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Additional info for Astrophysics,Part C, Radio Observations (Methods of Experimental Physics)
Univ. (1970)]. The time and intensity scales are shown for both records. 13b) Then, if the variation in the background is linear, we can set background and the net result is = background east + background west 2 - signal = 2 source. 13~) Thus, because one beam is always on-source, the signal-to-noise ratio is twice that of an ordinary on-off measurement. This technique can also be used with the scanning procedure by directing the scan along the axis between the two beams. The recorded signal will first deflect one direction and then the other, with the maximum difference between twice the single-beam antenna temperature as shown in Fig.
Of the various forms of switching, the frequency switch is used extensively because of the ease with which good baselines can be obtained. Frequency switching has the principal advantage that the comparison window off the line has the same underlying continuum temperature as the spectral region of the line. The system is thus automatically balanced. In addition, there is a cancellation of some of the curvature that is inherent in the baseline. The technique of switching against a load or horn pointed toward the sky also plays an important role in spectral-line work.
R. Dickel, Zcarus 6, 417 (1967)l. 11 12 4. SINGLE-ANTENNA OBSERVATIONS record shown is the difference output from the switched radiometer and represents the signal received in the feed at the indicated position angle P A minus that in the feed at P A 90". 5% at a position angle of 180" is detectable on the records. The instrumental effect is apparently caused by distortions of the dish surface which slightly alter the amount of power reflected at different position angles. That there is not a different response in the two feed systems can be verified by making switched-polarization observations at two indicated position angles separated by 90%.