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This paper presents an analysis of instantaneous frequency scaling of scintillation using propagation data recorded during a three month period (May-July 1997) at Sparsholt UK from the ITALSAT satellite beacons at frequencies 18.7, 39.6, and 49.5 GHz. Variations in the height of turbulence within reasonable limits were found to have a negligible effect on the scaling ratios. Furthermore, the exponent in the power law dependence of scintillation intensity on signal frequency was found to be on average 27% smaller than the theoretical value of 7/12 and to exhibit a slight diurnal effect. It is shown that this behavior can be partly accounted for by receiver thermal noise contribution to the measured signal variance. Ascribing the minimum observed short-term variance in each beacon to thermal noise and excluding this contribution yielded a higher exponent, which was nevertheless 15% below the theoretical value.