This paper discusses the total power radiometers in the propagation experiment at
Virginia Tech using the OLYMPUS communications satellite. The experiment is set up to
measure the received signal strength of beacons at 12.502, 19.770 and 29.656 GHz on board the
OL YMPUS satellite in order to gather space-earth propagation statistics for a period of one
year. The radiometers are used to set the clear sky reference levels for the beacon receivers.
The paper begins with an overview of radio signal attenuation mechanisms, and a general
discussion of radiometry. A description of the OLYMPUS radiometers follows, with sections on
calibration techniques and the methods required to convert radiometer data into derived path
attenuation for use in setting the clear air reference levels for the beacon receivers.
Several novel techniques were used in the Virginia Tech radiometers including the use of
voltage to frequency converters for integration purposes, and reference load calibration using a
waveguide switch to swap the radiometer input from the antenna to a waveguide load of known
and stable temperature. The penultimate chapter contains data recorded in the course of the
experiment which was selected at random from the month of January 1991. The data is
compared to corresponding free space beacon attenuation data and shows conclusively that the
total power radiometer can produce highly accurate and stable attenuation measurements for
extended periods of time.
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