The GMRT : User`s Manual - Tata Institute of Fundamental Research
Contents
1. Proj SYS Observer SELF Title SYS TEST Tue Jun 11 17 10 33 2002 T130B175 Chan 44 1000 Normalised ccf Source 3C286 RF 1280 L01 1210 BBLO 70MHTime 17 17 19 46 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 47 18 19 20 2 22 23 24 D 26 27 28 29 coo Coil CO2 CO3 CO4 COS CO6 COS CO9 C10 C11 C12 C13 Cid E02 E03 E04 E05 E06 S01 S02 SO3 SO4 S06 WO1 WO2 WO3 WO4 WOS WO6 deem coo cot coz Los 04 COB C06 Cos cog C10 C11 C12 C13 C14 E02 E03 E04 E05 E06 S01 502 503 504 S06 NO NOZ NOZ Wod WoS NOG 1266 39 44 41 43 36 43 41 39 48 40 44 45 40 45 46 33 46 42 46 38 42 44 35 27 B 43 49 34 45 s 210 47 42 47 40 46 44 39 51 45 49 45 44 47 51 39 48 45 50 39 45 43 31 27 57 50 50 36 46 46 K 1266 44 51 241 52 47 45 55 49 51 50 46 50 54 4 57 47 48 48 50 52 37 31 58 55 54 44 50 37 42 E p 42 35 46 41 38 49 43 44 45 42 43 47 38 47 43 49 36 43 43 36 26 52 43 52 39 41 49 59 64 E 1083 41 49 48 44 53 45 50 51 48 50 52 39 SL 47 52 40 48 46 37 29 5B 51 52 41 49 39 46 49 40 a 1747 39 39 36 45 34 42 41 39 37 41 32 44 40 44 35 38 39 30 24 47 44 47 34 41 43 56 53 48 61 1433 1057 50 44 51 42. E06 57 S01 502 3 56 W Q BN oF Oe NW GM W B BB O m 03 62 S04 5 S06 oo Q O0 6 Ww BW P HN WN OG ON WY Be OHH BN UW NO NOZ 6 NOZ 20 2 620 xxx Hog 53 1619 1526 xxx NOS 46 5 1238 1604 HOG 4 1 45 Figure 3 An example of a few unhealthy antennas The sensitivity in the total power mode would be SR Tiotal power X A RATE and in interferometric mode would be k Toys T jue Sys Tinterterometric X 2 A A12 Av T Where Tsys amp Ty are repectively the system temperatures of the two antennas and A amp A are the corresponding effective areas of them 29
3. astro0 gt tax tax in rawdata 8jun O1TSTO1 1ta tax gt scans 0 1 2 31 dhanishtha Ondisp IDATE 1020ct15 TIME 23 7420 LST 00207 04 1 PACKET 1431508 USRO 149175 usero 5 LOAD NEW ANT SPECIFIC TRAK PARA ProgID 4 TRUE Nonnt Z 30 SLatez TRKG OUTTRK Source 3C48 ih34m49 83 32d54 20 5 Offs Target Az 230d00 16 6 El 65d49756 60 CoO Cot Coe Cos Co4 CO CoG CoS COS Cio Cii CZ Cis C14 E92 8d 22d 562 28d 39d 27d 33d 40d Zid 42d 22d 46d 35d Zid bo a SER T fae vei E gp M CRAT D eae di Z OtVF Z Z 2 Z Z Z z Z Z Z zB E05 0 4 3 MOB HOG 02 S03 04 Sob 977 4d 562 20d 5d 557 14d 66d 18d 24 66d 397 Figure 6 An example of the ondisp display tax object tax timestamps tax baselines Coo 20 tax gt channels tax gt antennas tax gt integtime tax gt normalize tax gt fmt tax gt go ist 10 5f base chanfaf11 4f p 8 1 n extracts the scans 0 1 2 of the 01TSTO1 Ita OR astro0 gt tax tax gt in rawdata 8jun O1TSTO1 1ta tax scans tax object 3C147 3C286 tax timestamps tax baselines coo 20 tax gt channels tax gt antennas tax gt integtime tax gt normalize tax gt fmt ist 10 5f base chanfaf11 4f p 8 1 3 n 32 tax gt go would extract all scans of the two sources 3C147 and 3C129 You can
4. Figure 11 Spectrum analyser output from optical fibre for a few of the antennas each plot showing 130 and 175 MHz S06 in left Figure shows spikes RFIs in both channels 6 3 Primary Beam Gain Correction Coefficients to use in the task PBCOR in AIPS for primary beam correction of GMRT data are tabulated here The polynomial fit to the beam is 1 a 10 2 b 107 a c 10 0 x d 1013 z5 where where x is in terms of separation from pointing position in arcmin frequency in GHz a b c d are the coefficients which are required to be specified in PBCOR when using GMRT data PBPARM 3 a PBPARM 4 b PBPARM 5 c PBPARM 6 d PBPARM 7 0 for GMRT More information can be found at http www ncra tifr res in ngk primarybeam beam html 610 MHz 3 486 47 749 35 203 10 399 44 4 2 27961 21 4611 9 7929 1 80153 26 2 1280 MHz Table 10 Primary Beam Gain Correction 6 3 4 Running AIPS on your data If you are combining data from both the sidebands first run 1tamerge to create com bined datafile using the following commands astrol gt ltamerge i InputLtbFile I InputLtaFile 40 This would create file ltamerge_out 1ta Then run gvfits it provides UV data in J2000 epoch to use gvfits you first need to run the program listscan to create log and plan files Edit the log file to select normalization type a subset of the data etc Finally run gvfits on the edited log file e g ast
5. 175 MHz 130 MHz 175 MHz 130 MHz 175 MHz 130 MHz 175 MHz BASEBAND PARAMETERS set para 16 onwards Select the antenna group O if all ant bb mentioned below 16000 8000 4000 2000 1000 500 250 125 62 cof 3 23 6 9 12 15 18 21 24 Select BBLO Hz Synth 1 Freq MHz 50 0 lt LO lt 90 0 step 100Hz 66 0000 Select BBLO Hz Synth 2 Freq MHz 50 0 lt LO lt 90 0 step 100Hz 66 0000 Select Map for BB LO Synthesizer Chan 1 Chan 2 1 Synth 1 Synth 1 2 Synth 2 Synth 2 3 Synth 1 Synth 2 4 Synth 2 Synth 1 3 Now run gt setdlo gt setdif gt setdrf etc tpa to be given is 614 244 680 310 66 66 Record 64 channels needs to be mentioned in corrsys hdr file and look at the band shape from the showband tcl programme 0 63 1 Check with MATMON and also check DASSTAT window After the observation you can convert your data in FITS using gufits Use the gvfits programme as follows astrol gt listscan rawdata 7jun 01TSTO1_OBJ 1ta astroil vi O1TST01_0BJ log astroi gt gvfits O1TSTO1 0BJ log For examples editing O1TSTO1 0BJ 1og suggests to keep one of the stokes say RR also important is to choose normalisation unnormalisation The output TEST FITS would correspond to one of the frequency data 614 MHz and re run gvfits for the other stokes i e LL 240 MHz data 4 4 Default parameters The def
6. temp2 data source 01TST1 list addlist temp2 data source 01TSTl list Inkndas suba 4 goin gosacin cp 0 gts 0237 23 sndsacsrc l lh time 0 5m sndsacsrc l lh stabct strtndasc time 10 0m stpndasc gts 0213 132 sndsacsrc l lh time 1 5m sndsacsrc l lh stabct strtndasc time 10 0m stpndasc gts 0235 19 sndsacsrc l lh time 1 0m sndsacsrc l lh stabct strtndasc time 10 0m stpndasc gts 0240 00 sndsacsrc l lh time 1 0m sndsacsrc l lh stabct strtndasc time 10 0m stpndasc gts 0349 27 sndsacsrc l lh time 1 0m sndsacsrc l lh time 1 0m sndsacsrc l lh stabct strtndasc time 10 0m stpndasc gts 0403 13 sndsacsrc l lh time 1 0m sndsacsrc l lh stabct strtndasc time 10 0m stpndasc gts 0442 28 sndsacsrc l lh time 1 0m sndsacsrc l lh stabct strtndasc time 10 0m stpndasc end cmode 1 addlist temp2 data source 01TST1 list Inkndas suba 4 goout gosacout cp 0 gts 3C286 sndsacsrc l lh time 0 2m sndsacsrc 1l lh stabct strtndasc time 10 0m stpndasc gts 1323 32 sndsacsrc 1 1h time 1 0m sndsacsrc 1 1h stabct strtndasc time 10 0m stpndasc gts 1328 25 sndsacsrc 1l lh time 1 0m sndsacsrc 1l lh stabct strtndasc time 10 0m stpndasc gts 1350 31 sndsacsrc 1l l1h time 1 0m sndsacsrc 1l lh stabct strtndasc time 10 0m stpndasc gts 3C286 sndsacsrc 1 1h time 1 0m sndsacsrc 1 1h stabct strtndasc time 10 0m stpnd
7. across the band What differentiates spectral line observations from standard contin uum observations is that the local oscillator settings are important so as not to miss the spectral line which is expected at a certain frequency For the continuum observations one can use the default settings see Table 9 for the desired band Moreover one can choose to record less than 128 channels in the case of continuum observations whereas for spectral line projects recording data of all channels would be desirable For spectral line projects the user will need to have an idea of the observing frequency and the desired bandwidths 1 Determining the observing frequency Once you know the rest frequency of your spectral line the redshift for far Universe objects should give you the observing frequency In case of Galactic or near Universe objects the NRAO programme dopset available via usual source astro RC can be used to obtain the change in the rest frequency due to the earth s rotation and motion around the Sun so as to obtain the heliocentric or the local standard of rest values Please note that online Doppler correction is not provided at GMRT the change over an eight hour run is 1 km s 2 Determining the baseband bandwidth The available bandwidths at GMRT are in binary steps from 62 kHz to 16 MHz Observations with bandwidths greater than 0 5 MHz are regularly made whereas the lower bandwidths are not frequently used You will
8. 1 Freq MHz 50 0 LO 90 0 step 100 Hz 70 0000 Select BB LO Hz Synth 2 Freq MHz 50 0 LO 90 0 step 100 Hz 70 0000 Select Map for BB LO Synthesizer Chan 1 Chan 2 Synth 1 Synth 1 e Synth 2 Synth 2 Synth 1 Synth 2 2 Synth 2 Synth 1 7 L N KA and run corresponding program which creates the control word ONLINE has five different user control for general purpose named userl user2 user3 user4 and user5 For example observer having control of user4 should use cdset4 It creates control words for RF LO IF and BB in separate files which have to be sent to the antennas and baseband systems using the following commands gt run set4rf This will set the front end parameter according to the modification in setupnew txt file If you use cdset1 to edit the parameter file then above command would be run setirf The same thing is applicable to setting LO and IF To set LO and IF use the following commands gt run set4lo gt run set4if Setting the baseband is quiet different from setting antenna s RF LO or IF as the baseband system itself is an ABC inside CEB We have to define a different subarray for baseband ABC conventionally called ABC 0 or CEB ABC having its ABC ID 0 This subarray will be running all the time on ONLINE server machine and conven tionally will be subarrayl SAC1 So to change the baseband setting you have to give commands to
