///(,// l-RF.Ql'Ei\'Cy AMl'l.lllf.RS 



185 



iiil'orin.iiioii th.il llu- in,i\inuini .iinpliru.uioii (il>t,iiiKil>U' willi .1 

 tiiniHl liriiiit aniplilicr is proimrtion.il to llio ratio oj the inductive 

 reactance to the Siiiiare root of the resistance. In the case of an ordinary 

 selective rircnit siuh as a tuned loop antenna the output voltage 

 develojxtl is pro|)ortional to the ratio of the inthictive reactance to 

 the first pcnver of the resistance. This does not mean that low resist- 

 ance is less desirable in ainplilier coils than in ordinary tuned circuits 

 but it does mean that tiie penally exacted 1)\' increasim; ilu' resist- 

 ance is not as great. 



In order to test the formulas given 1)\- eciuations (.")) and (0) a 

 series of experiments have been carried out. 



For measurements of the maximum amplification of a tuned circuit 

 ami)litier a circuit as shown in Fig. 3 was used.' The grid of the am- 



jj_H'IH-l' T ' • '['['hj^ 



Fig. 3 — Method of Measurement of Tuned .Amplifier 



plitier tulie I is connected up to a known resistance, through which is 

 passed a known current, and the voltage across the tuned circuit is 

 measured by ineans of the tube-voltmeter II. The inductance Li/.j 

 is made up of a single layer solenoid closely wound with 17;i turns of 

 solid wire and its value was 1.()3X10"' henries. 



Keeping the frequency and the input from the oscillator constant 

 the circuit is tuned to resonance by means of the variable condenser 

 C and the lead from the plate to the coil is then moved along the coil 

 until a point is reached which gives maximum deflection of the tube- 

 voltmeter. During this process it is necessary to retune the circuit 

 for each new fKiint tried. Having thus obtained the right step-up 

 for a certain frequency we then measure the amplification for different 

 frequencies and get the amplification curves shown in the upper half 

 of Fig. 4. On the lower half of Fig. 4 are given the number of turns 

 (Lj) across the plate of the amplifier tube and also the capacity of 

 the condenser C for each of the four cases shown. 



' For a more detaile<l description of the method of measurement, see section en- 

 titled "Measurements" lielow. 



