Technikatörténeti szemle 8. (1975-76)

TANULMÁNYOK - Vajda P.–White, J. A.: Bay Zoltán úttörő Hold-radar kísérletének harmincadik évfordulója és a korszerű radar csillagászat

The present article points out on the 30th anniversary of the two experiments that, by the use of long time integration techniques, the experimental design of Bay went one step further in the direction which was followed later on by modern radar astronomy. In order to improve the originally poor signal to noise ratio provided by his equipment, Bay devised a novel method for long range radar which has been used in all subsequent, modern radar astronomy systems. This method consists of repeating the experiments a large number of times, of preserving the feeble echo amplitudes undiminished in strength for the entire duration of the experiments, and of summing the amplitudes and raising thereby the signal above the statistical sum of the noise amplitudes. In the case of integrating n pulses the sum of the signals is n times the individual echo amplitudes while the noise increases only "Jn . Thus the resulting signal to noise ratio is fn times that of the receiver output for individual pulses. Bay applied a bank of water voltameters (coulometers) connected by a rotary switch to the output of the receiver. The integration of about a thousand pulses resulted in an about 30 fold increase in the signal to noise ratio and raised the resulting signal above the noise level. Bay closed his paper reporting his results in 1946 with the remark that in future experiments, extended to other celestial objects too, the best results would be yielded by a combination of highly developed microwave techniques with the method of integration. This expectations of Bay were fulfilled in the development of modern radar astronomy. Discussing the tremendous increases in sensitivity achieved by integration techniques in radar astronomy, A.G.Smith and T.D.Carr say in their book (14) on . page 123: "The unique method devised by Bay in his pioneer lunar radar investigations is an example of such a technique." There is every expectation that future radar astronomy systems will continue to use the long time integration techniques pioneered by Bay in Hungary in his lunar radar work reported in 1946.