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LRO MiniRF experiments at the NRAO-GBT: August 2009

Project code: AGBT09A_070

Session Date Comment
AGBT09A_070_00 Aug 12-13 Prelim checks of scripts during maintenance time
AGBT09A_070_01 Aug 15 Test the ephemeris, check pointing, look for downlink at 2271.2MHz
AGBT09A_070_02 Aug 22 11:00 - 15:00 UT Observe miniRF boresight, check and adjust levels
AGBT09A_070_03 Aug 23 15:00 - 21:00 UT Observe miniRF beam sweeps
AGBT09A_070_10 Aug 24 9-12am EDT Linearity checks, recording SP and DCR
AGBT09A_070_11 Aug 24 9-12am EDT Linearity checks, recording with GASP.
Session Date Comment
AGBT09A_070_04 Aug 30 17:15 - 22:15 UT Polarization calibration: observe 3C286

Session 1 Aug 15, 2009 - check ephemeris 

 Log of LRO pointing Sat morning AUg 15 11:15 UT, project code is AGBT09A_070_01 

 

11:22 UT Sband in place, slewing to the Moon
  scan 1 spectrum -- no sign of the 2271.2 signal
  scan 2 ?
  scans 3-6 cross scan -- the moon shows up, but no LRO
  scans 7-10 peak on calibrator 0534+1927              lpc=+0.043, +0.195'

  scan 11 - track, collect SP data, no 12db in receiver -- no signal seen
  scan 12 - another spectrum, but sdfits did not see it??
  scans 13-16 cross scan on LRO ---               LPC = +0.330, -0.788  mostly the Moon (but there is a peak on the side in el)
              pointing fit used the peak.
  scan 17 - spectrum on LRO with latest LPC -- Downlink signal seen 2271.23 MHz !!

  scans 18-21 peak  on LRO                        lpc = +1.035, -0.746'   UT start   11:58:15
  scan 22 another 60 sec spectrum scan.
  23-26 peaks  :                                  LPC= +1.287', +0.084               12:07:23       
  27 - track (60 sec)
  28 - track (60 sec)  ["Balance()" seems to always balance IF rack to 1v, even if target set to 3]
  29-32 peak :                                  LPC = +1.205, +0.758'                12:17:46     
  33-36 peak :                                         1.178, +0.933                 12:23:18
  37-40 peak                                          +1.055, +0.952                 12:29:03         
  41-44 peak with 20 sec scans instead of 40  : LPC = +0.891, +0.893'                12:34:41       
  45-48 peak                                          +0.626, +0.845                 12:39:44
  scans 49-52 peak                                    +0.604,  ***  (LRO has disappeared as of the el scans) 12:44:48


Result: Success!

  • Downlink spectrum, 2271.2 MHz, 60 sec integration:
    LROdownlink.jpg
  • Downlink signal, DB scale:
    LROdownlink db.jpg

Examples of pointing on the LRO signal

These plots show two examples of a pointing sequence (4 scans) on the LRO downlink signal -- the Moon is clearly seen, and the LRO signal peak is much higher; thus the software can solve for a pointing offset. Red is the measured data, green is the fitted gaussian. Note that these pointing data are recorded with the DCR (digital continuum receiver). The measured signal is the total in an 80 MHz band centered on 2271 MHz. Hence the average of the LRO downlink over the 80 MHz band must far exceed the average power from the Moon over that band in order to be able to use it for updating the pointing corrections.
Pointing on LRO, scans 13-15 Pointing on LRO, scans 41-44
peaks lro Aug15 scans13-16.jpg peaks lro Aug15 scans41-44.jpg

Session 2: August 22: 13:00 to 15:00 UT. ( 9 - 11 am EDT)

Observe miniRF at boresight and check power levels.
    Planning timeline
    Time (UT)Moon Az/El What
    13:00 92/ -04 GBT session starts
    13:10-13:45 check pointing, configurations, test spectra with test tone
    14:00 101/ 07.2 verify to LRO we are ready for 2380 MHz MiniRF tx
    14:05 102/ 08.1 about the earliest we can peak on the telemetry
    14:10 103/ 09.0
    14:15 104/ 09.9 miniRF boresight tx begins
    14:29 106/ 12.6 miniRF boresight tx ends
    15:00 111/ 17.9 GBT session ends

Aug 22 observing notes: 

 Start 9am (13UT) 
 -- modify ephemeris for Aug 22 to start at 14h (Moon doesn't rise before then)
    ephem file:  LRO_GBT_2009Aug22A_topo.cat
 Scans 1-4 : peak on pointing cal 1058+0133 (near where Moon will rise)
              peak looks good: LPC = 0.072', -0.063'  Tant=4.9K
 Scans 5-8 : peak up on Venus - looks good; Tant~0.56K
 Scan 9 - one stripe across Venus, collecting data with SP and Gasp
 scan 10   ditto
           Paul reports GASP levels ok
 scan 11-14 peak on 1058 again
 scan 15-16 try to track LRO - elev is low (7.2deg) but tracks ok, and 2271.2 signal is seen clearly
 scans 17-24 try peaks on LRO 2271 - unsucessful - Moon dominates
  • See plot of scans 21-24 -- red is data, green attempt to fit a gaussian. 
                We see the Moon, but no sign of the 2271 downlink signal.
             Curious! we could peak up very well on that signal in the Aug 15 run.
 scans 25-26 track LRO 2271.2 signal
 scans 27,28  track miniRF 2380 -use atten settings decided from Chandrayaan. start at 14:16:50 UT - miniRF is on.
 scans 29-30  miniRF,  use auto level to find optimum settings
 scans 31-32  miniRF,  attens as before but +10db in IF rack (for SP; no change for GASP)
 scans 33-34  miniRF in circular pol, use auto leveling, miniRF turns off during scan 34.
 scans 35-38  cross scan on Moon, circ pol, same attens as 33-34
 scans 39-40  On/Off on Moon, circ pol, no atten change
 scans 41-42  On/Off on Moon, circ pol, auto levelling
  • AGBT09A_070_02.summary: Scan Summary for session 2
  • AGBT09A_070_02_log.txt: Astrid log for session 2 - Aug 22