9. PC and GPS time d ionospheric variations The winding will be random 3 Fstop window says link reset packet transmission not possible a fstop has crashed 4 Some baselines record low cross correlation on a point source a Is polarisation swap required on some antennas applied a b Are the self correlations of problem antennas as expected c d stpdasc gts srcname strtdasc Are pointing offsets being loaded 5 The LTA and AIPS file header shows RF 0 Hz IF_LO 0 Hz BB LO 0 Hz a If noticed during observations stpdasc and stpdass and start again Don t forget to set TPARM Frequency parameters to correlator b If noticed after observations forget about that data and get a fresh run 49
10. and 4 1 for more information gt prjfreq Copy project parameters into ONLINE shared memory gt I1nkndas Setup the link between ONLINE and DAS gts srcname Get source parameters gt sndsacsrc 1 12h Position antennas to the source and begin tracking gt strtndas Start the data acquisition for the given source gt stpndas Stop the data acquisition for the given source gt opsacfil odisk gtac cmd yourname cmd To open the Sacfile or Command file gt strtsacfil It gives control to the subarray controller which reads the instructions from above mentioned file yourname cmd gt stpsacfil Stop the command file yourname cmd e From UserO window of online gt cmode 3 1 for USB 2 for LSB 3 for both gt suba 4 subarray number for which project is to be started gt stpprj Stop the project hltndas Halts acquiring the data from correlator 13 Part II Before observing 4 Preparing for Observations The following should be carried out before the observing session for ALL OBSERVA TIONS 1 Check GMRT specifications to choose the appropriate frequency primary and synthesized beam sizes to match the source and the science Parabolic Reflector Diameter Focal Length Physical aperture Sensitivity of single dish Feed Support Mounting Elevation Limits Azimuth Limits Slew rate Design wind speeds 3 sec peak at 10 m height Size of wire mesh of reflecting surface Maximum rms surface errors at wind s
11. are given in Table 4 It is advis able to use the narrowest IF bandwidth possible so as avoid RFI corrupting the data For an observing run of 9 hours with all 30 antennas and 128 channels in the USB you will end up with a filesize of gt 2 GB The data backup facility at GMRT Section 6 4 includes several 4mm dat tape drives for 24 GB dat tapes 21 4 2 Bypass mode of 1420 MHz A bypass mode is available for the L band so that the entire 500 MHz bandwidth can be accessed This mode allows one to access frequencies ranging from 850 MHz to 1500 MHz and without choosing each sub bands each sub band is centred at 1060 1170 1280 and 1390 MHz with a bandwidth of 120 MHz It is generally advised that while accessing the higher end of the frequency you set the LO1 gt RF and for the lower frequency end set LO4 lt RF This prevents the image band corrupting your band of interest Although this allows you to use cover a larger bandwidth it may corrupt your data from local radio frequency interference 4 3 Dual frequency observations You also may want to observe simultaneously at two frequencies This is possible only at 233 and 610 MHz frequencies You would need to edit the SETUPNEW TXT file as follows instead one can just say cdsetd on the unix prompt here onwards all settings for the first channel is for 610 and second channel is for 235 MHz band Watch on the settings like attenuator LO IF etc for these two channels t
12. for the narrow bandwidths used For the distant Universe these settings are more coarse since the bandwidths generally employed are large To help you with these settings a locally developed programme tune is available at GMRT The programme is user friendly and will help you play around with the local oscillator frequencies both for LO1 gt RF and LO1 RF Default settings are as follows 150 MHz LO1 gt RF 240 MHz LO1 gt RF 330 MHz LO1 lt RF 610 MHz LO1 lt RF L sub bands L01 lt RF and visualize your observing band It also provides you with default local oscil lator settings for each GMRT frequency band used for continuum observations Please note that LOI the first local oscillator in electronics has a least count of 1 MHz for frequencies 350 MHz and a least count of 5 MHz for frequencies gt 350 MHz This translates practically to the fact that only coarse settings are possible in the LO1 whereas the fine settings have to be implemented using LO4 the fourth LO in the electronics Only LO1 and LO4 are under user control since LO2 and LO3 are used for optical fibre transmission from the antennas base to the receiver room Once you have determined all the required frequencies you can use the Frequency Setting Calculator on the GMRT web page to deter mine the array of parameters tpa which are required by the correlator The TPA array consists of 6 members namely as follows RF freq in spec chan 1 for 130 MHz RF freq in
13. put it in shared memory Anyone can attach to that shared memory and get the data to display it according to his her convenience and to record on disk e INTRODUCTION A number of new correlator data acquisition modes are now available for test These modes include 1 Full stokes in either USB or LSB 2 256 channels in RR and LL in either USB or LSB for all baseband bandwidths 16 MHZ or smaller 3 identical data being piped through both halves of the correlator either for pos sible SNR improvements as routinely used elsewhere or for testing 4 In addition of course the old Indian Polar mode continues to be supported There has also been a substantial change in the way in which users initialize and reconfigure the correlator and das software Rather than having to consistently edit several text files on several different PCs and supply consistent command line options users now run a single program that guides them through a menu This program runs on the ONLINE machine shivneri lenyadri and produces a parameter file temp2 data corrsel hdr Wrappers running on shivneri lenyadri read this file and will initialize reconfigure the correlator as appropriate for the selected observing mode Information required for configuring acq30 dlytrk etc is also taken from this same file and transferred to appropriate locations by dassrv This entire operation of transfer of parameters is transparent to the user Step by step i
14. spec chan 1 for 175 MHz LOL for 130 MHz LO for175 MHz LO 4f0r130 MHz LO4for175 MHz where 130 MHz corresponds to RR and 175 MHz to LL polarisations Please note that RFfeq LO1 LO4 If you plan on dual frequency observations ie 240 MHz on LL and 610 MHz on RR default you will follow the explana tion discussed just above In addition to the above depending on your base band bandwidth you will need to tell the correlator the sampling frequency A 20 parameter named CLK SEL is required to be specified for this purpose The Frequency Setting Calulator avaliable on GMRT web page will tell you the required CLK SEL once you have specified the baseband bandwidth You can also calculate it yourself as 9CLK SEL _ 16 baseband BW So if your baseband width is 8 MHz then CLK_SEL 1 see Table 4 An example will make the above easier to comprehend Suppose we have proposed and have been alloted time for making a Galactic HI absorption measurement using GMRT The rest frequency of the HI line is 1420 40575 MHz Assume that the velocity cor rection due to the earth Sun motion and the source velocity computed using dopset shifts the line to a frequency of 1420 505 MHz We would like to center our band on this frequency The expected width of the HI line is 10 km s translating to about 48 kHz at 1400 MHz So we would desire a channel width of about 48 4 12 kHz For a channel width of 12 kHz the total bandwidth you can observe
15. subarray no 0 The baseband is having 16 MCMs each controlling the one polarisation and its both sidebands for four antennas If we send proper control word to MCM it switches the band width and the gain according to selection Use the following command to set baseband bandwidth gain and ALC status gt stbbfile 130 default gain files 130 csv gt stbbfile 175 default gain files 175 csv gt stbbalc both both 1 stbbalc 130 175 both usb Isb both 1 0 gt stbbwgnall 16000 0 stbbwgnall bandwidth gain gt stbblo 70 0000 70 0000 stbblo 1o4 1 104 2 These commands should be run in USERO 3 1 2 Running up correlator for recording astronomical data Based on a note by Dr Jayaram Chengalur Correlator has it s own control software which also talks to ONLINE software over computer network Few programs have to be run from corrletor control computer in beginning of observation session Then onwards control goes to ONLINE software Only a few commands it takes to change the source start das stop das and stop the whole observing session For data acquisition there are two more computers involved mithuna For USB amp mithunb For LSB which talks to correlator control PCs corracqa For USB corracqb For LSB and corrctl For delay traking and fringe stopping over the network It creates a shared memory in it and takes the data from correlator control PC
