710 



BELL SYSTEM TECHNICAL JOURNAL 



are illustrated in Fig. 6. The basic advantage of the GL-2C40 tube for use 

 at high frequencies is found in its construction, whereby the tube elements 

 are arranged to form an integral portion of the external circuit with a mini- 

 mum of mechanical disturbance. At these frequencies external coupling 

 circuits of the transmission line type are usually employed. This tube 

 when operated at an anode potential of 250 volts has a mutual conductance 

 of approximately 6000 micromhos and an amplification factor of vS5. It has 

 been customary to employ one or two stages of RF ampliiication associated 



50 



FREQUENCY IN MEGACYCLES PER SECOND 

 100 200 300 500 1000 2000 3000 5000 



500 300 200 150 100 80 60 40 30 20 15 

 WAVELENGTH IN CENTIMETERS 



Fig. 5. — Comparison of noise figures for point-contact silicon crystal rectifier and 

 GL2C40 vacuum tube. 



with the nonlinear element and a beating oscillator using this same tube. 

 The reduced performance of the GL-2C40 tube as a converter element as 

 indicated in Fig. 5 is not of imj)ortance, if sufficient gain is provided prior to 

 the actual conversion process, and the ability of this vacuum tube to operate 

 at higher levels is a positive advantage. 



The electrical circuit design techniques employed in this frequency region 

 are based on the use of transmission line elements in place of the more or 

 less orthodox luni])ed clement configurations at the lower frequencies. The 

 difficulties experienced in i)racti(al designs of radar converters of this type 

 revolve about successfully terminating and satisfactorily isolating each stage 

 so that confusing and inefficient interaction effects are minimized. 



