====== Heterodyne Observations ====== This is a brief introduction to heterodyne observing at the CSO. It continues from the general [[.:..:..:observing:operating]]. * [[#Quick Start]] * [[#After Observing]] * Preparation * [[heterodyne]] systems description * [[obstime]] calculation * Source and line [[cso:telescope:uip:catalog|catalog]] preparation * Planning for [[wideband]] * [[http://cso.caltech.edu/atm/tuning.html|Receiver tuning diagram]] * Tuning [[.tuning:sidecab|narrow band]] and [[.tuning:barney]] receivers * Types of Observations * [[chop]] * [[onoff]] * [[pointing]] * [[fswitch]] * [[mapping|Mapping]] * [[otfmap]] * [[calibration]] * [[#Sideband Identification]] * [[analysis]] * [[#Troubleshooting]] ===== Quick Start ===== This guide outlines a common observing scenario, simultaneous [[chop]] observations of [[wideband#example_1|three CO isotopologues]] in the (2-1) lines. There are many possible variations. - [[cso:observing:remoteobs#connect_to_the_vnc_desktop|Connect]] to the VNC desktops. Two desktops are used, one for the UIP and the other for the spectrometer displays. (This is more flexible than one large desktop.) \\ ''mycomp> ** csovnc.pl -C -l //user// uip ** '' \\ ''mycomp> ** csovnc.pl -C -l //user// spectro ** '' * In the UIP desktop, there are two xterms on the right side: - The upper one displays the telescope status, updated once per second. - The lower one is for the UIP. - In the UIP xterm, log into your account then start UIP. \\ ''kilauea% **ssh //user//@kilauea**'' \\ ''kilauea% **uip**'' - If necessary, enable control mode. \\ ''UIP> **pundit true**'' - Open the [[cso:telescope:shutter|shutter]]. Avoid the sun. When remote observing, wait until one hour after sunset. \\ ''__UIP__> **shutter /open** '' - Create a data file. \\ ''__UIP__> **data //yyyy-mm-dd//**'' - Open source and line [[cso:telescope:uip:catalog]], if necessary. \\ ''__UIP__> **catalog //sources//**'' \\ ''__UIP__> **catalog //lines// /line**'' - Start the [[cso:telescope:secondary]] wobbler for [[chop]]. Tuning the servo takes about 5 min. For example, 120 arcsec amplitude at 0.534 Hz. \\ ''__UIP__> **secondary 120 0.534**'' * Check the status of the servo tuning. \\ ''__UIP__> **secondary** '' - Select the receiver and verify the teritary mirror position. * For the sidecab receivers, first place the telescope at 25° zenith angle. \\ ''__UIP__> **za 25** '' \\ ''__UIP__> **instrument [RX230 | RX345 | RX460 | RX690]**'' \\ ''__UIP__> **tertiary /sidecab**'' * For the Cassegrain receivers, first remove the mirror covers and manually rotate the tertiary mirror. \\ ''__UIP__> **instrument [RX345X | RX805]**'' \\ ''__UIP__> **tertiary /cassegrain**'' - If necessary, load the appropriate pointing file. \\ ''__UIP__> **point //rx_name//**'' - Tune the receiver. For example, the standard tuning for [[wideband#example_1|three CO isotopologues]]. \\ ''__UIP__> **lo 12co2-1 /side up /if 5.28**'' \\ Older receivers require manual tuning. * [[.tuning:sidecab]] * [[.tuning:barney]] - Configure the spectrometers ([[ffts1|FFTS1]], [[ffts2|FFTS2]], [[aos5|AOS5]]). \\ ''__UIP__> **spec 2 /ffts2 /ffts1w 5.28 /res ** '' * For the older narrow band receivers, turn on the [[aos5#IF processor]] {{ifprocswitch.jpg?linkonly|switch}} in the [[aos5|AOS5]] {{aos5rack.jpg?linkonly|rack}}. - [[calibration|Calibrate]] and measure the system temperature. \\ ''__UIP__> **cal**'' - Measure the [[pointing]] with [[chop]]. \\ ''__UIP__> ** spec /base 2500 3500 4700 5700 **'' \\ ''__UIP__> **five 20 /ffts1 /range 4000 4200 ** '' * Use the [[cso:telescope:orrery]] to select pointing sources. - Take a reference spectrum of the pointing source with [[chop]]. \\ ''__UIP__> **chop 2**'' * Maybe useful as a [[calibration]] reference. - Track the target source. \\ ''__UIP__> **obs //target//**'' - [[calibration|Calibrate]] and measure the system temperature. \\ ''__UIP__> **cal**'' - Set the integration time. \\ ''__UIP__> **spec 10**'' - Observe the target. * With [[chop]]. \\ ''__UIP__> **chop 10**'' * For [[onoff]], first stop the [[cso:telescope:secondary]] wobbler. \\ ''__UIP__> **secondary /stop **'' \\ ''__UIP__> **oo 10**'' ===== After observing ===== - Close the [[cso:telescope:shutter|shutter]]. This takes 10-15 min. When remote observing, please close one hour before sunrise. \\ ''__UIP__> **shutter /close**'' * If the shutter doesn't close, follow these [[cso:telescope:shutter#troubleshooting|instructions]]. Please report problems to the staff. - Stow the telescope \\ ''__UIP__> **stow**'' \\ After sunrise, wait until the shutter is no more than 15% open before using the ''**stow**'' command. Please do //not// let the Sun directly illuminate any part of the telescope structure. Check the [[http://www.cso.caltech.edu/webcams.html|CSO webcams]]. - Stop the secondary wobbler \\ ''__UIP__> **sec /stop**'' - Turn off the [[aos5#if_processor|IF processor]] in the [[aos5|AOS5]] rack. - Turn off the receiver. * For the 230/460 GHz receiver: \\ ''__UIP__> **lo /off**'' * For the older receivers: [[cso:instruments:heterodyne:tuning:sidecab#shutdown]] procedure * For Barney: [[cso:instruments:heterodyne:tuning:barney#shutdown]] procedure - Replace the Cassegrain mirror covers. - Exit from the UIP. \\ ''__UIP__> **exit**'' - Exit from your account but please do not close the UIP xterm in the VNC desktop. - Stow any ladders or other equipment. - Return the pointing log book to the shelf. \\ Heterodyne observers please add your nightly pointing sheet to the end the log book and return the book to the bookshelf. - Please submit an [[cso:observing:obsreport]]. - Logout from kilauea and other computers. - Turn off all the lights and heaters in the building. Lock both entry doors. // Drive safely! // ===== Sideband Identification ===== The CSO has DSB receivers with equal gain in the two sidebands. To determine if specific lines are in the upper or the lower side band, change the LO frequency. Lines in the two sidebands will shift in opposite directions. Lines in the image sideband will shift twice as far as lines in the signal sideband. * To change the LO by 5 MHz, \\ ''__UIP__> **lo /f_off 0.005**'' If the atmospheric transmission in the two sidebands is different, [[calibration]] correction will be necessary. ===== Troubleshooting ===== * If the system temperature is unreasonably high for the [[http://www.cso.caltech.edu/tau|optical depth]] (//τ//) or [[cso:weather:weather|weather]] conditions. * Is the [[aos5#if_processor|IF processor]] in the [[aos5|AOS5]] rack on? * Is there a warm load or something else in the beam? * Are the cassegrain mirrors uncovered? * Is the position of the tertiary mirror correct? * Are the sidecab mirror positions correct? To reposition them, \\ ''__UIP__> **za 25**'' \\ ''__UIP__> **lo //line// /receiver //rx_name// /force** '' * Is the line frequency close to an atmospheric line? \\ Check the [[http://www.submm.caltech.edu/cso/weather/atplot.shtml|atmospheric transmission]]. * Is the [[cso:telescope:shutter|shutter]] closed? * Is the [[http://www.cso.caltech.edu/tau|optical depth]] (//τ//) high and the zenith angle large?\\ Wait for the source to rise. * Is the [[cso:weather:weather|weather]] worse than you thought? * Is the [[.tuning:sidecab#345ghz|345 GHz sidecab receiver]] tuned to the fifth harmonic? * If there's no line even though the system temperature is reasonable and the source should have a bright line. * Is the correct pointing model displayed on the antenna status monitor? * Is the pointing good? * Is the frequency correct? Check the catalog. * Is the receiver tuned properly? * If the spectrometer stops, restart it (specify the backend). \\ ''__UIP__> **spectrometer /restart /ffts2 ...**'' === === These older documents may contain obsolete information. Use with caution. * {{cookbook.pdf|Cookbook}} 2011-06-22 * {{checklist.pdf|Checklist}} 2011-06-22