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BELL SYSTEM TECHNICAL JOURNAL 



from all causes of from 0.1% to .01%. The possible influencing fac- 

 tors include temperature, atmospheric i)ressure, supply voltage, and 

 load impedance variations with time, and mechanical shock and 

 vibration. 

 C. It is extremely desirable that frequency control of the beat oscillator 

 be available by remote electrical means. The use of automatic tuning 

 control of a military radar receiver has proved a necessity during the 

 past war and, as will be discussed in a later section, the rates of change 

 of frequency encountered are found to be quite great. This requires 

 essentially that an electrical control method of continuously adjusting 

 the beat oscillator frequency be employed to obtain satisfactory re- 

 ceiver performance. 



OUTPUT 



Fig. 16. — 1000-nic Radar local beat oscillator employing GI^-2C40 vacuum tul)c — 

 chematic diagram. 



D. It is desirable that the output of the beating oscillator tube be free 

 from noise. In the usual radar system, if the output frequency of the 

 beat oscillator is modulated with noise, a reduction in receiver per- 

 formance will result. As previously discussed, the development of 

 the balanced converter has provided the converter designer with some 

 relief from this noise source and in this case this requirement assumes 

 less importance. 

 A beat oscillator arrangement utilizing the GL-2C40 lighthouse tube, as 

 develoj)ed for a military radar system operating in the 1000 mc region, is 

 indicated in Figure 16. This assembly is quite similar mechanically to the 

 RF and converter components employed in this frequency region and 

 described previously. The positive feedback necessary to sustain oscilla- 

 tion is provided by means of a feedback coupling probe as shown. The 

 oscillator out])ut is available by means of a pick-up loop inserted into the 



