NAIC AUSAC Committee Meeting · March 9-10 2009 Telescope Performance and Datataking 2009 AUSAC Committee Meeting Phil Perillat

NAIC AUSAC Committee Meeting · March 9-10 2009

Telescope Performanceand 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.

Online: http://www.naic.edu/~phil/talks/ausac09/xxx.ppt


Pointing

Date Az Err

(arcsec)

Za Err

(arcsec)Total Err (arcsec)

1998 mod09 3.82 2.37 4.49

1999 mod10 5.4 3.1 6.2

2000 mod11 5.68 3.45 6.65

2003 mod14 5.38 3.48 6.41

2004 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.


• 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.

Pointing: data taken jul08-feb09


Gain,SEFD,Tsys:lband,cband

• Data jul08 thru feb09.• Lband @ 1400Mhz• Cband @ 5000 Mhz• Gain• Tsys• Sefd• Beam width

Lband

1400

Cband

5000

Gain 11K/Jy 8K/Jy

Tsys 28 K 27 K

SEFD 2.6 Jy 3.3 Jy

bmWidth 204” 55”


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.


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.


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).


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.


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.



• 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.



• 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.


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.


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.


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..


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.


• 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.


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).


To do..

• single pixel Baseband sampling:– Need to add functionality to cima

– Work on pdev headers.

– Bandwidth/box:

– 7 or 14 boxes.. Bits 1pol

Mhz

2pol

Mhz

4 70 35

8 35 17.5

16 17.5 8.75


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….

Documents

NAIC AUSAC Committee Meeting · March 9-10 2009 Telescope Performance and Datataking 2009 AUSAC Committee Meeting Phil Perillat