4. 3 SYSTEM CONSIDERATIONS There are certain properties of the amplitron and the klystron important to their application in a complex, multiple installation such as the MPTS transmitting antenna. The thermal interface is covered in the transmitting antenna section. Topics described here concern efficiency, noise, phase error, failure modes and waveguide losses. 4. 3. 1 AMPLITRON GAIN AND EFFICIENCY The amplitron is basically a saturated amplifier, i. e. , an amplifier in which the rf output is essentially independent of the rf input. In addition, it is also a low gain device, so that the rf input can be a significant part of the output power. Because of this, the concepts of gain and efficiency, when applied to the amplitron, are subject to a slightly different formulation than is generally considered to be standard. With the provision that the rf input is sufficient to achieve device operating stability, the power generated is independent of the rf power input. In this context, the amplitron can be viewed as a power adder, and when this concept is related to gain, it always exhibits minimum gain of one. From Figure 4-37 we see that the rf drive power, , is a component in both the input and output of the tube. This is true even when the Equation (1) is equal to zero. Thus, the amplitron has a minimum gain of one, and is frequently used in this manner, generally referred to as the feed through mode. In the second term of Equation independent terms (once P^ is greater than a threshold necessary to lock operation) and either term can be varied independently of the other. Therefore, a given amplitron is not a fixed gain device, but will operate at different gains, depending upon the ratio of power added to . The output power is determined principally by the dc power input to the tube. When considering the efficiency of the amplitron, it is customary to refer to the dc-rf conversion efficiency of the tube. This efficiency relates the power added to the dc input power and is slightly different than the standard definition of efficiency, which relates total power output to total input power.
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