sentences:  These papers documented studies of field strength and noise over a wide range of frequencies and stressed the importance of the signal to noise ratio (SNR) in receivers rather than simple field strength.During the early 1930s Friis helped design the radio receiver used by Karl Jansky for radio astronomy, and with Edmond Bruce invented the rhombic antenna widely used for shortwave communications.In 1938 Friis became the director of the Holmdel Radio Laboratory developing microwave systems, where he and Alfred C. Beck designed the horn reflector antenna, which was widely used in AT&T's national microwave relay network in the 1960s.