1. Telescope Performance and Datataking
2009 AUSAC Committee Meeting
Phil Perillat
NAIC AUSAC Committee Meeting · March

2. Talk Outline Telescope performance Datataking (mock pdev spectrometer)
Pointing
Gain/Sefd/Tsys
Datataking (mock pdev spectrometer)
Current status and Usage.
What we’ve learned.
Yet to be done.
Online:
NAIC AUSAC Committee Meeting · March

3. Pointing Date Az Err (arcsec) Za Err Total Err (arcsec)
Pointing model made dec07/jan08 after painting shutdown.
Date
Az Err
(arcsec)
Za Err
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
NAIC AUSAC Committee Meeting · March

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 10Ghz.
NAIC AUSAC Committee Meeting · March

5. Gain,SEFD,Tsys:lband,cband
Data jul08 thru feb09.
1400Mhz
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”
NAIC AUSAC Committee Meeting · March

6. Surface error Ruze curve shows gain loss vs surface error.
Gain=G0*exp(-(4*pi*delta/lamda)^2
Need to pick G0.. Used 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

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

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. 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

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

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

12. Current pdev projects Aeronomy: Sband radar
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

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

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

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

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

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

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

19. To do.. single pixel Baseband sampling: Bits 1pol Mhz 2pol 4 70 35 8
Need to add functionality to cima
Work on pdev headers.
Bandwidth/box:
7 or 14 boxes..
Bits
1pol
Mhz
2pol 4 70 35 8
17.5 16
8.75
NAIC AUSAC Committee Meeting · March

20. Summary Pointing Gain,Tsys,sefd,Tsys Pdev Replace Mikael lerner….
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 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