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Telescope Performance and Datataking

Telescope Performance and Datataking. 2009 AUSAC Committee Meeting Phil Perillat. Talk Outline. Telescope performance Pointing Gain/Sefd/Tsys Datataking (mock pdev spectrometer) Current status and Usage. What we’ve learned. Yet to be done.

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Telescope Performance and Datataking

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  1. Telescope Performanceand Datataking 2009 AUSAC Committee Meeting Phil Perillat NAIC AUSAC Committee Meeting · March 9-10 2009

  2. Talk Outline • Telescope performance • Pointing • Gain/Sefd/Tsys • Datataking (mock pdev spectrometer) • Current status and Usage. • What we’ve learned. • Yet to be done. Online: http://www.naic.edu/~phil/talks/ausac09/xxx.ppt NAIC AUSAC Committee Meeting · March 9-10 2009

  3. Pointing • Pointing model made dec07/jan08 after painting shutdown. NAIC AUSAC Committee Meeting · March 9-10 2009

  4. Pointing: data taken jul08-feb09 • Pointing errors vs Za • Pointing errors vs Azimuth. • Error vs az looks like a platform tilt toward td12. This gives a 1 azimuth dependence of the the error . • 1 platform inch rotation at 192 ft (tdCables) is is 12.5 (za=2) to 18. (za=20) asecs. • RmsError (za,az)=(4.6,6.8) asecs. Total=8.2 asecs. • Fine for alfa/lband. Not so great for 28 asec beam of xband @ 10Ghz. NAIC AUSAC Committee Meeting · March 9-10 2009

  5. Gain,SEFD,Tsys:lband,cband • Data jul08 thru feb09. • Lband @ 1400Mhz • Cband @ 5000 Mhz • Gain • Tsys • Sefd • Beam width NAIC AUSAC Committee Meeting · March 9-10 2009

  6. Surface error • Ruze curve shows gain loss vs surface error. • Gain=G0*exp(-(4*pi*delta/lamda)^2 • Need to pick G0.. Used 10.75 K/Jy • Other factors (besides reflector error) can decrease gain: • Under illuminating tertiary (cbh) • Bad cals • Most source extended for cbh,xband. NAIC AUSAC Committee Meeting · March 9-10 2009

  7. Alfa Tsys • Alfa tsys measured during survey runs: • 1671 measurements dec08 thru feb09. • Each color is a different project: • Black:A2010 (alfalfa), Red:A2048(ages), Green:A2133(auds), Blue:(A2432) • PolA on left, polB on right. • Beams 0-3 • Beams 4-6 • Beams 3,4 at highest Za for a2010. NAIC AUSAC Committee Meeting · March 9-10 2009

  8. Mock pdev spectrometer: Status • 1 box can process: • 2*172=342 Mhz, in each of 4 pols (A,B,U,V), and 8192 channels/172Mhz spectrum. • We have 14 boxes installed in system: • 7 boxes:1/beam for primary observer • 7 boxes: 1/beam for commensal observer • We own 24 boxes. • 1 Fileserver/box (14 fileservers). Each fileserver has 4 Tbytes of disc (14*4 = 56 Tbyes total). NAIC AUSAC Committee Meeting · March 9-10 2009

  9. Current pdev projects: • G-Alfa continuum Transit survey: 33 sessions • Full stokes, 4096 channels/pol, 1 millisecond sampling with winking cal. • 65 Mb/sec per box * 7 boxes = 450 Mb/sec. A 6 hour run generates 10 Tbytes. • After each run: • Winking cal separated into calOn, calOff buffers. • Yet another fits file format (calOn,calOff buffers) • 1 file has decimated in time (.2 secs) full freq range • 2nd file has decimated in freq (1.3Mhz) • End up with 826 Gb per 6 hour run. NAIC AUSAC Committee Meeting · March 9-10 2009

  10. Current pdev projects • Alfa Ultra deep survey: 50 sessions • 8192 channels, polA,B and .1 second sampling • Pulsar search: 0 sessions: • 512 chan/172 Mhz, 65 Usec sampling, add pols. • 32 Mb/sec per box. 220 Mb/sec for 7 beams. • 3 hour session= 2.4 Tbyes/3hr session. With observing efficiency of 80% this is about 2 Tbytes. NAIC AUSAC Committee Meeting · March 9-10 2009

  11. Current pdev projects • Pulsar search cont.. • Psrfits file format implemented • Conversion to sigproc file format done. • Runs ok by itself. Bug when running with zoa commensal observing… Need to figure it out. NAIC AUSAC Committee Meeting · March 9-10 2009