16. 0 58 48 2263 aao 38 25 857 53 46 41 48 32 40 43 34 44 35 41 27 41 41 42 40 41 41 39 21 34 42 42 46 37 41 ui 1575 19 44 36 42 34 37 47 57 58 46 62 48 60 36 58 54 58 54 51 49 53 27 46 58 51 59 52 56 56 s uy 35 32 32 22 33 49 62 63 53 66 55 65 di 61 59 59 60 56 SF 66 27 48 64 59 64 53 61 62 45 E 772 63 60 52 61 44 54 59 45 60 51 57 39 56 55 57 54 50 56 53 26 48 60 55 58 52 57 55 43 56 7 1246 57 44 55 42 50 55 41 59 50 54 34 53 54 55 54 51 53 53 25 d 57 53 61 45 56 51 42 56 62 a 1093 45 53 40 46 49 40 53 43 50 35 51 48 50 4 44 47 47 25 42 49 50 54 42 477 45 38 51 56 49 E 1250 42 37 45 51 32 47 38 46 34 44 43 48 44 41 42 44 22 41 50 44 47 41 46 45 32 49 51 49 44 E 1226 Figure 4 An example of all healthy antenna Cross correlation functions displayed on the dasmon Figures 2 3 and 4 are given by San Jy X K E Toys with some scaling factor usually 1000 Gol x where K is sensitivity and is in K Jy Each Figure shows the following i the diagonal elements are the self correlation coefficients ii the upper half elements are the 130 MHz channel cross correlation coefficients and iii the lower half elements are the 175 MHz channel cross correlation coefficients Explanations for a few examples of dasmon outputs is given below a Figure 2 Antennas C02 C05 C13 E01 S01 S05 and W04 were not avali able for observations see empty rows and columns corresponding to these antennas in the Figure 2 The observations were mad
17. 5 52 51 46 46 51 40 53 49 52 46 49 50 37 28 64 53 53 44 53 28 39 40 30 36 32 US 1247 45 51 47 48 49 44 50 50 38 57 49 54 39 47 48 35 30 56 50 50 40 49 43 54 57 44 60 46 54 a 45 39 45 45 43 44 46 37 46 43 46 38 46 45 34 27 51 50 47 42 43 42 52 57 46 61 48 56 37 155 1124 47 54 55 51 52 55 45 56 53 59 45 52 51 38 33 64 59 57 46 53 44 56 60 47 61 50 58 39 54 S 1391 50 49 46 46 49 39 50 44 48 42 44 49 37 28 56 49 50 42 45 44 50 55 43 57 49 54 36 49 50 S Toce 51 49 49 56 41 52 50 58 46 50 49 39 30 62 52 56 45 46 41 50 55 39 53 42 52 33 47 49 50 E 1085 50 51 54 41 58 50 54 46 49 47 39 27 61 SF 55 41 49 43 52 5 43 BE 47 50 3 50 52 55 5i 1275 1163 48 50 37 52 47 50 41 48 47 37 28 54 51 SL 40 48 41 53 56 43 60 47 56 35 51 52 54 51 50 E 5255 49 37 54 50 51 40 47 251 38 30 56 51 54 44 45 21 25 2 19 29 24 30 18 24 24 27 27 24 26 E 1305 42 59 56 54 42 50 47 40 33 63 56 56 46 52 35 44 49 35 49 40 47 30 46 48 43 43 42 44 44 En 656 48 42 42 37 40 39 32 21 48 43 46 34 41 48 60 63 48 63 48 60 39 59 57 61 59 52 54 57 27 E tise 58 57 47 50 54 dO 31 64 57 60 46 54 39 50 54 40 57 47 51 33 54 53 50 49 46 48 49 25 497 NZ 1240 52 44 50 44 38 29 58 49 54 43 48 48 60 61 51 65 54 61 39 59 62 61 59 SB 57 57 27 46 G1 Er oos 46 53 149 37 29 62 55 57 46 50 38 48 49 35 56 43 53 32 45 47 51 46 44 46 46 25 41 51 44 12 e 44 45 33 27 50 47 47 37 44 4 54 55 43 E58 47 57 39 53 54 56 52 47 53 51 28 44 58 55 60 E 1191 51 41 32 56 52 50 40 48 41 52 59 42 59 49 54 34 55 51 56 51 47 52 53 25 43 60 5
18. EP acq RUNNING AND JUST CHECK FOR SYNCHRONIZATION PROB LEMS AFTER YOU RESTART IF THINGS ARE SYNCHRONIZED THEN FINE OTHERWISE YOU WILL NEED TO KILL AND RESTART acq start acq acq30 sockemd fstop dlytrk dassrv collect on the appropriate ma chines Note that none of the programs need command line options but instead as explained in the introduction will automatically understand the selected ob serving mode NB The acqs on corracqa corracqb corrctl should be started within 1 STA cy cle i e 128 ms of each other The easiest way to do this is 10 Mode Name Band Mask IndianPolar UsbPolar LsbPolar UsbHighRes LsbHighRes UsbCopy LsbCopy AlIU130 AIIU175 AIIL130 AIIL175 Table 3 Bandmask for Each Mode a export the corracqa b ctl window to all desktops b go to any one desktop and align the acq windows one below the other c type acq in all windows but don t type ENTER d hit the ENTER button in all windows in quick succession I agree that this is a pretty silly way to do things A more automatic method is in the prorverbial pipeline Ask the operator to give an init and add a project from the master terminal The bandmask while initing and adding a project should be correspond to the chosen mode NB The bandmask is a bit mask with bits in the order USB130 USB 175 LSB130 LSB175 For a pure USB observation the bandmask is 3 e g UsbPolar UsbCopy All1U130 For a pure LSB observation th
19. Hz so that they can be brought to the receiver room on the same optical fibre The 3rd LO in the receiver room is used to bring the two polarisations back to 70 MHz in the local jargon the two channels are also referred to as the 130 and 175 MHz signal These two channels are also termed as the RR and LL Stokes parameters respectively Two sidebands USB amp LSB are available This makes two IFs and each of the IFs having two channels 130 and 175 MHz or Stokes The 1st LO and the 4th LO should be specified both for the spectral line and the continuum observations depending on the observer s requirements The 1st LO can be set in steps of 1 MHz for frequencies from 150 to 354 MHz and in steps of 5 MHz for frequencies from 350 to 1795 MHz GMRT sub systems report The 4th LO which converts the IF signal to the baseband sometime written as BB can be set with in steps of 100 Hz over the range 50 MHz to 90 MHz Both the 1st LO and the 4th LO can be set via software At the antenna base after the IF conversion an automatic level control ALC system is available This adjusts for the varying signal levels at the output of the IF and is controlled by the software After the baseband conversion each of the two IFs is split into two bands the upper and the lower sideband Here again an ALC system is available e at the output of the baseband converter which adjusts for varying signal levels For interferometric observations the ALCs are
20. RT ee Ses 42 Computer Facilities at the NCRA ep ehe d 43 List of Tables SWS ON O G WwW NH 10 ITU specified Protected frequency bands sss 2 Correlator Modes ue uS ROS X Gye Se des xe UA 10 Bandmask for Each Mode oss ee Soe Pe Se REESE SUD eA 11 Bandwidth CLK SEL and IF selection 12 The GMRT specifications 2 0 0 20020 15 HeeddeScriptl0h s sissa eis e R E een Bee ty es we edt Qt TR oh dut the tene dee 16 Measured System Parameters of GMRT 16 Table showing IF baseband bandwidths and polarisation swap 17 Default settings used for continuum observations for the GMRT fre quency DABIS ore ms od deste E aie here in ander e ee ot eie enu edo Ree 25 Primary Beam Gain Correction een 40 List of Figures N on 4 wnwe 10 The block diagram of the reciever system a a a 3 An example of many unhealthy antennas 28 An example of a few unhealthy antennas 29 An example of all healthy antenna ll 30 An example of the mon tcl display lll 31 An example of the ondisp display llle 32 Stokes RR bandshapes of C01 amp E05 and W01 amp W05 33 Stokes LL bandshapes of C03 amp C05 E02 amp W06 and S04 in S04 ltaflag programme has removed the spikes ls 34 Amplitude and phases of Primary first and secondary l
21. S03 USB4 30 C09 J E C a ibis o a AE J 60 4 ES j E mm j eu E x S03 USB 130 C09 E ABE j oors E J otes S ami d voli X Nd x J 150 L x R x a X RRE x E 4 100 menr erer S02 USB 130 C09 X J L J 100 H x x 4 cows 4 0 04 H poem UI ee m S S02 USB 130 C09 j 0 025 saat 0 02 K B L E dy p my iie 1 a zs ES 23 5 A EA as cni aE EI J wF P ow oai W06 USB 130 C09 oH o 4 e e 1 d 200 BP 0 035 opo Sarap W06 USB 130 C09 0 02 H al 0 015 K zl 0 01 K ZA 0 005 od Wip B lb PT J 200 LI iso L Omo o n o o mr gl oF o z wE En RU dP Po Bp a 2 WOS USEis 30 CO9 er J 50 H R ao BH a o oe of o at o G or ug gH B 4 nog q A s F oO 4 50 D o el ZL ow De y NA 5 x 7 dena L Hes H g Cents H ac gH o d T 5 RC Soc deu s ce E W05 USB 130 C09 J 0 0015 a 3 X E Eos Xx em a x x Te 4 0 001 Ta x RE z xx N x XX x at 7 ep KVA E SA AMEN BEES E 200 x E 150 i x K x E oni T T W03 USB 130 C09 2E MEME e 7 E L T T T T x T i E 05 H P es Taparia 4 sal W03 USB 130 C09 7 0 03 K zl 0 02 L oor agr U dm che cape W gt 0 Figure 10 Amplitude and phases of Primary first scan and secondary later scans cali brators 3C286 1351 018 respectively on baselines S02 S03 amp S06 upper and W03 W05 amp W06 lower C09 being the reference antenna amplitude is in arbitrary units 36 37 Part IV After Observing 6 Your data Data collec
22. The GMRT User s Manual The GMRT User s Manual Dharam Vir Lal A Pramesh Rao Manisha S Jangam Nimisha G Kantharia Contents I Overview of the GMRT 1 The Array ll Protected frequency bands 444 5424 6844 4854 4 4003 2 The Receiver System 3 GMRT system 3 1 The Control Systemi S uem ede wander eem Ee aos 31 1 Setting RF LO IF and BD 1 3 1 2 Running up correlator for recording astronomical data II Before observing 4 Preparing for Observations 4 1 Spectral line observing with GMRT 42 Bypass mode of 1420 MHz ete ere poma De eo ee ew Reb OG 4 3 Dual frequency observations lt 4 402 m Ou he ee ERS 4 4 Default parameters 24 424 2 SA RD SAS ee es III While Observing 5 During the Observations 5 1 Inputs to the operator in the GMRT Control Room 52 Data quality and monitoring ooa a 5 2 1 Total Power cuc dow a uuum inui WIE IV After Observing 6 Your data 6 1 Interference Monitoring aaa aa d adie a ute amp nen GA 6 2 Running AIPS at the GMRT 4 a rubo Po Dak YID 6 3 Primary Beam Gain Correction 0 0 0 0 0 ou A PB 14 15 19 22 22 24 25 26 26 27 28 38 6 4 6 5 6 6 6 7 63 1 Running AIPS on your data hr rer UE ache ede e 40 Backine your DATA Co wu ede dite Wide amp a diate E 28 naar R a P 41 Your observation log aut deri bus Qr Eun eer end S e 41 Computer Facilities at the GM
23. The monitoring needed for continuum observations are largely given by the dasmon dasmon is a snapshot mode of getting a quick health check of the 28 system at a particular time Following Figures 2 3 and 4 gives examples of available healthy and poor antennas Proj O1TOIO2 Observer ISHWAR Title Fri Jun 7 09 16 50 2002 T130B175 Chan 40 1000 Normalised ccf Source 3C0147 RF 614 LO1 680 BBLO 66MHz Time 33 23 11 01 10 11 19 20 0 1 2 3 4 5 6 E 8 9 15 16 17 2j Gol RS 26 27 COO COL CO2 CO3 CO4 COS CO6 COB CO9 C10 Cii C12 E03 E04 E05 S01 S02 03 S04 S06 HOZ M4 sine Co0884 87 91 74 2 93 93 78 92 87 391 Bt 88 B77 xxx COi 42 1054 2 118 123 100 117 832 coz 47 87 3 127 125 104 32 3 76 90 47 95 D 39 59 ES 49 62 co3 32 79 2 103 104 94 ves coa 4 11 711 i 4 1245 C05 di 94 11 C06 35 95 7 coe 7 16 5 toS 38 93 11 41 2 53 1 50 55 62 70 37 55 56 62 Cio 48 96 5 56 64 C11 51 C12 34 53 60 55 41 C13 44 Cid 34 45 41 66 51 VI 0 H H N H N WW K N WW B w OU E02 54 E03 48 60 64 E04 3 2 33 E05
