polA ripples 30sep10
A2524 used double position switching (dps) with the
800 MHz rcvr on 30sep10. Their setup was:
- 800 MHz rcvr
- mock spectrometer using 5 bands with bandwidths:172,57,28,14,7
- center freq changed for different sources
- 1 sec integrations. 300 seconds on,off source, 60 secs on,off
calibrate, and cal on,off.
- I used the 172Mhz band limiting data to 700-800 Mhz.
Looking at the data for J001018+1433
for the 300 off spectra:
Double position switched data (.ps) (.pdf)
spectra and frequency content of bandpass ripple (.ps) (.pdf)
- Top: SourceDif and Calibrator diff (both normalized to unity
across the band).
- black polA source, red polB Source. Green is the pola, polB for
- You can see jumps in the polA source difference (black).
- 2nd: (srcOn-srcOff)/(calibOn-calibOff)
- black is pola, red is polb.
- The ripples in polA stick out.
- 3rd: standard (on-off)/off processing for source
- 4th: standard (on-off)/off processing for calibrator.
- Note that the 20 MHz ripple is not cancelled by the on,off
position switch on the strong calibrator.
- Page 1: average bandpass for 300 seconds off source.
- Page 2: frequency content of bandpass ripple and how it changes.
- the 300 seconds of data was split into 5 60 second averge
- the 1st average spectra was then divided into minutes 2..5.
- the fft was then computed for these 4 spectra:
- This is the acf of the spectra
- The data is plotted vs delay in usecs.
- Top PolA, bottom polB
- black is minute 2, red=minute3, green=minute4, blue minute 4.
- the spike at 1 usecs is the 1 mhz standing wave dish to
- polA shows the 1 usec spike, polB doesn't.
- For the 1 usec spike to appear, the standing wave phase must
change its phase.
- If the phase was constant, then dividing by the first minute
should cancel it.
- After double position switch processing, polA baseline is
worse than polB
- The 20 MHz bandpass ripple does not cancel on on/off processing
if the on is a strong source.
- PolA has 1 MHz ripple that doesn't cancel over a 5 minute
integration. polB is more stable.
- I processes a second source. It also showed ripple in polA