11-7] 



THE PLATINOTRON 



605 



Nearly all of the signal generated within the amplitron comes out of the 

 output end, and very little out of the input end. When the direction of 

 magnetic field is reversed, the functions of input and output terminals are 

 exchanged, but there is no other effect on the performance. It has been 

 determined that the rotating electron cloud interacts with a backward 

 wave on the slow wave structure. However, the device differs from the 

 M-Carcinotron in the cathode structure employed. The electron beam 

 in the stabilotron is re-entrant; in the M-Carcinotron it is not. 



The conditions under which the platinotron is operated determine the 

 gain that can be obtained. With low modulator input and magnetic field, 

 relatively large gain can be obtained, in the order of 20 db. The available 

 gain is reduced as the modulator input and magnetic field are increased. 

 Under the most efficient conditions of operation, a relatively large signal is 

 required to lock the output frequency to the input and the available gain 

 is only a few decibels. This characteristic is illustrated in Fig. 11-32. 



100 P, 



0.01 R 



100 P„ 



RF POWER INPUT 



Fig. 11-32 Gain Characteristics of AmpHtron. 



Amplitrons can be operated in cascade to increase the gain, but this 

 operation is made difficult by the fact that a signal reflected from the 

 high-level output is reflected back through the chain of amplitrons and will 

 appear as a relatively large reflected signal to the input of the chain. This 

 situation can be improved by placing attenuators or isolators between 

 adjacent amplitron stages. 



The potential usefulness of the low-gain, high-efficiency mode of oper- 

 ation can be appreciated when it is remembered that the drive signal is 

 transmitted through the amplitron with little attenuation and adds to the 

 amplitron output. In this way the amplitron can be used to boost the 

 power of a conventional radar. A signal reflected from the target will be 

 transmitted back through the amplitron in the reverse direction, so that 

 duplexing can be accomplished at the amplitron input. This can be 

 important when the duplexer limits the power level of the radar. 



