Project Echo: Receiving System

By using large antennas and a high-powered transmitter, it was calculated that a modest carrier could be received in New Jersey from California via the Echo I satellite. 1 In order to establish a good voice circuit with this carrier, it was clear that the effects of noise had to be reduced by using a very-low-noise receiver. It was also clear that a special demodulator, which featured FM with negative feedback, 2 could reduce the noise effects still further. Although a parametric amplifier in combination with this type of demodulator would yield a good voice circuit under near-ideal conditions, a maser would allow a circuit with a more practical carrier-to-noise margin.* In this regard, a previous experiment had demonstrated that an ultra-low-noise system temperature could be achieved in practice by using a low-noise horn-reflector antenna in combination with a traveling-wave solid state maser. 3 In accordance with these preliminary results, a larger horn-reflector tracking antenna was combined with two traveling-wave masers or alternately two "standby" parametric amplifiers to provide two separate low-noise systems, one for each sense of circular polarization. Special FM demodulators were used to achieve voice circuits of excellent quality from the resulting modest * It is i m p o r t a n t to m a i n t a i n some m a r g i n ; otherwise, at a critical carrier-tonoise r a t i o a s m a l l d e c r e a s e in c a r r i e r or i n c r e a s e in noise will c h a n g e t h e voice c i r c u i t f r o m o n e t h a t s o u n d s good t o one t h a t i s c o m p l e t e l y u n i n t e l l i g i b l e .