Determination of the Follow-up Receiver Noise-Temperature Contribution
Tom Y. Otoshi · 2000
This article presents the derivations of both the exact and approximate equa-tions for determining the follow-up receiver noise temperature from measured output powers when the flrst-stage low-noise amplifler (LNA) power supply is turned on and ofi. Although approximate equations have been used by DSN engineers since the early 1960s when the LNA was a maser, it is important to know whether the equation and experimental procedure are still valid when the LNA is a cryogenically cooled high-electron mobility transistor (HEMT) rather than a maser. In this arti-cle, it is shown that the approximate equations and experimental procedure being used for masers can also be used for HEMTs for obtaining an accurate value of the follow-up receiver temperature. However, if the flrst stage amplifler is not cryo-genically cooled, but is at room temperature, it is shown that, if the approximate equation is used, a correction factor (also derived in this article) might have to be applied in order to get an accurate value. Since the derivations do not appear to be documented in any reports, the equations are rederived and presented in this article. I.