Set-Up VERBS

The set-up VERBS are used to set up the frontend and backend configurations for data acquisition during an observation. OBS _E currently holds two set-ups in parallel, one for continuum, and one for spectral-line observations. Both set-ups remain stored until changed explicitly by one of the VERBS described in this chapter. Once set, either the continuum or line set up is automatically selected by the VERB that initiates an observation or calibration measurement.

C_MODE

  

OBSE  >  		 C_MODE   < c_mode  >  
		/DEFAULT 		 /BACKEND_C   < identification  > 
		/PHASES_C   < nr_of_phases  >  /RECEIVER_C   < rx_nr  >  
		/CYCLETIME_C   < t  >    < blank  >  /FREQUENCY_C   < GHz  >    < side  > 
		/SWITCHES_C   < static1  >    < static2  >    < switch number forCAL-Signal  > 

C_MODE sets up the frontend-specific part of the receiver for continuum observations and selects the backend. If parameters are entered as current values, they remain active until the verb is entered again, except the /DEFAULT adverb is used to tranfer the parameters into the default values.

• < c_mode > : The observing mode, which takes one of the possibilities: T, B, L, C, V, A, X, E,
  where T = Total-power, B = Beam-switched, L = Load-switched, C = Correlation, V = VLBI, X,A = VLBI-special and E = External mode.

  NOTE: The observing mode can be changed by every VERB executing a continuum observation, except SKYDIP. By the observing mode an adopted pattern for frontend-control switching and the formulas for the online display and the pendriver-outputs are selected.

ADVERBS:

• BACKEND_C sets the name of the continuum backend. Currently only the 80-channel digital backend can be used.
• PHASES_C is the number of receiver switch phases; typically 4.
• RECEIVER_C Frontend number to be connected. Currently frontend 1 is initialized by the operator and is selected automatically.
• CYCLETIME_C This sets the phase time (in msec) and the blanking time (in units of 10 $\mu$ sec) for the pulse generator within the Frontend control unit. Typical values are 16 40.
• FREQUENCY_C Sets the center frequency and the side-band for continuum observations. See the verb LINE if the frequency is to be extracted from a catalog.
• SWITCHES_C The frontend control unit has dynamic (driven by Dicke switching pulse generator) and static switches. The first 2 parameters set the static switches of the Frontend Control Unit. The dynamic switches are set as a function of the observing mode. The third parameter defines the position of the CAL switch for possible use in automatic calibrations.

CONTBACKEND

  

OBSE  >  		 CONTBACKEND
		    /DEFAULT		/CHANNELS_C   < number_of  >  
		    /BANDWIDTH_C   < not used  > 		/PREINTEG_C   < int  >    < cycles/DAP  > 
		    /PEN    < channel-nr  >   < channel-nr_of_Ref  > 

CONTBACKEND sets up the parameters for the continuum backend selected by C_MODE. If parameters are entered as current values, they remain active until the verb is entered again, except the /DEFAULT adverb is used to tranfer the parameters into the default values.

ADVERBS:

• CHANNELS_C is not any more implemented !
  It was used to set the number of backend channels in connection with the (old) 8-channel continuum backend.

  Continuum receivers are now connected to the 80-channel backend. Most receivers in the secondary focus are connected to channels permanently assigned to them. Only the first eight channels can be assigned for temporary use. The command BE80   allows to select those channels, which should deliver data for the observation.

  EXAMPLE:

   

  OBSE >

  BE80 CLEAR

  OBSE >

  BE80 1...4 , 7, 18

  At first all previously selected channels are cleared, then receiver channels 1 2 3 4 7 and 18 are selected to be stored in the raw data. In the archived data receiver channel 1 is archived channel 1, receiver channel 2 is 2 etc. ..., receiver channel 7 is archived channel 5 and receiver channel 18 is archived channel 6 on tape.
  NOTE: The sequence in the raw data is always in ascending order, independend in which order they are given.
  IMPORTANT:
  It is recommended first to clear (BE80 CLEAR) all selected channels before setting new ones otherwise they are added to the old defined channels. (More details on this command one can find in the OBSINP-manual).

• PREINTEG_C
  < int > sets the number of basic cycles that are averaged phase-wise before being transferred to disc, i.e. number of basic cycles per dump.

  < cycles/DAP > sets the number of full backend dumps that are stored before the time and position information of the drive program (DAPs) is added.

