OBS
block contains information about the media (disks or tapes currently) that were used during the experiment. This table is normally appended after the completion of an experiment. Each station can have multiple media listed which can in principle overlap in time if parallel recording occurred.
Parameters in this table are:
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
VSN |
1 |
Recorder number |
int |
|
|
|
|
2 |
Volume Serial Number (VSN) |
char |
|
|
8 character string, conventionally all capital |
|
3 |
Start time |
epoch |
|
epoch |
Epoch when this disk/tape started |
|
4 |
Stop time |
epoch |
|
epoch |
Epoch when this disk/tape stopped |
$TRACKS
Block
The
$TRACKS
block defines the various multiplex (fan-in and fan-out) modes that can be used to record data on the
Mark3A, Mark4, VLBA and LBA DAS's. In cases where a mode uses fewer than the full number of heads in a single pass, alphabetical 'sub-passes' are defined (tape passes with the headstacks in a fixed position).
For purposes of multiplex definitions, the sample data from each channel are separated into a 'sign' bitstream and (for 2-bit sampling) a 'magnitude' bitstream.
The fan-out modes (single bitstream to 1, 2 or 4 tracks) are defined with a set of
fanout_def=
statements, one such statement for each bitstream and subpass, which defines the destination tracks and bit ordering among the tracks. In this way a complete definition of the multiplex format is specified. The 'ChanID' linkword in each
fanout_def=
statement connects a particular bitstream to the selected 'def' in the
$FREQ
block.
The fan-in modes (1, 2 or 4 bitstreams to a single track) are defined by a set of
fanin_def=
statements. Each such statement defines the bitstreams written to a single track in a specified subpass. The set of 'ChanID' linkwords in each
fanin_def=
statement connects the particular bitstreams to the selected 'def' in the
$FREQ
block. and specifies their multiplex order on the track.
Within each
fanout_def=
or
fanin_def=
statement is a field which specifies the 'sub-pass' to which it applies. A 'subpass' is defined as a single tape pass for which the headstack(s) are held at a fixed position. Typically, for example, 16 of 32 tracks may be written in a single tape pass; for this case there are 2 sub-passes with a given headstack position. By convention, the subpasses are labeled A, B, C, ....,etc.
Note that, except for the
VLBA_trnsprt_sys_trk=
statement, all references to 'track numbers' in the
$TRACKS
block are more properly labeled as 'home tracks' since barrel-rolling in the formatter (Mark 4 and VLBA) and track switching within the recorder (VLBA only) may lead to modified physical track assignments. Normally, the actual physical track numbers (pre-barrel-rolled) correspond identically to 'home track' numbers.
Parameter |
Field |
Description |
Type |
Allowed values |
Units |
Comments |
fanout_def |
1 |
Sub-pass ID |
char |
single char |
|
One fanout_def= statement required for each bitstream. By convention, subpass_ID uses characters A, B, C, etc. Null for Mark 5A and LBA. |
|
2 |
'Chan_ID' linkword |
char |
- |
|
Link to 'Chan_ID' in selected $FREQ def |
|
3 |
Sign or magnitude bitstream |
char |
sign ¦ mag |
|
Fields 2 and 3 uniquely define a single bitstream |
|
4 |
Headstack number |
int |
1-4 |
|
|
|
5 |
First multiplex track |
int |
track# |
|
Track # within headstack |
|
(6) |
Second multiplex track |
int |
track# |
|
Required for fanout 1-to-2 or 1-to-4 |
|
(7) |
Third multiplex track |
int |
track# |
|
Required for fanout 1-to-4 |
|
(8) |
Fourth multiplex track |
int |
track# |
|
Required for fanout 1-to-4. Number of fields specifies fan-out ratio. |
fanin_def |
1 |
Sub-pass number |
int |
single char |
- |
By convention, uses characters A,B,C,...etc. |
|
2 |
Headstack number |
int |
1-4 |
|
|
|
3 |
Track number |
int |
track# |
|
|
|
4 |
'Chan_ID' linkword for multiplex bitstream 1 |
char |
|
|
Link to 'Chan_ID' in selected $FREQ def |
|
5 |
sign or magnitude bitstream (of 'Chan_ID') |
char |
sign ¦ mag |
|
Fields 4 and 5 uniquely define the bitstream which occupies bit position 1 on the specified track. |
|
(6) |
'ChanID' linkword for multiplex bitstream 2 |
char |
|
|
Fields 6 and 7 required if fanin is 2-to-1 or 4-to-1 |
|
(7) |
sign or magnitude bitstream |
char |
sign ¦ mag |
|
Fields 6 and 7 uniquely define the bitstream which occupies bit position 2 on the specified track. |
|
(8) |
'ChanID' linkword for multiplex bitstream 3 |
char |
- |
|
Fields 8 and 9 required if fanin is 4-to-1 |
|
(9) |
sign or magnitude bitstream |
char |
sign ¦ mag |
|
