men FREQuniwcy .-iMPurinRs 



197 



From lliis t.il)lc it is sei'ii thai tlu' i-lTi'il of tin- in|)iit iiiipi'cl.iiKe is 

 nckjli^ilile at frfqui-iu-ics up to alK)iit KM). (100 cvik-s, l)iit for fri.'(|iU'iic-ies 

 in iho broadcast iiij; range, tlie injnit iiniH'<i.iiu-e will introdure an 

 apprcriabic loss in the ])ri'caling circuit, which will result in a drop 

 in aniphtication la-low the value obtained for a single stage amplifier. 

 It is stH-n that the input impedance R'j. for broadcistiiig fre(|uencies 



Fig. 11 — .Amplification Curve of Two Stage Loosely Coupled 

 Transformer Amplifier 



is of the same order of magnitude as the plate impedance Rp. which 

 means that it will be of no advantage to use much step-up in choke 

 coils or timed circuits for an amplifier with more than one stage, since 

 the amplification in no case will be much higher than m per stage, 

 except for the last stage, which is working into the detector. 



The loosely coupled transformers of the type already discussed 

 will, on the other hand, work very well in a two-stage amplifier, since 

 there is no step-up used in these, and the amplification will be very 

 nearly twice the amplification for a one-stage amplifier, as will be 

 seen from the amplification curve shown in Fig. 11. The width 

 of such an amplification curve can be increased by proper adjustment 

 of the transformer inductances but the amplification will naturally 

 drop correspondingly. 



