How to measure the stability of the receivers

CK 21-Jan-2012 (1st version: 15-Sep-2010)

The idea is to "observe" the hot load taking data over at least an hour and at a rate of about 0.5seconds. This allows to monitor the stability of the entire receiver/IF-distribution/backend chain. Such observations should be done on any of the receivers and with the continuum backends connected to measure the total power stability, but also with the spectrometers (e.g. the FTS) connected to measure the spectroscopic stability. The instrumental drifts are characterized by an Allan-variance analysis, by binning the data in bins of increasing integration time and finally plotting the variance versus integration time. For pure white noise, the noise will drop with T**-0.5. However, at some point drifts will start to dominate and the curve will deviate from the -0.5 slope. (References: e.g. Roelfsema et al. 2012, A&A, 537, A17; Ossenkopf et al. 2008; Schieder & Kramer 2001.)

Observing the absorber

The procedures lie on:

Data reduction


Routines were originally written by HW.

Create Allan-Stability plot of continuum scan:
greg @ plotAllanCK no 20100822s227 CONTI 
this routines runs a fortran program to calculate the allan variances against
time, outputs the data to allan.dat and then plots them.

Each line in the input file allan.dat corresponds one variance point.
Each column corresponds to a frequency. For continuum observations this
can be the 4 4GHz IF channels. 

Create Allan-Stability plot of WILMA scan:
greg @ plotAllanCK no 20100823s72 WILMA 1 11 21 31 41
1 corresponds to the backend part.
11 21 31 41 are the channel numbers to be used for the calculations. These
should not be consecutive channels, to avoid any correlation between channels.

HowToMeasureStabilities (last edited 2012-01-21 12:15:26 by lt-ck)