24. Visitor Feedback Form avail able at GMRT home page All publications resulting from the GMRT data should have an acknowledgement of the form We thank the staff of the GMRT who have made these observations possible GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research 44 Appendix Z2 The input files The source file The following is the source file specific example can be picked from odisk gtac source yourname list 3C286 13h28m49 66s 30d45 58 7 1950 0 1637 626 16h37m55 31s 62d40 34 3 1950 0 N6503 00h40m19 70s 51d47 07 2 1950 0 IS01 15h36m00 00s 50d00 00 0 2000 0 NGC1097 02h46m19 0s 30d416 28 0 1950 0 The command file The following is a simple command file The consecutive num bers are NOT in the file itself but are used for the explanation given here The file observes a flux density calibrator 3C286 for 30 minutes first then a phase calibrator 1637 626 and then enters a loop in which the phase calibrator and the source N6503 are observed consecutively and continuously with 10 minutes on the phase calibrator and 30 minutes on source In most cases the first part of the observing session will not be run from this file but by issuing commands from the monitor at least until the user is satisfied that both the flux density calibrator and the first part of a run on the phase calibrator are satisfactory Running manually also allows the user to bette
25. also choose the full band from 880 to 1450 MHZ this is called as the bypass mode of 1420 band see Section 4 2 for more details A block diagram of the receiver system Figure 1 is shown below RF signals are CHi OUT CTOR a POST AMP u RF CABLE PHASE SWITCH BAND SELE tr o o W ul o a X d SI i n E E L uj 3 z ii di lt e m T 1 0j D S Z POST AMP prp PHASE so 502504275 MHZ SWITCH CRLONE SWITCHED BPFs RF CABLE COMMON BOX MULTIFREQUENCY RF FRONT ENDS FOR GMRT Figure 1 The block diagram of the reciever system received in two polarisations called CH1 and CH2 For all frequencies except the 1420 MHz band right and left circularly polarised signals are received whereas for the 1420 MHz band the signals are linearly polarised The intermediate frequency IF is 70 MHz with a maximum bandwidth 32 MHz The user can set IF bandwidth to 6 MBz 16 MHz and 32 MHz see Table 2 There are four local oscillators LOs the 1st and 4th LOs being under the control of the user The 2nd LO is at the antenna base and third is in the receiver room The 2nd LO changes the frequency to an intermediate value in order to transmit the signal 3 down the optical fibres into the central electronics building and the 3rd LO converts the signal back to the IF again The 2nd LO at the antenna base is used to shift the IFs of the two polarisations to 130 and 175 M
26. also run explain and know more about it s usage For example tax can also display your data bandpasses scans etc from 01TSTO1 Ita file Some of tax outputs are shown in the following Figures For example Figure 7 Stokes RR bandshapes of C01 amp E05 and W01 amp W05 Figure 8 Stokes LL bandshapes of C03 amp C05 E02 amp W06 and S04 Figure 9 Amplitude and phases of Primary first scan and secondary later scans calibrators 3C286 1351 018 respectively on baselines C00 amp C01 and E02 E03 amp W06 Figure 10 Amplitude and phases of Primary first scan and secondary later scans calibrators 3C286 1351 018 respectively on baselines S02 S03 amp S06 and W03 W05 amp W06 Figure 7 Stokes RR bandshapes of C01 amp E05 top two and W01 amp W05 bottom two the spikes seen is an effect of RFIs 33 li lt g P fil y zL L l J E I IMA I Mop J wi x c a Mi 7 i T f al C os T f Wy E S M f I A N V f LA To mi N L A B A b v py L M h N E P A i AJ j E HN Wn hy y iol y he M pue 7 Wo y Vi V y ba v d ho LA ne LAI V Figure 8 Stokes LL bandshapes of C03 amp C05 top two E02 amp W06 middle two and S04 b
27. ary and synthesized beam sizes and Ti among other parameters are also provided The elevation limit of the array has currently been set to 17 90 degrees software limit giving a declination range coverage from 53 to 90 degrees The telescope was planned to operate at 6 frequencies but it functions at 5 frequencies 151 MHz 235 MHz 325 MHz 610 MHz and 1000 1420 MHz There are 4 feed systems of which one 235 610 is a dual frequency feed Table 1 1 1 Protected frequency bands The frequency bands shown in Table 1 are protected that fall within GMRT observing bands Freq band 150 05 153 ITU 230 235 Indian 322 328 6 ITU 608 614 ITU 1400 1427 ITU Table 1 International Telecommunications Union specified Protected frequency bands 2 The Receiver System The GMRT receivers are designed to operate at 5 frequency bands 150 233 327 610 and 1420 MHz the 6th 50 MHz feed is yet to be implemented The half power radio frequency RF bandwidth sometimes written as BW for 150 235 325 and 610 MHz respectively is 40 40 60 and 100 MHz The 1420 MHz band is split into 4 sub bands centred at 1060 1170 1280 and 1390 MHz each with a bandwidth of 120 MHz Thus the bands overlap by 10 MHz and provide continuous frequency coverage from 1000 MHz to 1450 MHz This allows observations of HI from local gas to a redshift of about 0 4 Higher redshift HI can of course be detected in the lower frequency bands The user can
28. asc end 48 cmode 1 lnkndas subar 4 goout gosacout addlist temp2 data source vlacal list addlist temp2 data source 01TST1 list 1 gts 21394143 sndsacsrc 1 1h time 0 5m sndsacsrc 1 1h stabct strtndasc time 5 0m stpndasc gts 2232H17 sndsacsrc 1 1h time 0 5m sndsacsrc 1 1h stabct strtndasc time 5 0m stpndasc gts 3C433 sndsacsrc 1 1h time 0 5m sndsacsrc 1 1h stabct strtndasc time 8m hold stabct time 8m hold stabct time 8m hold stabct time 8m stpndasc goto 1 end cmode 1 dellist 2 addlist temp2 data source 01TSTl list lnkndasq subar 4 goout gosacout 1 stpsactrk gts 1035 564 sndsacsrc 1 1h time 1m sndsacsrc 1 1h stabct strtndasc time 10m stpndasc stpsactrk gts 1116 517 sndsacsrc 1 1h time 1m sndsacsrc 1 1h stabct strtndasc time 10m hold stabct time 10m hold stabct time 10m hold stabct stpndasc goto 1 end Appendix Z3 The trouble shooting The trouble shooting 1 Fringes Disappeared stpdasc gts srcname strtdasc are antennas tracking your source have they hit the azimuth limit c is your source extended has any of correlator software crashed have the front end parameters got reset ask the observer 2 Fringes are winding a check LO 1 and LO 4 settings b stpdasc tparm prjfreq gts srcname strtndas c check time synchronisation between correlator PCs and ONLINE
29. ata are collected with apparently functioning equipment The observer is responsible for the ultimate quality of the data its calibration and so on The displays say for USB that have proved useful so far to review the recent history of system temperature gain and total power level A few of these are outlined below 27 5 2 1 Total Power Proj _02TST02 Observer SAK MSU Title SUN OBSERVATION Sun Mar 31 12 09 38 2002 T130B175 Chan 44 1000 Normalised ccf Source 3C468 1 RF 1060 LO1 990 BBLO 7OMHzTime 12 11713 69 3 8 20 21 23 1 4 6 Z 8 3 10 311 15 16 17 1 CO tos Cod COS coe CO9 C10 C11 C12 E03 E04 E05 E06 02 03 S06 dee 149 11 20 24 23 me 6453 18 7091 wx 26 2391 6341 Figure 2 An example of many unhealthy antennas The values along the diagonal show the values of the self correlation coefficients the upper trangular half show the cross correlation coefficients for the 130 MHz channel and lower trangular half show the cross correlation coefficients for the 175 MHz channel The total power or system temperature when ALC is off is the single most important diagnostic of the status of the observations It contains information on everything from elevation to interference to the weather Display of total receiver power or system temperature is useful for all types of observing Several software are available to examine the data in the lta format Some of them are discussed below 1 dasmon
30. ater calibra tors on baselines with C09 reference and C00 C01 E02 E03 amp W06 35 Amplitude and phases of Primary first and secondary later calibra tors on baselines with C09 and 802 S03 S06 W03 W05 amp W06 36 11 Spectrum analyser output from optical fibre for a few of the antennas each plot showing 130 and 175 MHz S06 in left Figure shows spikes RFIs in LL both lt channelsr 2 eR oh ge are gee ooo mi Pop 21 Part I Overview of the GMRT 1 The Array The GMRT consists of 30 45 m diameter parabolic dishes spread over 25 km near the village of Khodad about 80 km north of Pune India The site coordinates are latitude 19 deg 05 min 48 sec North longitude 74 deg 03 min 00 sec East altitude 588 m The array consists of two main parts a central array of 14 antennas which are labelled C e g C00 C01 C14 and an outer Y consisting of 14 km long East West and South arms labelled E W and S respectively There are 5 antennas on each of the east and south arms and 6 antennas on the west arm Note that the numbering scheme is historical and is not consecutive also please note that there is no C07 E01 and S05 antennas dropped due to the shortage of funds For an overview of the GMRT telescope parameters etc please see http www ncra tifr res in http www gmrt ncra tifr res in and Section 4 It also gives details of the antenna feed specifications available fre quencies prim
