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observing:ragrav

RadioAstron Gravitational Redshift Experiments at Yarragadee

Background

We are participating in a series of observations with the RadioAstron spacecraft where it's downlink signal is recorded by the 12m antenna while the Yarragadee SLR also tracks the spacecraft. The data are only useful if both the SLR and 12m successfully track.

On the 12m, we use the Field System to record the data to the Mark5 and the HMI antenna interface (on the timeyg VNC server) to control the antenna. The RadioAsdtron group provide a file for HMI as well as a VEX file.

Signal path modifications

The receiver cross-over switches have been re-wired to allow additional attenuation in the signal path and/or a reduced supply voltage to the X-band RCP LNA. This is to reduce the signal strength entering the DBBC and hopefully improve phase stability. The S-band cross-over with enables a variable power supply for the LNA when crossed and the X-band cross-over switch will put a (manually configurable) variable attenuator into the X-band RCP signal path after the LNA. The Field System commands to set the 4 possible modes are:

"x-band rcp lna 20V, atten in
rfpic=cross,direct,*
"
"x-band rcp lna 20V, no atten
rfpic=direct,direct,*
"
"x-band rcp lna variable voltage, atten in
rfpic=cross,cross,*
"
"x-band rcp lna variable voltage, no atten
rfpic=direct,cross,*

Processing the antenna pointing files

The tracking file is provided by the RadioAstron group. It must be transferred to the timeyg PC. FTP is probably the easiest method, so place the file somewhere (e.g. fourier) and give it a name with a .txt extension. Open the file with emacs and check that it's in DOS ASCII format. e.g. on Fourier:

emacs -nw <filename.txt>

You should see (DOS) in the lower left corner. If you do, all is well. If not, convert to DOS format in emacs by typing:

C-x RET f undecided-dos

where “C-x” = [Ctrl]-x, RET = the Return/enter key.

On timeyg, open a Command Prompt and type:

cd "C:\Documents and Settings\Astro\RadioAstron"
ftp fourier.phys.utas.edu.au
(log in)
bin
get <filename.txt>
quit

Note the file should be transferred in binary (bin) mode.

Processing The VEX files

  1. Copy the VEX file to pcfsyg:/usr2/sched
  2. On the pcfsyg VNC session:
    1. Open a new terminal window
      cd /usr2/sched
      drudg <filename>.vex
      Yg
      3
      12
      0
      mv <filename>yg.prc /usr2/proc
      emacs -nw <filename>yg.snp
      (comment out the source command(s), then exit emacs)
      cd /usr2/proc
      emacs <filename>yg.prc

We usually modify this to record both polarisations instead of one as there is some leakage into LCP and the signal may be more stable than the very strong RCP tone. Changes need to be made to the following procedures:

  1. In setup01 change the recording mode to
    mk5b_mode=ext,0x0000FFFF,,8.000
  2. The X-band crossover switch has been re-wired to include a step attenuator to reduce the RCP power level. We put this attenuator in by default. We also remove the IF box attenuation. So also add these commands to setup01:
    "X-band RCP LNA on, atten in
    rfpic=cross,direct,*
    "Take out attenuation in X-band, IF rack
    ifpic=*,*,15,15,0,0
  3. Modify the DBBC frequencies to include LCP channels, note the 16273135148x number will be 0000000000x at the start and is written later (I imagine the time it was executed?) :
    define  dbbc014       16273135148x            
    bbc01=798.75,a,4.00
    bbc02=798.50,a,4.00
    bbc03=798.25,a,4.00
    bbc04=798.00,a,4.00
    bbc05=798.75,b,4.00
    bbc06=798.50,b,4.00
    bbc07=798.25,b,4.00
    bbc08=798.00,b,4.00
    enddef
  4. Also add a second IF and LO setting for LCP:
    define  ifd01         16273135148x            
    ifa=1,agc,1,25000
    ifb=1,agc,1,29000
    lo=
    lo=loa,7600.00,usb,rcp,off
    lo=lob,7600.00,usb,rcp,off
    enddef
  5. Lastly, add the checkmk5 procedure:
    define  checkmk5      16273141501x  
    scan_check
    !+1s
    mk5=get_stats?
    mk5=get_stats?
    mk5=get_stats?
    mk5=get_stats?
    mk5=get_stats?
    mk5=get_stats?
    mk5=get_stats?
    mk5=get_stats?
    mk5=status?
    enddef

Setting up

  1. Make sure the antenna is stowed and the drives are off, the Field system is terminated
  2. In HMI:
    1. Go to the SETTINGS tab. Under TIME OFFSET, set UT1-UTC to -0.3 and press “Load New Value”, then [SAVE]
    2. Go to the LOAD TRACK tab
      1. in the [Track Array #2] area, click on [Browse] to find the pointing file you downloaded, then press [LOAD]. It can take several minutes for the file to load and the HMI display will freeze while it's happening. When complete, the time will start updating and you should see “Unused points” less than 2000.
  3. Bring up the VNC display for the spectrum analyser (specyg) set the centre frequency to 800 MHz and the span to 2 MHz.

Running the observations

PC Field System

  1. Start the field system in the VNC session. If you cannot get the field system to run, you'll need to power cycle the pcfsyg through the Internet power switch. Once the pcfsyg comes back online after a boot, ssh into it and start the vnc server by typhing vncserver into the terminal. Now, open the vnc session to the pcfsyg and start the schedule
    schedule=<schedule>,#1
  2. You may get error messages like this
    ERROR st  -28 UT1TimeOffset non-zero, see value above.

    . Silence them with the command

    tnx=st,-28
  3. It's a good idea to monitor total power levels into the DBBC during the observations. Do this with
    iread@!,10s

HMI

  1. Turn on the drives and put the antenna in operate mode
  2. On the [AZEL] tab, select DATA SOURCE to be ARRAY #2, press [TRACK]. The antenna should start tracking the pre-set spacecraft coordinates.

During the observations

Watch out for the spacecraft signal in the spectrum analyser, check both polarisations using ifpic=xr (RCP), ifpic=xl (LCP). Make notes in the log on signal strength etc.

The attenuator values can be changed using the “rfpic=<xband>,<sband>”, replace xband and sband with either “direct” (no attentuation) or “cross” for variable attenuation (Check with yg staff regarding the voltage of the variable attenuation). (Arwin)

After the observations

  1. In the PCFS, stop the power monitoring with a
    iread@
  2. Terminate the field system
  3. In HMI,
    1. Stop tracking in the [AZ/EL] tab with the [STOP] button
    2. stow
    3. set UT1-UTC to 0 in the [SETTINGS] tab
/home/www/auscope/opswiki/data/pages/observing/ragrav.txt · Last modified: 2017/04/22 06:18 by Elizabeth Iles