Note on Day-to-Day Variations in Sensitivity of a Broadcast Receiver

A series of sensitivity measurements on a highly sensitive broadcast receiver over a period of one month indicates that large variations in sensitivity may occur. The importance of these variations in sensitivity is pointed out with particular reference to intercomparison of receiver measuring equipment and production testing of radio receivers. In this particular study, a high degree of correlation between relative humidity and sensitivity was found; i.e., days of high relative humidity were also days of low sensitivity and vice versa. This effect is probably attributable to increased losses in the radio-frequency transformers during periods of high relative humidity. It is shown that changes in sensitivity may be delayed as much as four days after the corresponding changes in relative humidity.