Software

The software used by the Dwingeloo telescope at present is described in more detail in Galactic Observations with the Dwingeloo Telescope. This is available from Henny Lem.

Schedule format

The schedule is an ASCII text file where the 3 different types of input of parameters are entered in in 3 phases:

Bit options.

These consists of lines on numbers with commas. It ends with -1

Program steering and correlator options.

These have lines of 2 letter codes or numbers separated by commas and end with GO, BA or HO.

Telescope steering.

This has lines of numbers separated by commas. You can go to level 1 with -1 or HO.

The default action at the end of a schedule is to go back to the first level and repeat the schedule.

See the section Example schedule

Bit options (Phase 1)

Bits can be set (value =1 = true ) or unset (value =0 = false). Default values are off at the start of input, but once set they remain set during the rest of the session until explicitly unset. The syntax is:

bit number,value

Here are a list of bit numbers, followed by them meaning of the code value.

0

Wait for switch '0' in telescope. The hardware no longer exists for this option so do not use it, so its value must be left at 0.

1

Do not wait 1 second before starting correlator. This is used for the scan mode.

2

Combine bits 2 and 3 to specify the noise tube value.

3

(see 2) Code for noise tube value (in K)

'10'=5K '11'=0.5K '01'=50K

Note that in the current 21cm frontend there is only one noise tube with the nominal value of 15K, so the value given for these parameters is irrelevant.

4

Not used.

5

Sidereal clock unavailable: This is at present TRUE, but the default is off (i.e. ST clock available).

6

not used

7

UT clock unavailable: This is at present FALSE, which is the default setting.

8

Suppress log output. This is seldom used except for pointing mode obervations where the log output can be excessively long.

9

Frequencies given by FR (see the phase 2 input) are rest values. Calculate true ones based on velocity in the LSR frame given with the VO value. If this bit is not set then no correction for velocity is made.

10

not used

11

not used

12

Control rotator: This must at present be left as FALSE as the rotator hardware is not operational.

13

Store data to disk: This is normally set to TRUE, so that the data can be later inspected and exported.

14

Store data to tape. This is normally left FALSE as data is normally written to disk. Clearly one of the bits 13 and 14 must be set on, or no data is taken. If neither is set on an error code is given.

15

Interrupt a subscan, finish the cycle, do not store the data, and continue with next scan . This is used to interrupt running schedules, by running the program REGIS.

-1

End of input phase 1; continue to phase 2.

Letter codes (input phase 2)

These are usually specified but some default values are available from a file called `INFOFL'. This file can be filled offline by the program INFFL (see below) and the values used are updated where and when necessary during observing. Values specified locally override those defaults. The syntax is:

code
optional values

If a code has no values then it is just followed by the next piece of schedule. To exit phase 2 give the parameter GO (see below).

BA

Go back to bit settings (input phase 1).

CH

Number of correlator channels to use. The default is 1024 for single spectra at bandwidths <40MHz and 512 for double spectra or 40MHz bandwidth.

CR

Set up subcommands C1,C2,C3,CL, which steer the correlator configuration.

C1

Set the bandwidth codes: 4 values are needed, as given in this table.

-2

40MHz (only 512 frequency channels possible).

-1

20MHz The usual one for HI surveys.

0

10MHz

1

5MHz

2

2.5MHz

3

1.25MHz

4

0.625MHz

5

0.3125MHz

6

0.15625MHz

7

0.078125MHz

Make sure that the hardware is setup to correspond to any settings given See section Hardware. The 4 values correspond to 2 IFs each of which can, in some correlator configurations, be operated in split mode, see section Observing modes. Note that the hardware allows double spectra for bandwidths less than 20MHz.

C2

Set the correlator parameters. This is sent as an octal number prefixed by @. Each octal digit has a special meaning:

0

Cross or autocorrelation: Use 0 only, as cross correlation is not possible.

1

Single/double spectrum: 0 is a single spectrum and 1 is a double spectrum.

2

1bit/2bit mode: 2 or 4 , where 2 is one-bit (2-level) and 4 is two-bit (4-level).

3

Number of clock levels: This is always 2.

4

Cycle mode. If we denote the various parts of the observation as:

s=signal, r=reference, n=noise

then the modes available are:

0

s

1

r+n, r

2

s,s+n

3

s,s+n,r+n,r

4

r+n,r

5

s,s+n

6

s,s+n,r+n,r

Modes 0,1,2, and 3 are for test purposes only. Modes 4,5, and 6 do not integrate with the noise tube on. Mode 4 is used with reference fields. Mode 5 is normal and 6 is used for frequency switched observations. A typical value is @52400, which makes 2-bit spectra, but there are other possible values.

