Memo Review Memo: 423 - The Vane Calibration System Revisited Guilloteau, 2002May27 Reviewer: Jesus-Martin Pintado Date Received: 2003Feb07 Review: This memo shows the implications of the expected saturation of the ALMA receivers on the accuracy of the semi-transparent (S/T) vane calibration scheme. It is shown that achieving 1% accuracy in the calibration requires the use of two different vanes. One optimized for 86 GHz and the other for 280 GHz. The memo also shows the advantages of adding an ambient load which allows to estimate the degree of saturation of the receivers and to correct for the effects of possible saturation on the S/T vane. General comment The memo clearly shows that achieving 1% accuracy is very challenging. The memo addresses the effects of mixer saturation and its implications. For completeness, it would be useful to include other possible effects like the gain compression in the IF amplifier chain. What is the present specification for the IF gain compression?. Section 1 I am a bit confused with Fig. 1. Trec SSB is a factor of 2 larger than DSB, but (in Fig. 1) Tan (Trec+Jsky) in SSB is only 1.4 time larger than in DSB. Section 2 In page 4, it is motioned that compression in the IF chain is not considered. As mentioned before, it might be quite useful to include at least the baseline specification for the IF gain compression. Section 3 3.1 After the equations of the semitransparent vane it would be useful to define 1-f as the transmission coefficient of the vane. I suggest to suppress Fig 3 (referred in the text as Fig. 3.1 ) since it is clearly explained in the text. 3.2 It is unclear to me what on-time fraction means in Figs 4 and 5 bottom. All the calculations are made for a S/T vane absorption coefficient proportional to the frequency. However, most of the materials measured, so far, seem to show an absorption coefficient proportional to the frequency to the 1.5. It might be useful to consider also this case to specify the optimum number of S/T vanes the their transmission coefficients. Conclusions End of page 12. This is the first time that it is mentioned that the nature of the losses in the S/T vane calibration scheme might be of importance to achieve the 1% calibration accuracy. It might be interesting to mention this assumption at the beginning of section 1. It is also suggested that 1% calibration accuracy in Band 7 is difficult to achieve. Since this has important implications it might also appears in the Abstract. Minor Last line in Page 2 say "measure by the correlator" -> "measure on the source by the correlator" Fig2. figure caption "function for frequency" -> "function of frequency"