Microwave sky noise

A sensitive microwave receiver capable of measuring small differences of radiant energy in the 3000‐Mc band has been constructed after the manner of Dicke [see 1 of “References” at end of paper], and is used to measure the radio noise from the sky at Ottawa, Canada. A continuous record is obtained by means of a recording milliammeter. The receiver is calibrated by measuring the temperature of a resistance which has been substituted for the antenna; thus the equivalent temperature of the sky is used as a measure of the sky noise. The records taken during the period April 30 to July 23, 1946, were interrupted to make improvements in the receiver, and by occasional failure of the set. During this period, an antenna with a cone of acceptance of 30° to the half‐power points was used. After July 27, a continuous record was taken using an antenna with an acceptance cone of 6°. In each case the antenna was pointed toward the zenith with the electric vector in the magnetic east‐west direction. The narrow‐beam antenna is astronomically mounted so that solar noise observations can be taken; when this antenna points more than 15° away from the Sun, no solar noise can be received, and the background noise is measured independently.