A Measurement of the Cosmic Microwave Background Temperature at 7.5 GHz

We have measured the temperature of the cosmic microwave background (CMB) radiation at a frequency of 7.5 GHz (4 cm wavelength), obtaining a brightness temperature of T_CMB_ = 2.70+/- 0.08 K (68% confidence level). The measurement was made from a site near the geographical South Pole during the austral spring of 1989 and was part of an international collaboration to measure the CMB spectrum at low frequencies with a variety of radiometers from several different sites. This recent result is in agreement with our 1988 measurement at the same frequency, which was made from a different site with significantly different systematic errors. The combined result of the 1988 and 1989 measurements is 2.64 +/- 0.06 K.