David C Hogg Early lownoise and related studies at Bell Laboratories Holmdel NJ

The US National Academy of Engineering cites Hogg's election to the Academy for his "contributions to the understanding of electromagnetic propagation at microwave frequencies through the atmosphere." A native of Saskatchewan, Hogg's current interest is the composition of music.

A giant in radio science, Harald T. Friis1 was head of the Bell Radio Research Laboratory in Holmdel. Having pioneered work on the superheterodyne receiver in the late 1920s, he played a key role in Karl Jansky's initial experiments and the beginning of radio astronomy in the early 1930s. His interests then turned to shorter wavelengths which eventually led to the construction of a nationwide microwave radio-relay system employing "horn-reflector" antennas that he patented with Al Beck. This antenna design is highly efficient and was used in all of the low-noise microwave systems to be discussed here. These remarks are made to indicate that high-quality equipment, designed for very practical purposes, can be used as a tool for first-class science. It is to the credit of the United States that the AT&T Bell Laboratories existed, allowing such broadminded interactive research to be done.

In the 1950s, not long after John R. Pierce had traveled to the UK, including Oxford, he brought Rudi Kompfner to Bell Labs. They asked me to calculate the thermal noise from the Earth's atmosphere over the microwave band. This noise level was needed for their calculation of the feasibility of microwave communication by reflection from an orbiting balloon (Pierce and Kompfner 1959). It was fortunate that some time earlier, with Arthur B. Crawford, I had measured the millimeter-wave absorption by the oxygen and water vapor in the sea-level atmosphere (Crawford and Hogg 1956). Thus the broadening constants for computation of "sky noise" were determined and that calculation was completed (Hogg 1959).

However, no sky noise measurements were available to corroborate this theory. Nevertheless, again fortunately, at that time Derek Scovil and Bob De Grasse at the Bell Laboratory, Murray Hill, NJ, were well along in developing microwave traveling wave solid state masers (TWM), with noise temperatures on the order 10 K (De Grasse, Shulz-Du-Bois and Scovil 1959). Again encouraged by Kompfner and Pierce, we, therefore, combined this maser and antenna to produce a "low-noise" receiving system.

1 This is a good occasion to remind the reader that the Glossary is meant to serve as a guide, in this case to Friis' interview of Burke (p. 177) and to Friis' influence on the development of the technology that detected the fossil microwave radiation (pp. 159 and 162).

Here we discuss and compare three systems at various microwave frequencies, with emphasis on the technology and low-noise results that pointed the way toward a determination of the microwave cosmic background noise. In all three cases, the equipment was designed and built to demonstrate the feasibility of satellite communications, and the cooperation of NASA and the Bell Laboratories System Department were important factors.

The first low-noise microwave system (De Grasse et al. 1959) operated at 5.65 GHz. The antenna mount, constructed of wood, on the lip of Crawford Hill, allowed manual beam pointing in elevation only; a photograph is shown in Figure 4.1. The rectangular waveguide input to the TWM was fed via a rotating joint in the circular waveguide from the antenna. The output from the TWM preamplifier was then fed to a conventional superheterodyne. This combination resulted in a (zenith) system noise temperature of 18.5 K.

At that time I was invited by John Shakeshaft to Cambridge, England, and gave these results in Maxwell's lecture room at the Old Cavendish. A seminar also was given at the old McDonald physics building at McGill University, Montreal, Canada, where Ernest Rutherford did research on the alpha particle and helium.

Although this system was unsophisticated, it did serve as a prototype for the following two systems that were used for actual communications via satellites: Echo and Telstar.

The second low-noise microwave system (Ohm 1961) was designed and built specifically for the Echo satellite project at a frequency of 2.39 GHz, for receiving signals reflected from an orbiting balloon. The receiver design was engineered by Ed A. Ohm and the project engineer was W.C. (Bill) Jakes Jr. The antenna (Crawford, Hogg and Hunt 1961), a 20-ft aperture horn-reflector, is shown in Figure 4.2; design and construction was managed

Fig. 4.1. The antenna in the first low-noise microwave system.

Fig. 4.2. Horn-reflector antenna used in the Project Echo experiment.

Table 4.1. Summary of satellite communication systems

Experimental communication system

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