are from 60 db to 90 db below the carrier. Measurements made at JPL on radiation at harmonic frequencies from a slotted waveguide array indicate that the power density of harmonics is down by another 50 to 60 db. hi addition, low pass filtering can be used in the magnetron to additionally reduce the harmonics so that it appears possible to meet the CCIR requirements at the harmonic frequencies Phase Locked, High Gain Amplification from the Magnetron Directional Amplifier It has long been known that an oscillator can be locked to an external frequency source of greatly' reduced power level The locked oscillator can therefore be made to appear as an amplifier. However, if it is desired to always make the phase of the amplified output power equal to the phase of the lower level power to which the oscillator is locked, it is necessary to tune the frequency of the oscillator to the same frequency as that of the driver. This can be accomplished by comparing the phase of the output with the phase of the input and using any difference to tune the magnetron in some way to compensate for other factors that will also change the frequency, such as changing the output amplitude of the tube, the temperature of the tube, etc. In performing this tuning, it is desirable (and sometimes necessary) to be able to have independent control of the output power level of the tube from the frequency of operation. This independent control had not been accomplished until recently when a development supported by both the Center for Space Power at Texas A&M and the author did accomplish it. This independent control for 30 db power gain is shown in Figure 6. It is anticipated that with additional refinement 40 db of gain can be obtained. This independent control is considered to be necessary for most wireless power transmission applications where it is anticipated that there will be a precise frequency assigned to wireless power transmission applications, very similar to the 60 Hertz frequency assigned to wire systems. This will facilitate the use of rejection filters in Figure 8-6 Magnetron Performance Envelope communication receivers to reject the frequency used for power beaming Figure 7 compares the operation of the magnetron directional amplifier with that of the conventional frequency locked magnetron. Long Life Prediction for the Space Based Magnetron in the SPS. When NASA simultaneously indicated an interest in the use of the MDA (magnetron directional amplifier) in the SPS and a concern for the life of the magnetron in the MDA, the author at Raytheon carried out a detailed investigation program, using the microwave oven magnetron as the experimental vehicle. Making use of these experimental findings and the extensive literature on the theory and experimentally observed life performance of carburized thoriated tungsten cathodes [4], a tube for the SPS transmitter was designed to have a life expectancy of 50 years, as described in Appendix A. [2]
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