31. ault settings used for continuum observations for the GMRT frequency bands in terms of RF LO1 LO4 frequency settings Solar Attn in dB and IF BB bandwidths all in MHz ALC Status are shown in the Table 9 24 Table 9 Default settings used for continuum observations for the GMRT frequency Freq Solar band Attn 150 14 235 14 325 0 610 0 1060 0 1170 0 1280 0 1390 0 dual 0 14 bands Part III RF _130 RR 157 244 325 610 1060 1170 1280 1390 614 RF_175 LO1_130 LL 157 244 325 610 1060 1170 1280 1390 244 RR 223 310 255 540 990 1100 1210 1320 680 While Observing LO1 175 LO4 130 LO4_175 LL 223 310 255 540 990 1100 1210 1320 310 RR LL 66 66 70 70 70 70 70 70 66 IF BW 32 6 BB ALC BW QOO OO LT Z Z Z Z ZZZ 5 During the Observations The information which has previously been obtained during the preparation Section 4 stage is now brought to and applied during observations Aside from the source file and the command file which the user must prepare in advance the other informa tion can be provided to the telescope operators observers during set up It is the user s responsibility to ensure that the observational set up is correct however so it is important to monitor and check each step of the set up and observing operations There are several other files at this point of which the user should be aware and which the telesc
32. axial cavity Dual concentric coaxial cavity Half wave dipole over ground plane amp a beam forming ring Kildal feed Corrugated horn Table 6 Feed description 151 Primary Beam arc min 18646 Receiver Temperature Tg 144 Typical Ta off Galactic plane 308 Total System Temperature K 482 Tn 3k Tus sb Terima Antenna Temp K Jy Antenna 0 33 Synthesised Beam arcsec Whole Array 20 Central Square 420 Largest Detectable Source arcmin 68 Usable Frequency Range MHz Reliable 150 156 With some Luck 150 to 158 Fudge Factor actual to estimated Short Observations 10 Long Observations 5 Best rms sensitivies achieved so far as known to us mJy 1 5 Typical Dynamic Ranges gt 1000 235 114 5 95 99 177 0 33 13 270 44 232 to 244 230 to 250 0 6 gt 1000 Frequency MHz 325 610 81 4 43 3 50 60 40 10 108 92 0 32 0 32 9 5 200 100 32 17 315 to 335 305 to 360 2 2 2 1 0 3 0 02 gt 1500 gt 1500 Table 7 Measured System Parameters of GMRT 16 590 to 630 570 to 650 1420 24 2 1400 f 40 4 76 0 22 2 40 7 1000 to 1450 950 to 1450 0 03 gt 2000 System Settings IF bandwidths 32 16 6 MHz Baseband bandwidths 16 8 4 2 1 0 5 0 25 0 12 0 062 MHz Polarisation swap Swap on 1 Swap off 0 Table 8 Table showing IF baseband bandwidths and polarisation swap 4 Choose a bandwidth Av see Table 2 from the available bandwidths and c
33. determining a bandpass solution 6 1 Interference Monitoring Spectrum analyser in the reciever room shows two kinds of outputs 1 output from the optical fibre displaying 130 and 175 MHz channels and 2 the baseband output displaying the USBs and LSBs The spectrum analyser output from optical fibre is shown in the Figure 11 6 2 Running AIPS at the GMRT Machines astrol astro2 astro3 astro4 are generally available for the observers on priority basis Please get visitors login and passwd from the local system administrator on these machines Aniruddha B Adoni and or Mangesh Umbarje You would use analysis yourname as your working data area on any one of them Your data on mithuna machine rawdata 6jun yourfile lta is visible on all other machines at the GMRT You also have to source astro RC csh or source astro RC if you wish to use local packages e g gvfits tax etc 39 ACQ STAT STRTDMP ACQ STAT STRTDMP ANTENNA C14 TIME Wed Jul 03 09 57 41 2002 ANTENNA C14 TIME Wed Jul 03 09 57 41 2002 Active Point H C02 1 H H Active Point C10 T C14 T T T Wo01 S06 W02 40 00 50 00 60 00 Power dBm Power dBm 70 00 U 80 00 90 00 100 110 120 130 140 150 160 170 180 190 200 210 100 110 120 130 140 150 160 170 180 190 200 210 Freq MHz Freq MHz
34. ds the U130 and U175 selfs but both will be available only when one merges the data streams You can merge the lta and Itb files using Itamerge This merged file will have the complete data and is easier for playing around with taxx The merged file can be converted to FITS using listscan and gvfits These pro grams are also backwards compatable The individual lta b files can also be converted using these programs but I don t seem to be able to get AIPS to understand the polarizations in a file with only RR RL or only LL LR I think that only some partitioning produced by the VLA correlator is understood The combined RR RL LR LL FITS file is interpreted without problem e In online machine User0 window gt cmode 3 1 for USB 2 for LSB 3 for both gt tpa 11 15 gt allant puts all 30 antennas in array gt initndas temp2 data corrsys hdr 12 gt suba 4 subarray number for which project is to be started gt prjtit title The title for the project upto 80 characters gt prjobs Yourname TST or Name of Observer upto 8 characters gt ante 10123 10 or allant gt initprj 15 PRJCODE 3 for USB 12 for LSB 15 for both e From User4 of online gt tpa rf rf lol lol 104 104 Here rf is the frequency of the band edge channel 0 101 is the frequency of the first local oscillator 104 is the frequency of the fourth local oscillator e g tpa 325 325 255 255 70 70 See Sections 4
35. e bandmask is 12 e g LsbPolar LsbCopy AIIL130 For a dual sideband observation the bandmask is 15 e g IndianPolar The actual bandmask for each mode is tabulated below NB All of these modes use both halves of the correlator so will use CMODE 3 in ONLINE Start and stop scans record as usual Median filter can be used as always it is upto the user to decide if s he wants median filter or not The maximum filter length is 128 RECORD NOW TAKES AN ADDITONAL OPTION SELF IF THE LAST OPTIONAL ARGUMENT IS SELF THEN RECORD WILL PUT ONLY THE SELF CORRELATIONS IN THE LTA FILE For example 11 Bandwidth Samp _freq Samp rate CLK SEL Channel width Possible IF BW MHz MHz u sec kHz MHz 16 32 0 03125 0 125 0 32 16 8 16 0 06250 1 62 5 32 16 6 4 8 0 12500 2 31 25 32 16 06 2 4 0 25000 3 15 625 32 16 6 1 2 0 50000 4 7 8125 32 16 6 0 5 1 1 00000 5 3 90625 32 16 6 10 Table 4 Bandwidth CLK_SEL and IF selection gt record TEST test lta 8m self will create a file test lta with only self correlations in it NB In the new modes the data is divided between the two halves of the correlator For example in the UsbPolar mode U130xU130 and U175xU130 come in mithunb i e the Itb file while U175xU175 and U130xU175 come in mithuna i e the ta file Hence a dasmon in mithuna or mithunb will only show you one half of the data b normalization cannot be applied in some modes To normalize U175xU130 one nee
36. e on source 3C468 1 project 01TSTO1 at a frequency of 1060 MHz 30 b Figure 3 Here all the antennas were used for the observations The C04 E04 S01 W03 and W04 were down at both polarisations whereas S04 and W02 may be WO1 as well was down in one polarisation only either 130 or 175 MHz The observations were made on source 3C147 source c Figure 4 Something that an astronomer would love to see This is an example where all antennas are healthy User should compare the cross correlation shown in this figure Figure 4 with the one that is theoretically expected using above relation dasmon also allows see Figure 5 below the user to continuously monitor the amplitude and phase of the source being observed For the sophisticated user this is fairly useful in determining the stability of amplitude and or phase i e especially during scintillation and fringe winding Figure 5 An example of the mon tcl display ondisp Task ondisp see Figure 6 allows a user to keep track of antennas which are in healthy state Each antenna shows a flag associated with it A few of the key flags means as follows t timeout Z slewing b brake B azimuth brake w wind m mem monitor amp control module time out tax Task to extract data from a GMRT LTA file with optional averaging in time and selection on time baselines frequency channels and on scans via the object name and or scan number
37. generally on The final bandwidth can be chosen from 64 kHz to 16 MHz in factors of 2 for each of the two sidebands The baseband signal is then fed into a sampler followed by the correlator 3 GMRT system 3 1 The Control System Ours is an interactive control mode so that control of the telescope and its observing functions can be changed very quickly Our conceptual model for this therefore is a control panel where someone dials in the desired values and pushes a button to make the whole thing go The online displays the status of the telescope position rates reference position time the setup of various front and back ends information on the procedure that is being run and so on on different screens For each of the items on the control panel there would be a display of the current value e g the exact position of the telescope at that instant The observer s inputs simply generates a setup that is sent to the online through the operator Presently the control panel mode of program control is in its infancy Soon like other observatories we would be able to do away with a machine readable input file and this would update the variables This would provide a way to design an experiment entirely as a real time operation instead of specifying altering various states of the control panel i e observer submits a file generated for his her observations The following settings are usually done by the telescope ope
