SEST - System Performance
Allan Variance

The gain stability is measured to find the maximum integration time inherit to the system (that is the spectrometers in combination with the receivers) for which the noise decreases (cf. A in Fig. below). After a short plateau, where the noise level stays stable (B), the noise will then start to increase (C) again due to system instabilities (flicker noise). However, under normal observing conditions, the sky noise level is above this system noise, thus longer integration times will be useful up to a given maximum integration time. Experience has shown this time to be no more than 240 seconds under perfect observing conditions.



The gain stability is measured on only three of our spectral line receivers (RX100, RX150 and RX345) in combination with the HRS. The results indicate a maximum integration time of the order of 30 seconds for the 100 GHz and the 150 GHz receivers, and 10 seconds for the 345 GHz receiver. In the following table, the results for RX100, RX150 and RX345 are presented based on the last measurements during 1995. Measurements for RX115 and RX230 are expected to be available very soon:

 

Receiver

Frequency (GHz)

Maximum Integration Time [s]

RX100

86

25

RX115

n.a.

n.a.

RX150

147

29

RX230

n.a.

n.a.

RX345

345

11.5

 

Last modified by Felipe Mac-Auliffe, July 23rd 2001
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