C3

Data collecting parameters

• Subscan time (seconds). The minimum subscan time for the correlator and its hardware has been set at 25seconds, so the cominbination of (total subscan integration time)x(noise tube fraction) must be greater than 25seconds. Typical values are from 80 to 840.
• Number of cycles: only 1 can be used at present.
• Number of subscans/scan. This is normally 1 as subscans are not currently used.

CL

Return to main mode

DA

Year minus 1900. The default is taken from the file `INFOFL', but note that schedules running around newyear should set this parameter.

EQ

Use the equation of equinoxes. This is only relevant if the ST clock unavailable (currently TRUE).

FR

Frequencies (in MHz). Order is:

• Freq 1
• Shift in freq 1
• Freq 2
• shift in freq 2

Note the influence of the velocity specified by VO if bit 9 is on.

GM

Fraction of time for noise injection default=0.125.

GO

Continue to give telescope pointings in input phase 3.

HO

Stop program right away. This is used at the end of all pointings given by phase 3 (see below).

RD

Number of channels to reduce. Default is same as observed. It cannot be more, as this gives an error.

RE

Record number in which to store next data. If specified it overwrites the value in the file `INFOFL'. This option is normally not used except as to recover after some type of system crash.

RG

Tracking a grid mode for pointing observation.

SG

This is a special mode with offsets in azimuth and elevation (telescope pointing parameters 14 and 15). This mode is rarely used.

TG

Tracking a grid mode (normal)

TR

Scanning mode for pointing observation: DO NOT USE

TS

Scanning mode: DO NOT USE

RO

Dipole rotator position in degrees. This is not relevant as the rotator hardware is not operational, and the system waits for rotator.

RR

Reset the dipole rotator. This item is not relevant (see RO).

SE

Search tape for end-of-file. If not given, the data goes to the beginning of tape and overwrites anything previously there. This command must be after RG,SG,TG,TR, or TS.

SN

Scan number. This item is not needed, except for recovery after a crash,as the correct value is normally read from the file `INFOFL'.

SY

The frontend mixing scheme code setup (See section Hardware). This item must have 6 parameters (one set of 3 for each IF). If it is not specified then the value is read from the file `INFOFL'. Note that the software specification must agree with the hardware implementation.

TI

Start/Stop times. This can optionally be entered for each measurement. If observations are time critical, then the values must be given in the following order:

1. start day
2. start hour
3. start minute
4. margin for start time in minutes. Must be less than 60 The observation can start within + or - this margin.
5. maximum wait time in minutes. Must be less than 720
6. end day
7. end hour
8. end minute

The system depends on which clock is used (at present only the UT clock is available). The `day' quoted is the (UT) day number, so that for every year 1 January = day1, and the day number increases by 1 per day until 31 December (=day 365, except for leap years where it is 366).

VO

Source velocity in km/s in the LSR (Local Standard of Rest) frame with the 'radio' definition. This is used to calculate the observing frequency if bit 9 is set. Please note that a value of zero is not the same as no correction. No other velocity reference frame is supported. (7) The program expects a 'real' value (i.e. with decimal point).

Telescope parameters (input phase 3)

To get to input phase 3, we must first specify GO in input phase 2. Parameters 1 to 11 must be specified; 12 to 15 are only needed in special cases. A missing parameter means same as last time, except for parameters number 1,12 and 13 (NG,ST and DT) which are not saved, but CHINP will not count them. Values are given in degrees unless otherwise noted. The syntax is a line with a comma-separated list of values; to go to input phase 2 give a line with the value -1, just as is done for input phase 1.

The parameters are as follows:

1. NG, number of times to repeat the whole grid (as specified by parameters 4 to 11). See also parts 7-11
2. LL, lower limit for elevation in degrees. default: 2
3. UL, upper limit for elevation in degrees. default: 86
4. CC, coordinate code:
   1. RA,dec of date (apparent coordinates)
   2. l,b (galactic coordinates)
   3. RA,dec of epoch 1950
   4. HA,dec
   5. (not used)
   6. (not used)
   7. (not used)
   8. azimuth,elevation (used for tests and maintainance only)
5. XX, X start coordinate
6. YY, Y start coordinate
7. DX, distance in X coordinate between grid points
8. DY, distance in Y coordinate between grid points
9. MX, Number of X grid points
10. MY, number of Y grid points
11. FC, Direction of first grid movement (0=X, 1=Y)
12. ST, time to start the correlator after reaching first grid point (deg)
13. DT, delta time (deg) to start correlator at the next next grid point. Note that the integration times as given in C3 in input phase 2, and the ST and DT parameters depend on one another.
14. OA, azimuth offset ( for SG mode)
15. OE, elevation offset ( for SG mode)

Operational software

A description of this is given in Galactic Observations with the Dwingeloo Telescope. Many control parameters are in the RT (Real Time) common area. Some are inputs and some are calculated by the programs.