38. gosacout sndsacsrc 1 12h time 5m strtndasc time 10m hold stabct time 10m stpndasc stpsactrk gtsrc 1637 626 goout gosacout sndsacsrc 1 5h time 6m 1 gtsrc 1637 626 goout gosacout sndsacsrc 1 12h time 2m amp strtndasc time 10m stpndascan stpsactrk gtsrc N6503 goout gosacout sndsacsrc 1 5h time 2m strtndasc time 10m hold stabct time 10m it s generally best to use goout As above but required for the subarray controller The choices are gosacout and gosacin Slew to the source and start tracking 1 for up to 5 hours 5h Do not do anything for 5 minutes in order to allow the array to reach its target Start the correlator and collect data Continue to collect data for 10 minutes Release the brakes hold in case minor wind gusts have resulted in the brakes being applied automatically at some point during the observations For strong winds an alarm will sound in the control room And set the time at the antenna based computer stabct Keep collecting data for another 10 minutes Stop the correlator i e stop collecting data Stop tracking Get and precess coordinates for the second source here the phase calibrator starts the loop 46 hold stabct time 10m hold stabct stpndascan go to 1 returns to the beginning of the loop end A few examples of command files are shown below each column is an independent command file 47 cmode 1 addlist
39. have 128 channels spread over the baseband bandwidth that you choose Please note that there are three choices for the IF bandwidth 6 16 and 32 MHz Depending on your project the line width will vary from a few km s Galactic lines to a few hundred km s extragalactic lines Select a channel width such that you have at least 2 3 channels across your expected line width Thus 128 xselected_channel_width gives you a minimum bandwidth required The other point to consider now is the desired velocity coverage This is also very project dependent If you are trying to observe multiple transitions within your band e g while observing recombination lines it is desirous to obtain both hydrogen and carbon lines which are separated by 150 km s within the band Thus this might mean compromising your channel width This is a subjective 19 decision The third and last part is the available bandwidths at GMRT You have to make your own decision as to which is the best combination for your project In the new correlator modes you could have 256 channels see section 3 1 2 and or GMRT home page Observing Help Features in the Experimental Stage Determining the LO settings Once you have decided on your observing frequency and the baseband bandwidths you need to figure out the local oscillator settings for GMRT For Galactic and near Universe spectral line observations fine adjustments to the local oscillator frequencies are required
40. his is a SETUPNEW TXT file FRONT END PARAMETERS Give 1420 only for full 1420 band selection select freq of observation 50 150 235 325 610 1060 1170 1280 1390 1420MHz 610 235 select solar attenuator 0 14 30 44 dB 1 for FE Termination 0 14 select polarisation unswapped 0 or swapped 1 0 select cal noise level E HI 0 HI 1 MED 2 LO 3 1 for RF OFF 0 LO PARAMETERS select LO freq 100 1600 MHz 680 310 IF PARAMETERS Default is 14 14 select pre attenuator amp post gain for CH1 0 2 4 30 dB 12 22 12 3 select pre_attenuator amp post_gain for CH2 0 2 4 30 dB 18 18 5 select IF band width for CH1 amp CH2 resp 6 16 32 MHz 32 32 select ALC OFF 0 or ON 1 for CH1 and CH2 1 1 New parameters being added enter NG in time domain 0 25 50 or 100 percent duty cycle enter Walsh Enable 1 or Disable 0 Select the Walsh Group 1 if 00 CL C2 2 if CO C1 C2 3 if C4 C5 C6 4 if C4 C5 C6 5 if C9 C10 C11 6 if C9 C10 C11 7 if C13 C14 SP1 8 if C13 C14 SP1 13 if W1 W2 W3 10 if W1 W2 W3 11 if W5 W6 E2 12 if W5 W6 E2 O E D lt H KF H Select Base BANDWIDTH in 16000 Select BB Gain 0 Low Group 0 or Highr Group 1 C3 C3 C8 C8 C12 C12 SP2 SP2 W4 W4 E3 E3 KHz 130 MHz 175 MHz 130 MHz 175 MHz 130 MHz
41. his will eliminate the central square of the GMRT Decide which calibrator will be used to calibrate the bandpass This is usually the flux density calibrator but could be the phase calibrator for strong low frequency sources 7 Create a source file the source file contains the names coordinates and coor dinate epochs of all sources to be observed It is usually named via the initials of the observer e g yourname list lower case Only one such file is usu ally necessary a master list since the file can contain more sources than are 17 10 11 actually observed The format must be exact including spaces and is case sen sitive Thus it is best when first making the file to copy and edit one which is already in existence The telescope operator can supply a template file or see astrol lenyadri shivneri lenyadri odisk gtac source x list There is already a callist file in regular use which includes many calibrator sources including the primary VLA flux density calibrators However it does not con tain all sources in the VLA calibrator manual Therefore it is likely that the phase calibrators will also need to be included in the user s master list of sources Once the source file is created in the user s home directory it should be copied by the telescope operator into a directory which can be read during the ob serving session A sample ONLINE command for loading the file is addlist astrol lenyadri s
42. hivneri lenyadri odisk gtac source yourname list Create a command file see Appendix Z2 in the end of this document and or astro1 lenyadri shivneri lenyadri odisk gtac cmd x cmd for templates This file contains commands for the telescope to slew to a source track collect data for a specified time etc Any of the commands in this file can also be input manually at the console during observations but the file when accessed will prevent the necessity of a continuous input of manual commands It is possible to override this file from the console however when started again it will start from the be ginning of the file so some editing might be required if this occurs Strategically it is best to start the observing run with commands issued manually so as to mon itor a calibrator and correct problems from the console level if they occur Once satisfied the command file can then be invoked A typical example of a command file can be found in Appendix Z2 Command files are usually put in the direc tory e g astrol lenyadri shivneri lenyadri odisk gtac cmd yourname cmd lower case Choose a integration time The integration time specifies the time over which data from the source is collected thus specifying the time interval for an individ ual visibility The integration time is specified through the parameter LTA long term accumulator which is an integral number of STA short term accumulator units the lat
43. hoose a sampling frequency which is twice the bandwidth for Nyquist sam pling The sampling frequency is specified via the parameter clk_sel where 2 x BB samp _freq 32 2 see Table 4 5 Determine the required time on source 7 This is computed via V2 k Toys BELL Na Ne A ny nip Av T where AS is the required rms noise Jy Tsys is the system temperature K and na A 2k G is the antenna gain K Jy where a and 7 being aperture and correlator efficiencies respectively A is the geometrical area of the antenna n is the number of baselines nyp is the number of IF channels and Av Hz is the bandwidth of each sideband or channel width for spectral line observations Here nip npg Nsg where npa is the number of polarisations 2 for the GMRT and nan is the number of sidebands Note that the improvement in S N by operating in double sideband mode applies only to continuum observations The required parameters are provided here 6 Choose a primary flux density calibrator and phase calibrator from the VLA calibrator manual The VLA calibrator manual is also available at the GMRT site The best sources for GMRT use will be those which are usable at all VLA arrays A B C and D However sources which are not acceptable as A array calibrators and possibly B may still be acceptable provided the appropriate uv limits are adhered to It is best not to use a calibrator which is not usable at D array since t
44. is 12 kHz x 128 1 5 MHz Now you have two choices either observe with 1 MHz or 2 MHz Suppose you want a velocity coverage of 200 km s which translates to about 0 95 MHz Thus if you observe with a 1 MHz bandwidth at 1400 MHz you should be able to get your desired velocity coverage and also the desired channel width Having decided on your base bandwidth lets try to determine the LO1 and LO4 required by your observations You can use an IF bandwidth of 6 MHz the lowest available You have determined your central frequency 1420 505 MHz and your baseband band width 1 MHz Using these you have to find out the local oscillator settings Let s use the default LO1 lt RF Then you want 1420 005 MHz in spectral channel 1 and 1421 005 in channel 128 Using tune will give you values of LO1 and LO4 Let s try to do the calculation here For LO1 lt RF RF LO1 LO4 The default set ting for LO4 is 70 MHz so let s assume that LO4 70 MHz This gives a LO1 1420 005 70 1350 005 However since LO1 is allowed only in steps of 5 MHz we can only set 1350 MHz and the 0 005 has to be taken care of in LO4 Thus LO4 1350 MHz Now recalling that RF LO1 L04 LO4 1420 005 1350 0 70 005MHz This will ensure that your HI line falls in the center of the USB Thus you have obtained your tpa as under tpa 1420 005 1420 005 1350 1350 70 005 70 005 For 1 MHz baseband CLK_SEL 4 The frequently used baseband bandwidths at GMRT
