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Analysis of Q Band Lab Tests done in 2006

This page presents the results of the spectral baseline tests done using the Lab Spectrometer in the summer and early fall of 2006. The data analyzed are available at /home/labdata, and the logs are available at SpectralBaselinesObsLogs.

The specific datasets I used are:

The resulting figures are attached below the description of the analysis and the summary of results.

Procedures

Each run in the lab was analyzed with programs written in GBTIDL. The goal was to look at the RMS as a function of integration time and to see how it compared with theoretical predictions. In other words, does the noise decrease as the square root of time. To do this every pair of scans (e.g. 1 and 2, 3 and 4, etc.) was combined as if it were an on-off pair. A third order baseline was fit to the inner 600 MHz of the 800 MHz band, and the RMS noise was calculated for this combined pair in bands of 50, 200, and 600 MHz. The individual pairs were then accumulated and the noise in the same bands of the integrated spectrum was calculated. This is done by the program 'rms_qband.pro' (attached below). The resulting noise measurements for the individual pairs are normalized by the average noise of all pairs. The integrated noise is normalized by the average noise divided by the square root on the number of pairs. The resulting plots of the final integrated spectrum and the RMS noise as a function of scan number are attached below.

For comparison, there are also synthetic RMS calculations attached. In this case, I constructed an 800 MHz spectrum with pure Gaussian noise (generated from a random number generator). The individual spectra are accumulated and the RMS noise is calculated for the integrated spectrum. The results from this excercise are attached as well.

Results

The analysis was carried out on two datasets taken pre-upgrade, when the receiver still had the old LNAs (TQRX09MAY06 & TQRX23JUN06), and with five different tests using the new LNAs, post-upgrade. While the final baseline shapes look fairly flat for the pre-upgrade receiver, the noise in the integrated spectra do not decrease as fast as expected. Occasionally, there are large jumps in the integrated noise presumably due to the presence of intermittent baseline ripples.

Post-upgrade things are vastly improved. The noise does not always decrease with SQRT(time) for all bandwidths, but tends to perform within 10% of theory for the 50 MHz and the 200 MHz bands for most feeds. After the last LNA swap (in Oct. 2006), the noise performance was within 10% of theory for all bands and all feeds, except the L2 feed. There is significant baseline structure in the final spectrum from this feed; a higher order baseline fit may rectify this problem.

These results are particularly impressive when compared with the results from analyzing synthetic spectra. The pure random walk will produce excursions as large as 30% from theory in the integrated noise. These will damp out over long times, but we should not expect the receiver to do any better than this.

Finally, I also looked at waterfall plots for the feeds on some of the post-upgrade runs. These waterfall plots show pairs as on-off scans (e.g. 1 and 2, 3 and 4, etc.). There was no evidence of the intermittent baseline ripples that were a problem in the past. I have attached the plots from TQRX09OCT06 and TQRX10OCT06 for the four feeds.