Online software

The following list gives the online programs:

OBSRV

This program initiates parameters, reads an input file stores information in the RT common area and starts programs. When run it asks for a file name with the observing parameters, and gives the bit settings. When it finishes it writes a summary of what it has done on the line printer. To break off, use :

BR,OBSRV

FREQU

This calculate observing frequencies. This is scheduled by OBSRV and parameters are passed in a SAM buffer. {SAM is System Available Memory }

STUUR

This program controls telescope pointing. This is scheduled by OBSRV and calculates the demanded azimuth and elevation every 5seconds for the coming ten seconds and puts in pointing corrections. Between these new values every 5 seconds, a steering command is sent out based on an interpolation every 0.2seconds.

DWCON

This program controls the correlator This is scheduled once at the start of a run by OBSRV to setup the correlator mode ams start integration, and is run during observations to check that the correlator settings are correct. See NFRA note 505.

CLLCT

Schedules DWDAT and on a regular basis and writes blocks of 256 bytes to disk. One logical record is 4352 bytes long. This consists of 172 bytes of administration and 4180 bytes of correlator output. One file can have 32767 logical records, and after that the records get recycled. This data is buffered and only written to disk at the end of a subscan.

DWDAT

This program reads out the correlator. It is scheduled by CLLCT. See NFRA note 505.

REGIS

This program can set bits as used in input phase 1, so its main use is to interrupt an observation in progress. This is done by putting the value of parameter 15 to 1 , so stopping the current subscan. It can also be used to turn off logging for pointing mode observations.

STATE

Displays a summary of what is happenning in the observation now, as well as the expected time of ending.

Offline programs

BOOLO

Program for coordinate conversions; RA,dec of epoch to RA,dec of date, galactic coordinates, azimuth and elevation observing frequency, rising and setting times. This is mainly used in preparing a schedule.

CHINP

This program is to check the input parameters for OBSRV. It asks for an input file. It warns about syntax errors and any impossible parameter values (e.g. out of range) that it finds. You can continue past these errors, after noting the block number, by typing CO (for continue).

PLANN

This is used in planning a schedule, with rising and setting times, etc. Based on the input file for OSBRV. It checks for time lost in moving the telescope, but can underestimate time lost in frequency switching. It asks for the OBSRV file name and the pointing correction table. It assumes the telescope starts off pointing to the south. At present do not use this program.

INFFL

This updates or lists the file `INFOFL'. This file can also be written to by OBSRV and is read by OBSRV , CHINP, PLANN and INFFL. Some default values need to be changed occasionally, such as the year and frequency parameters.

CLEAR

Resets the tape unit.

HMSDG

Converts hh:mm:ss to degrees, and vice versa.

Test software

CTSTP

Correlator test. This is described in NFRA note 531.

RDCLK

Reads the console clock and sets computer clock

TESSY

Tests the synthesizer. You need to know the mixing scheme.

TLINK

Tests the multiplexer link.

TNOIS

Tests the noise tube switching.

TTEL

Tests the telescope pointing. It can also be used in emergencies to steer the telescope in azimuth and elevation.

AFRGL

Used to re-calibrate the telescope steering parameters (e.g. after a new motor or brake system is installed).

Output files

There are now 3 data files for galactic observations called GAFIL1, GAFIL2, and GAFIL3. Each can contain 32767 records. For each of the above files there is a log file called respectively OBLOG1, OBLOG2, and OBLOG3. Scan numbers are usually identical to record numbers in the files. There can be problems with observation which run over the boundary of the files, in which case some data will be overwritten.

Reduction software

GARED

This reduces data collected. See Galactic Observations with the Dwingeloo Telescope for a description of how to use it. Raw correlator output can calibrated and fourier transformed to make a spectrum, and it is possible to specify particular scans as references. The program can send a plot buffer to GAPLT for display.

GAPLT

This is called by GARED and makes plots.

GCOPY

This is the program used to export the observation to tape, or copy the observation to another disk file. The export format is unlabelled tape with fixed records of 4352 bytes.

TSYS

This program calculates System temperature as a check on the receiver behaviour.