10.1 NOISE CONSIDERATIONS 10. 1.1 AMPLITRON Discussing the amplitron first and utilizing the information in Section 4, Figure 4-45, we see that a ten tube amplifier chain has a noise power which is 70. 1 dB/MHz below the power at the fundamental transmitted frequency (fQ)» This translates to -130. 1 dB/Hz. The noise spectrum has been described as essentially flat over a bandwidth of approximately 500 MHz above the center frequency, and noise shaping is shown in Figure 4-53. The noise power is going to have an effective gain from the transmitting antenna which depends on the area over which the noise is coherent. If we consider 10 converters in series the noise will be essentially determined by the first tube. Therefore a high coherency factor will be maintained over the area taken up by that set of 10. The total power per set is then 5 kW x 10 or 50 kW. Since a total of about 7 GW will be generated at f (for 5 GW ground output power), there will be 1.4 x 105 such sets. The transmitting antenna has a radius of about 500 meters and therefore has an area of On the average, each set of 10 tubes will then take up an area of about The factor of 0. 5 is inserted as an approximation to the coherency factor.
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