45. n 0 select polarization unswapped 0 or swapped 1 select cal noise level E HI 0 HI 1 MED 2 LO 3 1 for RF OFF LO PARAMETERS select LO freq 100 1600 MHz 308 308 IF PARAMETERS Default is 14 14 select pre attenuator and post gain for CH1 0 2 4 30 dB 16 2 5 select pre attenuator and post gain for CH2 0 2 4 30 dB 16 10 2 select IF band width for CH1 and CH2 respectively 6 16 32 MHz 16 16 select ALC OFF 0 or ON 1 for CH1 and CH2 0 0 New parameters being added enter NG in time domain 0 25 50 or 100 percent duty cycle enter Walsh Enable 1 or Disable 0 Select the Walsh Group Low Group 0 or Higher Group 1 0 BASEBAND PARAMETERS set para 16 onwards 7 Select the antenna group 0 if all ant bb mentioned below x 1 if CO C1 C2 C3 130 MHz 2 if CO Ch C2 C3 175 MHz 3 if C4 C5 C6 C8 130 MHz 4 if C4 Cb C6 C8 175 MHz 5 if C9 C10 C11 C12 130 MHz 6 if C9 C10 C11 C12 175 MHz 7 if C13 C14 SP1 SP2 130 MHz 8 if C13 C14 SP1 SP2 175 MHz 13 if Wi W2 W3 W4 130 MHz x 10 if Wi W2 W3 W4 175 MHz 11 if W5 W6 E2 E3 130 MHz 12 if W5 W6 E2 E3 175 MHz 0 Select Base BANDWIDTH in KHz 16000 8000 4000 2000 1000 500 250 125 62 16000 Select BB Gain 0 3 6 9 12 15 18 21 24 0 Select BB LO Hz Synth
46. nstructions for running the new modes looking at the data in real time or offline and converting to FITS follows e INSTRUCTIONS FOR RUNNING THE NEW CORRELATOR MODES 1 log in to corracqa corracqb corrctl as observer chose the d dvl when prompted for which software system to use This sets the paths and environment variables appropriate for the new development software NB if there are any shared memories floating around from the older das versions you will need to delete them 2 login in to mithuna and mithunb as observer and chose d when promoted for which software system to use Again this sets the paths and environment variables appropriate for the new development software NB if there are any shared memories floating around from the older das versions you will need to delete them 3 login into shivneri lenyadri as observer and cd to home observer dassrv dvl If you want to initialize the correlator run 2 corr init on shivneri lenyadri This will run corr config and newdly config on the corrct PC 4 Choose the observing setup by running gt corrsel on shivneri lenyadri This will setup the file temp2 data corrsel hdr which contains information on how you want the correlator configured corrsel allows a menu based selection of the observing mode integration time clksel etc At the moment the following modes are predefined in corr sel The names are hopefully self explanatory In addition
47. observation log will be e mailed to the respective user after his her observations 41 6 6 Computer Facilities at the GMRT There are many computers placed in terminal room for astronomical data analysis specificaly reserved for GTAC observer also see GMRT Home page Facilities Computers Kindly get the relevant account name and password from System Administrator at GMRT Khodad Or check in the Control Room GMRT for the same In the terminal room a network printer is available called npgcc From a linux machine command to print is lpr Pnpgcc files or lpr files Default data area to get observation files is rawdata for USB data amp rawdatal for LSB data In this area data will be present in the subdirectory called by day and month e g 17may Offline analysis software developed are available For any path confusion always source etc bashrc for bash and etc csh cshre or etc cshre whichever exists for csh or source astro RC for bash shell or source astro RC csh for csh tcsh shell Run the sofrware and say explain This will give help for the softwares usage At present following software utilities exist also see GMRT home page Observing Help Offline data analysis software xtract Extract data from lta file in variuos formats tax Graphical interface to plot the data extracted by xtract listscan List the scan in the ltafile for converting to FITS format gvfits Con
48. ope operator will edit according to user specifications One file is called setupnew txt which sets up the hardware Specified in this file are the observing frequency front end parameters the 1st LO the IF bandwidth and the final baseband bandwidth see also Section 2 The other file of interest to the user is the corrsys hdr file This file contains the LTA Section 4 value and channel selection The user should also check that the ALC Section 2 switches are on As the telescope operator sets up the session the user should particularly check the command e g tpa 1418 1418 1350 1350 68 68 This specifies the sky frequency for both polarisations 1st and 2nd numbers the 1st LO frequency for both polarisations 3rd and 4th numbers and the 4th LO frequencies for both polarisations 5th and 6th numbers As the visibilities are recorded the user should check on the amplitude of the signals from the calibrators For self correlations the amplitudes should be the correlation coefficients i e Tant Tant Toys where Tan SXG S the source flux density Jy G the gain K Jy and Tsys the system temperature K Refer to Tables above in Section 4 for system values These correlation coefficients are shown on the MATMON window see Section 5 2 1 for examples of real time display of cross correlation outputs on a MATMON window A Finally information on troubleshooting is provided in the end Appendix Z3 5 1 Inputs
49. ottom one In S04 the FLAGing 1taflag programme has removed the spikes and the bandshape is fitted with a polynomial 34 155 150 100 100 150 06 0 05 0 04 0 03 0 02 0 01 Figure 9 Amplitude and phases of Primary first scan and secondary later scans calibra tors 3C286 1351 018 respectively on baselines C00 amp C01 upper and E02 E03 amp W06 L o J E X P n a COL USB430 009 22 7 L on a gh 3 J L E E t v J o EP Qe 4 L C01 USB 130 C09 4 L 3k me ml T T d 4 L a x s x E Ps CO0 USH 30 C09 m L x Sox AR x s X L K x X amp 4 L C NE uo 4 L mW UT E 4 L C00 USB 130 C09 i 7 de D iud a i Qe owe 1 22 22 5 23 23 5 24 245 E E06 USB 30 C09 L 3 E NS od o dif J E amm 2a 0 r J L P ae J H E06 USB 130 C09 B m PE n Mb nant x um am 7 E 7 naz E03 USB 130 C09 1 L ae cad cd gag E pr PTS f E03 USB 130 C09 3 E x pp x assi ET ou gt lt iie PE nad x AM E LC x eg rd E XR XE 3 E L E02 USB 130 C09 J E rm T T eo T E L pg ns E KA E02 USB 130 C09 7 aie eta came S 8 B 8 8 R g R lower C09 being the reference antenna amplitude is in arbitrary units 35 150 L S S o 4 SL sieu 139009 f J mn o J L maer f z pi Z n 7 3 E 009 J 2 B E po mean tumba S06 USB 130 C09 7 0 03 H m 0 02 k IR mn m i xm SE b T om 2E m gu ud
50. peed of 40 kmph Tracking and pointing accuracy Specifications 45m 18 54 m 1590 m 0 3 K Jy Quadrupod Altitude azimuth Software Limit 17 90 degrees Hardware Limit 15 110 degrees Software Limit 265 to 265 degrees Hardware Limit 270 to 270 degrees Azimuth 30 degree minute Elevation 20 degree minute Operation upto 40 km h Slew upto 80 km h Survival 133 km h 20x20 mm outer 1 3 area 15x15 mm middle 1 3 area 10x10 mm inner 1 3 area 20 mm outer 1 3 area 12 mm middle 1 3 area 08 mm inner 1 3 area 1 rms at wind speeds of lt 20 km h Table 5 The GMRT specifications 2 Check the latest antenna status with telescope operators to see which antennas are available and the central square and complete Y configurations to see that the uv coverage is adequate For spectral observations fudge factor is close to 1 3 Determine the source rise set times At the NCRA Pune this can be accom plished using the utility tact see man tact for an explanation At the GMRT Khodad the ONLINE command gts will accomplish this provided a source file has been created and loaded see Appendix Z2 Also you can use from GMRT home page Observing Help For GMRT Observations for finding source rise set times 15 Frequency MHz 50 153 233 610 327 1420 Type of feed Half wave dipole with linear reflector Two Orthogonal pairs or dipole over a plane reflector Dual concentric co
51. r determine how much slewing time is required between calibrators and source If this is the case then lines 5 to 23 of this file would be omitted and the resulting file implemented after the first scan of the phase calibrator is found to be okay Note that there is no allowance in this file for a flux density calibration scan in the mid point of the observations or at the end In order to insert such observations the user must manually stop this file and issue commands from the console If the file is restarted it will start from the beginning There is also no end to the file since the loop once entered has no graceful exit The session will stop when commands are issued from the console to stop it If the array reaches its altitude limit i e the source sets first then it will continue to collect data as instructed in this file while pointing at blank sky at the array altitude limit currently 17 degrees cmode 1 Specifies that times are relative rather than absolute suba 4 Specifies the subarray being used addlist online operator source yourname list Ensures that the system can read the source list This must be included in this file even if already done manually at the console lnkndas gtsrc 3c286 Gets and precesses the coordinates for the specified source goout Specifies the track outer or inner on which slewing should occur The choices are goout or goin For sources in the northern part of the sky 45