  EXAMPLE :

  OBSE >

  C_MODE /CYCL 16 40 /PHASE 5

  OBSE >

  CONTBACKEND /PRE 3 4

  This means that phases 1 to 5 have a duration of 16 msec each, and each successive set of 5 readouts are co-added with the first set until 3 cycles have been integrated (after 240 msec). At this point, the 5 phase values (each with an integration time of 48 msec) are dumped to disk. After four of these 240-msec data stretches of receiver output have been written sequentially to the raw-data file, they are followed by one set of data-associated parameters (DAPs), valid for the time at the end of the final integration, i.e. for 960 msec after the start of that portion of receiver output.

• BANDWIDTH_C Not yet implemented.
• PEN
  < channel-nr > sets the receiver-channel, which is used as output for the online pendrivers and also for the online display with the calculation of the gaussfit, if a POINTING is made. The formula, which is used, depends on the selected observing mode.
  

  < channel-nr_of_Ref > is used in beamswitch-mode as the receiver channel of the reference-beam by calculating the difference-signal.

L_MODE

  

OBSE  >  		 L_MODE   < l_mode  >  
		/DEFAULT 		/BACKEND_L    < backend_id  > 
		  /PHASES_L   < number  >  /RECEIVER_L   < rx_nr  > 
		 /CYCLETIME_L   < t  >    < blank  >  /FREQUENCY_L   < SCF  >    < side  > 
		 /SWITCHES_L   < static1  >    < static2  >    < switch-nr. for CAL-Signal  >   < NB  > 

• < l_mode > : The observing mode, which takes one of 3 possibilities: T, F, L,

  where T = Total-power, F = Frequency-switched and L = Load-switched mode.

  L_MODE sets up the frontend-specific part of the receiver for spectral-line observations and selects the backend. If parameters are entered as current values, they remain active until the verb is entered again, except the /DEFAULT adverb is used to tranfer the parameters into the default values.

  NOTE: The observing mode can be changed by every VERB executing a line observation.

ADVERBS:

• BACKEND_L Sets the name of the line backend. Currently only the autocorrelator backend can be used.
• PHASES_L Number of receiver switch phases.
• RECEIVER_L Frontend number to be connected. Currently only frontend 1 can be selected.
• CYCLETIME_L This sets the phase time (in msec) and the blanking time (in units of 10 $\mu$ sec) for the pulse generator within the Frontend control unit. Typical values are 500 1000.
• FREQUENCY_L Sets the center frequency and the side-band for line observations. See the command LINE if the frequency is to be extracted from a catalog.
• SWITCHES_L
  The frontend control unit has dynamic (driven by Dicke switching pulse generators) and static switches. The first 2 parameters set the static switches of the Frontend Control Unit. The dynamic switches are set as a function of the observing mode. The third parameter defines the number of the CAL switch for possible use in automatic calibrations.

  < NB > Noise balancing, tested for Y(es). Activates the injection of noise on the reference position (OFF the source), if the frontend is equipped to performe this function.

AUTOCORREL

  

OBSE  >  		 AUTOCORREL
		/DEFAULT 		/LEVELCONT   < contr  >  
		 /SPLIT   < split_mode  >    < doppler_mode  > 
		/AC_OPTIONS   < IF_conn  >    < quantization  >    < output_func  >  
		/CHANNELS_L   < IF_distribution  >  /PREINTEG_L   < dump_time  >  
		/BANDWIDTH_L   < f1  >    < f2  >    < f3  >    < f4  >  [unit]
		/FRQ_DOPPLER   < o1  >    < o2  >    < o3  >    < o4  >  [unit]
		/VEL_DOPPLER   < v1  >    < v2  >    < v3  >    < v4  >  [unit] 

Connects the 1024-channel autocorrelation spectrometer with the frontend, which is defined by the command L_MODE. If parameters are entered as current values, they remain active until the verb is entered again, except the /DEFAULT adverb is used to tranfer the parameters into the default values.

ADVERBS:

• SPLIT < split_mode > < doppler_mode > :

  < split_mode > (number) How to split the correlator bands

  
  		0:  1x1024 		1:  1x512 (100-MHz Bandwidth)
  		2:  1x768 + 1x256 (no FFT !) 		3:  2x512
  		4:  1x512 + 2x256 		5:  4x256
  		6:  2x256 + 1x512 		7:  1x256 + 1x768 (no FFT !)
  