  12. Current pdev projects • Aeronomy: • 32 Mhz time domain sampling. • Tamara hall had been working on fpga code (but left) • Student at penn state now working on this • Sband radar • 32 Mhz time domain sampling • Do doppler correction in fpga. • Tamara hall had been working on this but left. Luis Quintero is the new digital engineer. NAIC AUSAC Committee Meeting · March 9-10 2009

  13. FGPA dynamic range and radars • 18 bit fixed point arithmetic in fpga. • Fft butterfly stages have mult and add. • Noise increases as sqrt(Number adds). • Every 2nd butterfly we downshift. • Coherent signals (radars) increase as N. • Every butterfly we need to downshift. • Send A/D 12 bits to upper 18 bits of register (leaves 6 bits free below). • Downshift on 1st 6+3 stages then alternate every stage. This keeps the noise from growing. • If a radar is strong enough then it can still overflow the butterflies. • First 9 stages are down shiftsfft<=512 can’t overflow. • 1024 length fft is difficult • 1024*5ns/pnt=5 usecs = pulse width of faa radar. • Every sample in fft will have the radar pulse. NAIC AUSAC Committee Meeting · March 9-10 2009

  14. A/D blanking • Clipping noise is ok, clipping a radar is like clipping a sine wave, is sends power all over the spectra. • Solution: • If a time sample hits the A/D limit, flag it as bad. • Any fft with a bad sample is not included in the accumulation. This resolution is 40 usecs for an 8k fft. • This helps the butterfly overflow problem since overflows in the butterfly usually happen with A/D signals that hit the limits. • So far everyone has decided to use this mode. This was an option that jeff mock threw in because he thought it was cool. NAIC AUSAC Committee Meeting · March 9-10 2009

  15. Complex vs real sampling • Pdev uses complex sampling • The mixer image rejection works if the I,Q amplitudes are equal and the 90 degree phase shift is met. • The radars push the mixers into saturation causing an image to appear on the other side. • Real sampling would put mixer harmonics at a higher freq. They could then be removed with a baseband filter. • Example later.. NAIC AUSAC Committee Meeting · March 9-10 2009

  16. File formats: • .pdev for time domain data (Jeff mocks origin) • cimaFits for “standard” spectral line data. • Galfacts fits for calon, caloff buffer storage. • Psrfits for the pulsar community. Used for archiving the data. • Sigproc format for the pulsar community. This is what their programs want as input. • If this continues, next year I’ll use a smaller font. NAIC AUSAC Committee Meeting · March 9-10 2009

  17. Pdev: A look at some data. • 1450 band: dynamic spectra .2 sec avg. • 1300 Mhz .2 sec avg. • No aeroStat • With Aerostat • Notes: • 1330,1350 FAA radar • 1270,1270 REMY radar • 1242,1256 aerostat • 1232/1248, 1242/1256 Punta salinas mode A • Images of radar about 1300 (complex sampling) • Radars don’t spread very far NAIC AUSAC Committee Meeting · March 9-10 2009

  18. To do.. • Fix bug so pulsar search runs with ZOA • Get single Pixel working: • 1 Ghz spectra using 7*150 Mhz bands • Partly in cima • Get Aeronomy working: • Penn state fpga code and program being tested. • Get sband running: • Needs fgpa programming (or use regular baseband sampling with pdev). NAIC AUSAC Committee Meeting · March 9-10 2009

  19. To do.. • single pixel Baseband sampling: • Need to add functionality to cima • Work on pdev headers. • Bandwidth/box: • 7 or 14 boxes.. NAIC AUSAC Committee Meeting · March 9-10 2009

  20. Summary • Pointing • Current rmsError: za: 4.6, az:6.8, tot:8.2 asecs • Ok for alfa, needs az model work for high freq. • How important is making the pointing better (with limited people) • Gain,Tsys,sefd,Tsys • Sefd: lbw: 2.6Jy, Cband : 3.2Jy • Surface error doesn’t look terrible.. But need to work on the curve.. • Tsys alfa 28-30 K • Alfa amps need leds installed for stability during radar pulses ...(ganesh). • Pdev • Galfacts, Auds running. • Pulsar search, ZOA start soon. • Alfalfa .. Stick with wapps. Ages ?? • Get single pixel working • Get aeronomy and sband working • Replace Mikael lerner…. NAIC AUSAC Committee Meeting · March 9-10 2009

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