-- DjPisano - 21 Nov 2006

Attachment: sort Action: Size: Date: Who: Comment:
rms_spec_09MAY06_L1_b3.ps action 54112 21 Nov 2006 - 19:46 DjPisano  
rms_09MAY06_L1_b3.ps action 38482 21 Nov 2006 - 19:46 DjPisano  
rms_spec_09MAY06_L2_b3.ps action 53895 21 Nov 2006 - 19:47 DjPisano  
rms_09MAY06_L2_b3.ps action 39414 21 Nov 2006 - 19:47 DjPisano  
rms_spec_09MAY06_R1_b3.ps action 53585 21 Nov 2006 - 19:48 DjPisano  
rms_09MAY06_R1_b3.ps action 37880 21 Nov 2006 - 19:49 DjPisano  
rms_spec_09MAY06_R2_b3.ps action 53688 21 Nov 2006 - 19:49 DjPisano  
rms_09MAY06_R2_b3.ps action 38611 21 Nov 2006 - 19:49 DjPisano  
rms_spec_09OCT06_L1_b3.ps action 53120 06 Dec 2006 - 15:58 DjPisano  
rms_09OCT06_L1_b3.ps action 51617 06 Dec 2006 - 15:59 DjPisano  
rms_spec_10OCT06_L2_b3.ps action 51963 06 Dec 2006 - 15:59 DjPisano  
rms_10OCT06_L2_b3.ps action 49248 06 Dec 2006 - 16:00 DjPisano  
rms_spec_10OCT06_R1_b3.ps action 53594 06 Dec 2006 - 16:00 DjPisano  
rms_10OCT06_R1_b3.ps action 51247 06 Dec 2006 - 16:01 DjPisano  
rms_spec_10OCT06_R2_b3.ps action 53856 06 Dec 2006 - 16:02 DjPisano  
rms_10OCT06_R2_b3.ps action 51448 06 Dec 2006 - 16:02 DjPisano  
rms_spec_11OCT06_R2_b3.ps action 52756 06 Dec 2006 - 16:04 DjPisano  
rms_11OCT06_R2_b3.ps action 147541 06 Dec 2006 - 16:04 DjPisano  
rms_spec_12OCT06_R2_b3.ps action 52952 06 Dec 2006 - 16:04 DjPisano  
rms_12OCT06_R2_b3.ps action 73797 06 Dec 2006 - 16:05 DjPisano  
rms_spec_23JUN06_L1_b3.ps action 57053 06 Dec 2006 - 16:05 DjPisano  
rms_23JUN06_L1_b3.ps action 33572 06 Dec 2006 - 16:05 DjPisano  
rms_spec_23JUN06_L2_b3.ps action 55986 06 Dec 2006 - 16:06 DjPisano  
rms_23JUN06_L2_b3.ps action 32820 06 Dec 2006 - 16:06 DjPisano  
rms_spec_23JUN06_R1_b3.ps action 54855 06 Dec 2006 - 16:06 DjPisano  
rms_23JUN06_R1_b3.ps action 38839 06 Dec 2006 - 16:06 DjPisano  
rms_spec_23JUN06_R2_b3.ps action 56881 06 Dec 2006 - 16:07 DjPisano  
rms_23JUN06_R2_b3.ps action 38348 06 Dec 2006 - 16:07 DjPisano  
rms_spec_15SEP06_L1_b3.ps action 55017 06 Dec 2006 - 16:08 DjPisano  
rms_15SEP06_L1_b3.ps action 49188 06 Dec 2006 - 16:08 DjPisano  
rms_spec_15SEP06_L2_b3.ps action 54620 06 Dec 2006 - 16:08 DjPisano  
rms_15SEP06_L2_b3.ps action 50210 06 Dec 2006 - 16:09 DjPisano  
rms_spec_15SEP06_R1_b3.ps action 55318 06 Dec 2006 - 16:09 DjPisano  
rms_15SEP06_R1_b3.ps action 50444 06 Dec 2006 - 16:09 DjPisano  
rms_spec_15SEP06_R2_b3.ps action 57243 06 Dec 2006 - 16:09 DjPisano  
rms_15SEP06_R2_b3.ps action 56473 06 Dec 2006 - 16:09 DjPisano  
rms_spec_23SEP06_L1_b3.ps action 52871 06 Dec 2006 - 16:10 DjPisano  
rms_23SEP06_L1_b3.ps action 50341 06 Dec 2006 - 16:10 DjPisano  
rms_spec_23SEP06_L2_b3.ps action 52968 06 Dec 2006 - 16:10 DjPisano  
rms_23SEP06_L2_b3.ps action 51657 06 Dec 2006 - 16:10 DjPisano  
rms_spec_23SEP06_R1_b3.ps action 53532 06 Dec 2006 - 16:11 DjPisano  
rms_23SEP06_R1_b3.ps action 51218 06 Dec 2006 - 16:11 DjPisano  
rms_spec_23SEP06_R2_b3.ps action 52510 06 Dec 2006 - 16:11 DjPisano  
rms_23SEP06_R2_b3.ps action 51435 06 Dec 2006 - 16:11 DjPisano  
synspec100.ps action 43329 06 Dec 2006 - 16:12 DjPisano  
synspec1000.ps action 38511 06 Dec 2006 - 16:12 DjPisano  
rms_qband.pro action 5089 06 Dec 2006 - 16:14 DjPisano  
synthetic_qband.pro action 2072 06 Dec 2006 - 16:14 DjPisano  
waterfall_qband.pro action 2105 06 Dec 2006 - 19:48 DjPisano  
TQRX09OCT06_waterfall_L1.ps action 475110 06 Dec 2006 - 19:57 DjPisano  
TQRX10OCT06_waterfall_L2.ps action 475264 06 Dec 2006 - 19:58 DjPisano  
TQRX10OCT06_waterfall_R1.ps action 475511 06 Dec 2006 - 19:59 DjPisano  
TQRX10OCT06_waterfall_R2.ps action 476298 06 Dec 2006 - 20:00 DjPisano  

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