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Telescope Performance and Datataking. 2009 Visiting 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. - PowerPoint PPT Presentation
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NAIC Visiting Committee Meeting · April 20-21 2009
Telescope Performanceand Datataking
2009 Visiting Committee MeetingPhil Perillat
NAIC Visiting Committee Meeting · April 20-21 2009
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/talks.html apr09 vc09
NAIC Visiting Committee Meeting · April 20-21 2009
Pointing
Date Az Err (arcsec)
Za Err (arcsec)
Total Err (arcsec)
1998 mod09 3.82 2.37 4.491999 mod10 5.4 3.1 6.22000 mod11 5.68 3.45 6.652003 mod14 5.38 3.48 6.412004 mod15 4.20 2.41 4.84
2007mod17 4.39 2.99 5.31
Jul08-feb09 6.8 4.6 8.2
• Pointing model made dec07/jan08 after painting shutdown.
NAIC Visiting Committee Meeting · April 20-21 2009
• 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 error .
– 1 platform inch rotation at 192 ft (tdCables) 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.
Pointing: data taken jul08-feb09
NAIC Visiting Committee Meeting · April 20-21 2009
Gain,SEFD,Tsys:lband,cband
• Data jul08 thru feb09.• Lband @ 1400Mhz• Cband @ 5000 Mhz• Gain• Tsys• Sefd• Beam width
Lband1400
Cband5000
Gain 11K/Jy 8K/Jy
Tsys 28 K 27 K
SEFD 2.6 Jy 3.3 Jy
bmWidth 204” 55”
NAIC Visiting Committee Meeting · April 20-21 2009
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 (about 75%
appeture efficiency).
Other factors (besides reflector error) can decrease gain: Under illuminating tertiary (cbh), bad cals, most sources extended for cbh,xband.
NAIC Visiting Committee Meeting · April 20-21 2009
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 Visiting Committee Meeting · April 20-21 2009
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 online).
NAIC Visiting Committee Meeting · April 20-21 2009
Current pdev projects:• G-Alfa continuum Transit survey (GALFACTS):
– 33 sessions so far.– 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.– Processing immediately 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 Visiting Committee Meeting · April 20-21 2009
Current pdev projects
• Pulsar search (PALFA)– About 15 sessions so far.– Psrfits file format used for data recording.– Convert to sigproc format for processing.– 512 chan/172 Mhz, 65 Usec sampling, add
polarizations in the spectrometer.
NAIC Visiting Committee Meeting · April 20-21 2009
Current pdev projects
• Pulsar search continued….– I/O rates:
Duty cycle Per box All Beams
100% 32 Mb/sec 220 Mb/sec
100% 113 Gb/hr 792 Gb/hr
80% 90 Gb/hr 633 Gb/hr
2hr session 180 Gb/session 1266 Gb/session
NAIC Visiting Committee Meeting · April 20-21 2009
Current pdev projects• Alfa Ultra deep survey (AUDS):60 sessions
– 8192 channels, polA,B and 1 second sampling• Zone Of Avoidance (ZOA):starting…
– 8192 channels, polA,B .1 or 1 sec sampling
NAIC Visiting Committee Meeting · April 20-21 2009
Commensal pdev usagePrimary Commensal 1 Commensal 2
Palfa pdev Zoa pdev
ALFALFA (wapps)
Galfa galspect Palfa pdev(proposed)
Igalfa galspect Zoa pdev Galfacts pdev
NAIC Visiting Committee Meeting · April 20-21 2009
Current pdev projects
• Aeronomy:– 32 Mhz time domain sampling.– Tamara hall had been working on fpga code but left.
She has now been rehired as a consultant.– Student at penn state also 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 Visiting Committee Meeting · April 20-21 2009
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 shiftsfft<=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 Visiting Committee Meeting · April 20-21 2009
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 Visiting Committee Meeting · April 20-21 2009
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 Visiting Committee Meeting · April 20-21 2009
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 Visiting Committee Meeting · April 20-21 2009
• 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
Pdev: A look at some data.
NAIC Visiting Committee Meeting · April 20-21 2009
To do..
• 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 Visiting Committee Meeting · April 20-21 2009
To do..
• single pixel Baseband sampling:– Need to add functionality to cima– Work on pdev headers.– 7 or 14 boxes..– Bandwith per box: Bits 1pol
Mhz2polMhz
4 70 358 35 17.516 17.5 8.75
NAIC Visiting Committee Meeting · April 20-21 2009
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, palfa, zoa all running.– Alfalfa .. Stick with wapps. Ages ?? – Get single pixel working– Get aeronomy and sband working
• Replace Mikael lerner….