Attenuator settings for miniRF scans: +12db in receiver for scans 27-34. Paul may have altered the CnvRack setting for GASP from what is listed here.
This table lists the attenuator values that were used, and the peak of each spectrum in counts converted to DB.

miniRF scans, 2380 MHz
Attenuator settings total atten peaks db
Scan# dur pol IFRack CnvRack SpectProc XX, YY XX, YY
27 30 lin 14,8,10,7 12,14,25,30 23,28 49, 50 75.2, 74.3
28 30 lin " " " " 76.6, 75.1
29 30 lin 0,2,1,0 12,14,25,30 40,30 52, 46 75.0, 75.0
30 30 lin " " " " 74.7, 74.9
31 30 lin 10,10, 1, 0 " 40, 44 62, 68 69.2, 72.8
32 30 lin " " " " 69.0, 72.7
LL, RR LL, RR
33 30 circ 0,0,1,0 12,14,25,30 40,35 52, 49 75.3, 76.0
34 30 circ " " " " 74.3, 75.0
As a result of these tests, disscussions ensued about the proper attenuator settings, some of which are captured in this attached e-mail summary email_reAug22.txt: E-mail discussion regarding attenuator settings.

The decision was made to use the settings of Scan#31 with the change that IFRack attenuators would be increased to 16, 16 for S1 and S3 and that S5 and S7 (to GASP) would be left the same.

Example spectra - Aug 22

A couple of examples show spectra of scans 29 and 32; in scan 29 the peak is double, presumably a sign of saturation. Whereas in scan 32, with higher attenuator settings, the peak is clean.
Scan 29 XX spectrum showing bifurcation:   Scan 32 XX spectrum showing clean peak:
Aug22 scan29xx.jpg   Aug22 scan32XX.jpg

-- FrankGhigo - 13 Aug 2009
Topic attachments
I Attachment Action Size Date Who Comment
AGBT09A_070_01.summarysummary AGBT09A_070_01.summary manage 8 K 2009-08-15 - 09:40 FrankGhigo Scan summary for AGBT09A_070_01
AGBT09A_070_01_log.txttxt AGBT09A_070_01_log.txt manage 74 K 2009-08-15 - 09:41 FrankGhigo Astrid Log for AGBT09A_070_01
AGBT09A_070_02.summarysummary AGBT09A_070_02.summary manage 7 K 2009-08-31 - 11:07 FrankGhigo Scan Summary for session 2
AGBT09A_070_02_log.txttxt AGBT09A_070_02_log.txt manage 75 K 2009-08-31 - 11:08 FrankGhigo Astrid log for session 2 - Aug 22
Aug22_scan29xx.jpgjpg Aug22_scan29xx.jpg manage 48 K 2009-08-31 - 11:36 FrankGhigo Scan 29 XX spectrum showing bifurcation
Aug22_scan32XX.jpgjpg Aug22_scan32XX.jpg manage 45 K 2009-08-31 - 11:36 FrankGhigo Scan 32 XX spectrum showing clean peak
LROdownlink.jpgjpg LROdownlink.jpg manage 49 K 2009-08-15 - 14:28 FrankGhigo Downlink spectrum, 2271.2 MHz
LROdownlink_db.jpgjpg LROdownlink_db.jpg manage 55 K 2009-08-15 - 14:29 FrankGhigo Downlink signal, DB scale
Timeline_for_August_LRO_Calibrations_20090814_Update_RCS.docdoc Timeline_for_August_LRO_Calibrations_20090814_Update_RCS.doc manage 276 K 2009-08-15 - 09:54 FrankGhigo Updated Timeline-Aug 14
TimelineforAugustLROCalibrations.docdoc TimelineforAugustLROCalibrations.doc manage 209 K 2009-08-13 - 11:56 FrankGhigo Timeline for August LRO cals, from Ron Schulze
email_reAug22.txttxt email_reAug22.txt manage 6 K 2009-08-31 - 11:23 FrankGhigo E-mail discussion regarding attenuator settings
peak_attempt_Aug22.jpgjpg peak_attempt_Aug22.jpg manage 88 K 2009-08-31 - 11:57 FrankGhigo Scans 21-24: try to peak up on LRO downlink
peaks_lro_Aug15_scans13-16.jpgjpg peaks_lro_Aug15_scans13-16.jpg manage 90 K 2009-09-02 - 13:27 FrankGhigo Pointing on LRO, scans13-15
peaks_lro_Aug15_scans41-44.jpgjpg peaks_lro_Aug15_scans41-44.jpg manage 91 K 2009-09-02 - 13:28 FrankGhigo Pointing on LRO, scans41-44
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