52. rators 3 1 1 Setting RF LO IF and BB Every piece of equipment including the telescope has one or more default setups prob ably in the form of macros that may be invoked with a simple command Two or more hierarchies of defaults are also defined to provide complete system defaults e g observing type defaults line continuum pulsar etc subsystem defaults or special purpose defaults For setting the RF LO and IF front end parameters the user needs to edit a file called setupnew txt The path being home operator set user userz setupnew txt where z 1 2 3 4 5 or m for this file and can also be obtained from the telescope operators in the control room and run a proper program which will create control word according the setting de manded in file Then send the control word to the antennas you need Also a cdsetz where z 1 2 3 4 5 or m is the general purpose aliasing done to ease editing of the proper parameter file setupnew txt An example of a parameter file is as follows This is an example of parameter file To change the parameters you have to change the corresponding entries The lines starting with are comments lines for guiding the user More information on selected parameter is available here this is a SETUPNEW TXT file FRONT END PARAMETERS select freq of observation 50 150 235 325 610 1060 1170 1280 1390 MHz 235 select solar attenuator 0 14 30 44 dB 1 for FE Terminatio
53. roi listscan rawdata T7jun O1TSTO1 0BJ 1ta astroi vi O1TSTO1 0BJ log astroi gvfits O1TSTO1 0BJ log This makes an output file TEST FITS gvfits will not work on any files that have been processed by offline programmes e g 1tacleanup tmac This is because these programmes delete elements of the header that gvfits needs Start AIPS using following commands astrol gt newgrp aips astrol gt source usr aips LOGIN SH for bash shell astroi source usr aips LOGIN CSH for csh tcsh shell astrol gt aips Begin START AIPS and load this file 01TSTO1 FITS into AIPS using FITLD task and follow your favourite way of reducing the data The logflags files can be used as an input in gvfits to flag bad data reported by ONLINE while your observations were made 6 4 Backing your DATA The data backup facility at GMRT Section 6 4 includes several 4mm dat tape drives for 24 GB dat tapes DDS3 These machines with corresponding tape drive DAT tape drive or Exabyte tape drive are as follows dev nst1 astrol machine 4 mm DAT tape drive dev nstO astro2 machine 4 mm DAT tape drive dev rmt 3hn chitra machine 8mm Exabyte tape drive Also you can also copy your LTA files rawdata 7jun 01TSTO1_lta or 01TSTO1 FITS using DAT tape trive on mithuna machine dev nstO mithuna machine 4 mm DAT tape drive dev nstl1 mithuna machine 4 mm DAT tape drive 6 5 Your observation log The
54. ted on a particular date are collected into the directory e g rawdata 1 date the disk is mounted on mithuna b is visible from all other PCs These data are in LTA format and will have an extension of x lta b on the filename A variety of soft wares are available for examining these data in this format See GMRT home page Observing Help offline data analysis software The most useful for on site diagnostics is xtract tax To run most of this software the user must first type source astro RC csh or source astro RC The same software is also available at the NCRA and is sourced in the same way The programme ltacomb is useful to concatenate multiple files and the programme gvfits is required to convert the data into FITS format for later reading into the Astronomical Image Processing System AIPS of the NRAO Spectral line observers who wish to make Doppler corrections can run dopset again source astro RC Within AIPS the user will first have to run INDXR and it may also be necessary to run UVSRT Even for the continuum observations a bandpass calibration is required so the user should proceed with data reductions as for a spectral line data set and then average the channels later using SPLAT or SPLIT Since there is no CHANNEL 0 data set for initial calibration one possibility for a sufficiently strong calibrator is to first calibrate in time on a single channel and then to apply this calibration when
55. ter being the shortest sampling time allowed by the correlator One STA 132 096 milliseconds so LTA 128 corresponds to 16 908 seconds If a 10 minute scan is specified there would be 35 record 60 x 10 16 908 points in your datafile Choose the BB bandwidth see Table 2 The BB should be at least as large as the final IF width but much larger could introduce unwanted interfering signals Choose a sideband and determine the frequency of the 1st LO For lower sideband LSB operation voi gt Var and vpo1 VLo4 vgg where ro is the local oscillator frequency to 70 MHz is the IF and nr is the sky observing frequency For upper sideband USB operation VRF gt VLo1 and VRF vio4 voi The tuning is set to match the 1st channel not the centre of the band and 18 the user should note the permitted frequency increments see Section 2 Also note that there may be other technical considerations which limit which sideband can be used at any time The user should check with a local expert The user can also use the programme tune available locally 4 1 Spectral line observing with GMRT This section is for users interested in spectral line observations with GMRT Observer must be aware that GMRT always observes in the spectral line mode The FX correla tor always generates 128 channels per sideband for the selected baseband bandwidth This is useful since one can take care of bandwidth smearing and also fixed delay effects
56. to the operator in the GMRT Control Room A file via email or personally with the following inputs From Your Name To The GMRT control room The settings are Source OBJECT 26 ProjCode O1TSTO1 Phase Cal phas_cal Flux Cal 3C48 before the command file 3C147 after the command file Command file odisk gtac cmd yourname yourname cmd Source list odisk gtac source yourname list Settings BAND 1280 MHz L01 1215 MHz L04 74 6 MHz IF 16 MHz BB 1 MHz CLK_SEL 4 tpa 1289 6 1289 6 1215 1215 74 6 74 6 Note Please observe 3C48 for 20m before the target source rises and observe 3C147 for 20m after the target source sets Use LTA2 8m for 16sec integration The CLK_SEL for various baseband frequencies are given in Table 4 it can also be found using E baseband BW and 32 samp_freq Aca 5 2 Data quality and monitoring The purpose of on line data monitoring is to provide a running check on data integrity and proper operation of the system User and operator interaction is limited to selecting the type and options of the display appropriate to the data being collected plus some scroll back through the most recent displays Although the telescope operators are fairly helpful during the observations and knowl edgeable it is the user who is responsible for ensuring that the observatinos run smoothly and correctly The telescope operator is responsible only for seeing that the d
57. vert GMRT lta data to FITS format Itahdr Gives info about lta file scan wise aon d NH ltacomb Concatenate number of lta files to one lta file To use aips on these machine after logging do following 1 newgrp aips 2 source usr aips LOGIN CSH for csh or source usr aips LOGIN SH for bash 3 aips 4 Prefer to use aips id 1010 1020 and 1030 on astrol astro2 and astro3 respectively 5 There is DATA partition kept for aips data purpose 0 Also analysis local disk space is available Important No backup is taken for DATA and analysis area and user has to take his own backup before he leaves GMRT site Data in this area will not be available after that more than a day kindly note DDS 3 tapes can be bought at GMRT 42 6 7 Computer Facilities at the NCRA You can use the a computing facilities at the NCRA for your data analysis please contact V Venkata subramani system administrator or Shekhar Bachal for accessing visitor GTAC ma chines b many of the machines in the common computing facility are equipped with either DAT tape DDS3 drive to load and or back up your data Acknowledgements This document involves inputs from several people particularly those associated with the GMRT We express our thanks to everyone of them Document updated on 4th July 2006 by Manisha Jangam amp D J Saikia 43 Appendix Z1 Feedback Please provide us feedback by filling up the Observer
58. you can configure a vast number of modes by editing the DPC_MUX and MAC MODE fields in the corrsel hdr file The valid MAC MODE values are RRLL RRRL and RR The valid DPC_MUX values are any of the strings IndianPolar UsbPolar LsbPolar UsbCopy LsbCopy new modes A11U130 A11U175 A11L130 A11L175 arar _arar alal _alal brbr _brbr blb1 _blbl historical aral _brbl aral _alar brbl _blbr arbr _albl Code T IndianPolar UsbPolar LsbPolar UsbHighRes LsbHighRes UsbCopy LsbCopy AllU130 AllU175 AllL130 AIIL175 0 1 2 3 4 5 6 7 8 9 1 Table 2 Correlator Modes Again the names should be self explanatory In addition the mode can be a string of the form dpc_abcd where 0j a b c d j 3 A mode of the form dpc_abcd means that the dpc mux sends channel a data to where channel 0 data normally goes channel b data to where channel 1 data normally goes and so on NB In the UsbHighRes and LsbHighRes modes the DPC_MUX is set to UsbPolar and LsbPolar respectively However the MAC_MODE will defer for the HighRes and Polar modes reconfigure the correlator to the selected mode To do this type gt corr reconf on shivneri lenyadri PLEASE NOTE THAT IF YOU ARE CHANGING THE MODE IT IS NECCESSARY TO DO A hltndasc AND RESTART acq30 ETC IT MAY BE SAFEST TO KILL AND RESTART ALL THE acq PRO GRAMMES NOT KILLING acq MAY AFFECT SYNCHRONIZATION OF THE TWO PIPELINES MOST OF THE TIME IT SHOULD BE FINE TO KE
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