  < doppler_mode > Frequency shift within a correlator band:
  Defines, if and how the values entered in FRQ_DOPPLER and VEL_DOPPLER should be used to calculate a shift of the correlator analyzing band with respect to the center of the IF band. These option might be handy especially when the correlator is split in more bands. Option 2 and 3 shift the correlator band by a fixed amount, typically used in frequency switching or testing for bad channels. Option DOVE centers the main line frequency (FREQUENCY_L) on different velocity windows, option DOFR uses the source velocity and centers the bands at different line frequencies (ex. isotops), the option DOFV allows the different lines and different velocities. In the latter case the FREQUENCY_L should be set to optimize the IF band. If the frequencies are to be used for a recalculation of the sky frequency (DOFR or DOFV), they are treated as offsets to the FREQUENCY_L if there absolute value is below 200 MHz.

  NONE: No frequency- or velocity-offset is used
  OFFR: Offset in frequency
  OFCH: Offset in channels
  DOVE: Use velocities given below for sky frequency recalculation
  DOFR: Use frequencies given below for sky frequency recalculation
  DOFV: Use both, the frequencies and the velocities given below.

• LEVELCONTR < contr > : automatic level control for quantization
  -1: level-control before every subscan
  0: no level-control at all
  +1: level-control before the beginning of a scan
• AC_OPTIONS < IF_conn > < quantization > < output_func > :

  < IF_conn > defines the connection of the analogue input channels to the four parts of the autocorrelator (ex.: 1234 or 2431).

  < quantization > defines the bit-quantization in the four possible channels (e.g. 2222 or 1111 or mixed 1221, where 1 = 1-bit quantization, and 2 = 2-bit quantization).

  < output_func > defines the type of function, which is archived (e.g. 3322 or 3333 or 2121):
  1: AC-function without clipping correction, (AC = autocorrelator)
  2: AC-function with clipping correction
  3: Spectrum

• CHANNELS_L < IF_distribution > : Sets the mode for the IF-distribution unit in front of the autocorrelator:
  0: Unit is not connected
  1: Receiver channel A to all AC-channels
  2: Receiver channel A to AC-channels 1 and 3, Receiver channel B to AC-channels 2 and 4
  3: Receiver channels A-D to AC channels A-D
  4: Internal noise generator to all AC channels
• PREINTEG_L < dump_time > : Sets integration-time < dump_time > in [millisec] for each data transfer to archive. The number of transfers per subscan depends upon the integration time, which is relevant for a subscan.
• BANDWIDTH_L < f1 > < f2 > < f3 > < f4 > [unit]:

  Bandwidth of the video input in GHz, MHz (default) or kHz. This can be any value from 50 MHz, reducing by factors of 2, to 48.8 kHz.

  NOTE : There is a special mode with 512 AC-channels and 100-MHz bandwidth using /SPLIT1

• FRQ_DOPPLER < o1 > < o2 > < o3 > < o4 > [unit]: Frequencies or frequency offsets for the autocorrelator-channels in [unit] of GHz, MHz (default) or kHz, center frequencies ( > 200 MHz) or frequency differences. The < doppler-mode > in /SPLIT determines the way in which the frequencies are used.
• VEL_DOPPLER < v1 > < v2 > < v3 > < v4 > [unit]: Velocities for the autocorrelator channels in [unit] of km/sec (default) or m/sec. The < doppler-mode > in /SPLIT determines if the velocities are used.

LINE

  

OBSE  >  		 LINE   < name  >    < frq  >  [  < unit  > ]   < band  > 
		/DEFAULT
		/CATALOG_L   < catalog_name  >  /MODE   < mode  > 

LINE allows the user to enter center frequencies from a line catalog directly into C_MODE, L_MODE or the FRQ_DOPPLER option in AUTOCORREL. If parameters are entered as current values, they remain active until the verb is entered again, except the /DEFAULT adverb is used to tranfer the parameters into the default values.

• < name >     the line name is mandatory !

  If the line name is the only parameter for the VERB, the line catalog is searched for the first entry which matches that name exactly. Then the frequency, and possibly the side band, is extracted and sent to the ADVERB selected via the /MODE.

  If additional parameters are entered for the VERB, it is assumed to be the direct input of the frequency with a possible unit, side-band and fix indicator. These values are sent as typed to the ADVERB selected by the /MODE.

