An experimental study of atmospheric optical transmission

Measurements are presented for an atmospheric optical transmission link, covering 23 miles, that is to be used as a standby substitute for microwave radio undergoing severe multipath or obstruction fading. The comparative measurements involve a microwave system at 11 GHz capable of frequency-selecting fading, and an optical system at 6328 A which allowed amplitude changes of the received optical signal to be obtained. On the single occasion when frequency-selective microwave fading was observed, there was no optical signal fading. It was found necessary to control the transmitter elevation angle with a servo error signal from the receiver. The optical beam can be automatically reacquired after severe atmospheric attenuation.