Project Echo: The Dual Channel 2390-mc Traveling-Wave Maser

* Although this equipment was designed by the Bell System as part of its research and development program, it was operated in connection with Project Echo under Contract NASW-110 for the National Aeronautics and Space Administration. 1117 1118 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1961 amplifier for the signal channel. The other maser served as a preamplifier for a monitoring channel which received data on the imperfections of the transmission path. The system used frequency modulation. It required a receiving bandwidth of approximately 1 mc centered at 2390 mc for the signal. A slightly wider bandwidth was required, however, since continuous skynoise monitoring was desired at 2388 mc; this frequency was outside but close to the signal channel. Further receiving system details are given in the accompanying paper by Ohm. 3 The system objective called for masers with the following requirements: 1. two identical amplifiers for duplex operation; 2. lowest possible noise temperature; 3. bandwidth greater than 3 mc; 4. long-term gain stability; 5. at least 33 db gain; (). dynamic range greater than 60 db; 7. sufficient running time between helium transfers to permit operation for a full sequence of neighboring satellite passes; 8. center frequency 2390 mc. Because of items 2, 4, and 6, it was decided that traveling-wave masers would be the most desirable. It was shown previously that these general objectives could be met at 6 kmc. Apart from the frequency, the main differences were the requirement for a higher gain and no electronic tuning.