  The line name of a line observation is transferred to the CLASS data reduction package. This holds for names entered with a MODE that sets FREQUENCY_L as well as names entered with MODE D(1..4), which are used for setting the synthesizers in the autocorrelator split modes. Always the last entry is used. If the split mode is used for different spectral lines, make sure that the frontend frequency (MODE L) is entered before the lines for the various split modes, otherwise the name of the frontend frequency is used, since it is the last line name.

ADVERBS:

• CATALOG_L allows you to declare a line-catalog name for just that call. Otherwise, the default catalog is scanned.
• MODE determines where the frequency input should go.

  If the current value of mode is starting with a letter other than L,C or D the input extracted goes to both, the line observing frequency FREQUENCY_L of L_MODE and the continuum observing frequency FREQUENCY_C of C_MODE. If you want to set them differently or use the input for the split in the correlator set the MODE adverb accordingly.

  < mode > = L : The frequency input goes to FREQUENCY_L of the line mode, L_MODE only.

  < mode > = C : The frequency input goes to FREQUENCY_C of the continuum mode, C_MODE only.

  < mode > = D1..D4: The frequency input goes to the FRQ_DOPPLER 1..4 of the autocorrelator's Doppler frequency offsets.

  EXAMPLES :

  LINE EFFELSBERG_2.8_CM/MODE CONT

  will extract the 10550 MHz from the line catalog and store it in FREQUENCY_C for continuum observations.

  LINE XXXX 5.006 USB

  will set the spectral-line center frequency almost to H109 $\alpha$ .

SOURCE

  

OBSE  >  		SOURCE   < name  >  
		/DEFAULT 		 /CATALOG_C   < cat_name  >  
		/VELOCITY   < vel  >    < frame  > 

From the catalog < cat_name > , this VERB selects information such as longitude and latitude, catalog epoch, and a velocity for spectral-line work for the source called < name > , The VELOCITY option can be used to overwrite the catalog information if a spectral line should be centered at a different velocity. If parameters are entered as current values, they remain active until the verb is entered again, except the /DEFAULT adverb is used to tranfer the parameters into the default values.

• < name >     the source name is mandatory !

  NOTE: the first entry that matches the characters typed is extracted, (more information about catalogs one finds in Section 4) Longitude, latitude and a position angle can be given in a variety of astronomical coordinate systems, and in general a standard epoch and catalog positions are used. When an object within the solar system is selected (the first three letters of its name are tested), the coordinate system is centered on that object, and its coordinates are (0,0). For more information see the OBSINP Manual.

ADVERBS:

• CATALOG_C < cat_name >

  If the option CATALOG_C is present, then the catalog with the name < cat_name > is used to find the source for just the present execution of the command SOURCE. At the next invocation of SOURCE, the default catalog is reverted to, or the option CATALOG_C has to be entered afresh (or recalled with the SIC edit arrows).

  Directories other than the current one have to be explicitly typed in if the catalog is in a different directory. However, do not type a device name containing a ":" , since OBSINP skips the remainder of the line after the colon.

  EXAMPLE:

  OBSE > SOURCE ALFORI/CATA [SCHRAML.ASTRO]STAR

  This will extract the epoch (1950) coordinates for Betelgeuse.

• VELOCITY < km/sec or zred > < velocity_frame >

  The velocity extracted from the catalog (should the catalog contain any) will be overwritten by the value specified. If /VEL is not present, such overwriting will not occur.

  The first parameter is the numerical value of a velocity. Units of KM or M can be given, with the default being km/sec.

  The second parameter specifies the velocity frame. The first, or first two, characters are tested. If this parameter is missing, the default value is used. For this parameter,

  H or VH = heliocentric,
  B or VB = barycentric,
  L or VL = LSR (i.e. with respect to the local standard of rest), and,
  Z = redshift, implying that the first parameter is the numerical redshift.

  EXAMPLE:

  
  OBSE  >  SET_DEFAULT VELOCITY * VBAR
  OBSE  >  SOURCE name/VEL 20 		will yield V(barycentric)   =  20 km/sec
  OBSE  >  SOURCE name/VEL 20 HEL 		will yield  V(heliocentric)   =  20 km/sec.
  

    NOTE: If you require a source not contained in any source catalog, you should use the OBSINP commands under OBS _E :

  OBSINP         (to enter the OBSINP-level)
  SNAM mySource
  SLAM ...
  SBET ...
  QUIT         (to leave the OBSINP-level again)
  

  (See the OBSINP-manual for more information !)