Fields 8 and 9 uniquely define a bitstream which occupies bit position 3 on the specified track. |
|
(10) |
'ChanID' linkword for multiplex bitstream 4 |
char |
|
|
Fields 10 and 11 required if fanin is 4-to-1 |
|
(11) |
sign or magnitude bitstream |
char |
sign ¦ mag |
|
Fields 10 and 11 uniquely define a bitstream which occupies bit position 4 on the specified track. |
track_frame_format |
1 |
Frame format on tape track |
char |
Mark3A ¦ Mark4 ¦ VLBA |
|
Mark3A and Mark4 are slightly different data-replacement formats. VLBA is non-data-replacement format. VLBA can write Mark3A format. |
data_modulation |
1 |
Pseudo-random data modulation |
char |
on ¦ off |
|
Default is 'off'. |
VLBA_frmtr_sys_trk |
1 |
Formatter 'system' track# to be written with specified data |
int |
0 ¦ 1 ¦ 34 ¦ 35 |
|
Applicable to VLBA formatter only. Specifies data to be written to a particular 'system' track formatter outputs. |
|
2 |
Data type to be written to system track specified in Field 1 |
char |
xtk_parity ¦ duplicate |
|
xtk_parity if cross-track parity to be written; duplicate is this track is to duplicate one of the normal data tracks. |
|
3A |
If Field 2 is xtk_parity : First track# of contiguous set of tracks covered |
int |
2 ¦ 10 ¦ 18 ¦ 26 |
|
Limited to specified set of 'first track #'s' |
|
4A |
If Field 2 is xtk_parity : #tracks covered by cross-parity |
int |
8 ¦ 16 |
|
|
|
3B |
If Field 2 is duplicate : 'home track#' of data to be written to specified 'system' track# |
int |
2-33 |
|
Will always be 'home track' data; is not barrel-rolled |
VLBA_trnsprt_sys_trk |
1 |
Physical 'system' track (head#) to be written as a duplicate of specified formatter output track (recorder input track).. |
int |
0 ¦ 1 ¦ 34 ¦ 35 |
|
This is a duplication within the transport itself, so includes all barrel-roll |
|
2 |
Formatter output track (recorder input track) to be duplicated |
int |
2-33 |
|
|
S2_recording_mode |
1 |
Recording mode ID |
char |
See Notes |
|
Example: '32x4-2' |
S2_data_source |
1A |
Define S2 data source |
char |
Mark4_formatter ¦ VLBA_BBC_1-4 ¦ VLBA_BBC_5-8 |
|
Relevant for S2 only |
|
1B |
Define LBADR bit encoding |
char |
VLBA ¦ VSOP |
|
Relevant for LBADR only. VSOP encoding is mag/sign, VLBA encoding is offset binary |
|
2 |
Define BBCx selection from Mark 4 formatter |
&link |
|
|
For Mark IV only: Link to 'BBC_ID' in $FREQ . See Notes. |
|
3 |
Define BBCy selection from Mark 4 formatter |
&link |
|
|
For Mark IV only: Link to 'BBC_ID' in $FREQ . See Notes. |
Notes:
- Reference to Mark IV Memo 230 (aka VLBA Acquisition Memo 393) may help to clarify the details of multiplex and signal switching in the Mark IV and VLBA systems.
- The actual fanin/fanout ratio is implied by the number of subfields in the
fanout_def
or fanin_def
statements, as indicated in the above table.
- For a fanin/fanout ratio of 1-to-1 (i.e. one bitstream to one track), either
fanout_def
or fanin_def
statements may be used.
- Cross-track parity is computed after barrel-rolling as the last step before writing to tape.
- The 'S2_recording_mode' parameter specifies the recording mode to which the S2 system is to be set. The available modes are documented in 'S2-RT User's Manual, Version 3.0 (162)', October 1996, ISTS-SGL-TR96-033, available at
ftp://s2.sgl.ists.ca
. The selected mode defines the number of recording 'groups' and recorded inputs. The S2_group_order
parameter in the $PASS_ORDER
section specifies the order in which the groups are to be recorded.
- The 'S2_data_source' parameter specifies the origin of the sampled data recorded by the S2 recording system. Typical data sources are either through the so-called 'phase-cal' outputs of the Mark IV formatter or direct sampler outputs from the VLBA system. This keyword was reused with a different meaning for electronics_rack_type=LBA.
Mark IV formatter : the sampled data from the USB and LSB outputs of each of two selected BBC's can be directed to the 'phase-cal output'. The data available to the S2 are unformatted 2-bit samples at 32 Msamples/sec, regardless of the sample rate chosen for output to the Mark IV recording system. If we designate the two selected Mark IV BBC's as BBCx and BBCy, the Canadian VIA (VLBI Interface Adapter) implements a fixed mapping to S2 inputs as follows:
VLBA samplers : the input to the Canadian VIA box may be taken either from BBC's 1-4 or BBC's 5-8, depending on the physical connector to which it is attached. The mapping within the VIA is fixed, as follows:
The information in the above tables is taken from the 'VLBI System Interface Adapter (VIA) User's Manual, Ver. 1.3', ISTS/SGL, October 25, 1996, available at
ftp://s2.sgl.ists.ca
.