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The Robert C Byrd Green Bank Telescope

The Robert C Byrd Green Bank Telescope. VLBI usage: About 15% of GBT time goes to VLBI projects. Including 2 Large projects: Megamaser cosmology Planet Search Also HSA, globals, EVN. Frank Ghigo, National Radio Astronomy Observatory US VLBI Meeting, Socorro, Nov 2011.

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The Robert C Byrd Green Bank Telescope

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  1. The Robert C Byrd Green Bank Telescope VLBI usage:About 15% of GBT time goes to VLBI projects.Including 2 Large projects: Megamaser cosmology Planet SearchAlso HSA, globals, EVN Frank Ghigo, National Radio Astronomy Observatory US VLBI Meeting, Socorro, Nov 2011

  2. Subreflector and receiver room

  3. On the receiver turret

  4. Inside the receiver room

  5. GBT active surface system • Surface has 2004 panels • average panel rms: 68  • 2209 precision actuators

  6. GBT Receivers

  7. dbe0 = RDBE(0, 'ddc') dbe0.setALC(1) dbe0.setFormat('Mark5B') dbe0.setPSNMode(0) dbe0.setPacket(0, 0, 40, 5008) subarray.setDBE(dbe0) loif0 = VLBALoIfSetup() loif0.setIf('B', '4cm', 'R', 9100, 'L') loif0.setIf('D', '4cm', 'L', 9100, 'L') loif0.setPhaseCal(1) loif0.setDBEParams(0, -1, -1, 10, 0) loif0.setDBEParams(1, -1, -1, 10, 0) loif0.setDBERemember(0, 1) loif0.setDBERemember(1, 1) channelSet0 = [ \ bbc(0, 715.51, 16, 'L', 2, 0), \ bbc(1, 715.51, 16, 'L', 2, 0), \ bbc(0, 699.51, 16, 'L', 2, 0), \ bbc(1, 699.51, 16, 'L', 2, 0), \ bbc(0, 683.51, 16, 'L', 2, 0), \ bbc(1, 683.51, 16, 'L', 2, 0), \ bbc(0, 667.51, 16, 'L', 2, 0), \ bbc(1, 667.51, 16, 'L', 2, 0) \ ] source0 = Source(2.34113879064523, 0.344670647860465) source0.setName('J0856+1944') source1 = Source(2.34851709074009, 0.344927178341659) source1.setName('GJ1116A') source2 = Source(1.99207777262673, 0.550207658130712) source2.setName('J0736+3131') source3 = Source(1.9836550615079, 0.556220267002602) source3.setName('GJ278C') BB240GD.GB.py • import os • isAstrid = 0 • if 1: • try: • if os.getenv('ASTRIDVLBA') == '1': • isAstrid = 1 • except: • pass • if not isAstrid: • from edu.nrao.evla.observe import Mark5C • from edu.nrao.evla.observe import MatrixSwitch • from edu.nrao.evla.observe import RDBE • from edu.nrao.evla.observe import VLBALoIfSetup • from edu.nrao.evla.observe import Parameters • from edu.nrao.evla.observe import bbc • second = 1.0/86400.0 • deltat2 = 1 • obsCode = 'BB240GD' • stnCode = 'GB' • mjdStart = 55822 + 37800*second • recorder0 = Mark5C('-1') • recorder0.setMode('Mark5B') • recorder0.setPSNMode(0) • recorder0.setPacket(0, 0, 40, 5008) • subarray.setRecorder(recorder0) • :

  8. More BB240GD.GB.py • # Scan 1 = No0002 • # pointing scan for the GBT • subarray.setSource(source4) • recorder0.setPacket(0, 0, 40, 5008) • if isAstrid: • source4.setPeak(True) • subarray.setRecord(mjdStart + 661*second, mjdStart+1141*second, 'No0002', obsCode, stnCo • de ) • if array.time() < mjdStart + 1141*second: • subarray.execute(mjdStart + 475*second) • else: • print "Skipping scan which ended at time " + str(mjdStart+1141*second) + " since array.time is " + str(array.time()) • source4.setPeak(False) • # Scan 2 = No0003 • subarray.setSource(source8) • recorder0.setPacket(0, 0, 40, 5008) • subarray.setRecord(mjdStart + 1300*second, mjdStart+1340*second, 'No0003', obsCode, stnCode • ) • if array.time() < mjdStart + 1340*second: • subarray.execute(mjdStart + 1136*second) • else: • print "Skipping scan which ended at time " + str(mjdStart+1340*second) + " since array.time is " + str(array.time())

  9. 500-1000 MHz filter

  10. 500-1000MHz filter, zoom

  11. 90 GHz observing in Green Bank?? • ~500 hours per year with t< 0.1 and winds < 3 m/s • Surface rms ~ 240m , aperture efficiency ~30% at 90 GHz • Tracking, 9” beam • Half-power tracking tests: about 1” rms over 15 min • Offset pointing : about 2-3” rms • Pointing, servo Improvements • Pointing model, including thermal effects • Servo upgrades – digital servo system for Az and El motions • Eliminate servo resonances • Minimize structural resonances, reduce settling time

  12. Tracking at half-power

  13. 4mm receiver 68-92 GHz

  14. 4mm receiver – inside the dewar

  15. Calibration turntable

  16. ¼ wave plate

  17. 4mm receiver in the turret

  18. Tsys calibration • Tsys is be calculated from power measurements synchronized with the hot/cold load settings. • Measurements will be done at intervals of a few to 60 minutes. • For VLBI, ideally the RDBE will measure power in each channel, from which Tsys can be calculated if the state of the calibration wheel is known. • In general, the DCR (digital continuum receiver), running in parallel with other back ends will detect total power in the IF and its data can be used to calculate Tsys; the values will be made available in a table. • But DCR inputs follow IF bandpass filters of 80, 240, or 1280 MHz.

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