Recent Radio Inventions 



Microphonic Relays; An Unusual Quenched Spark-Gap; 

 a Shpping-Contact Detector 



By A. F. Jackson 



FOR a number of years inventors 

 struggled to produce microphonic 

 relays, but their work was practi- 

 cally without substantial success. It was 

 not found possible to build an instrument 

 which would magnetically modulate the 

 current through a microphone contact in 

 such a way that all the vibrations of the 

 human voice could be reproduced and 

 magnified. This, 

 nevertheless, d i d 

 not prevent the de- 

 velopment of mi- 

 crophonic relays 

 that would aug- 

 ment the energy of 

 current having a 

 single definite fre- 

 q u e n c y. Instru- 

 ments of this sort 

 are shown in 1915 

 U. S. patent No. 

 1,163,180, issued to 

 W . Schloemilch 

 and A. Leib. 



One arrangement 

 of this patent is 

 shown in Fig. 1. 

 The antenna, tun- 



Fig. 1 . With a microphonic relay of this sort, 

 tremendous magnifications may be obtained 



ing and rectifying system a, h, c, f, leads 

 the converted, pulsating energy of the 

 received waves to the first amplifier di. 

 This consists of a wire vibrating system 

 gi connected mechanically to a micro- 

 phone hi. The tension of the vibrating 

 Avire is variable, and is to be adjusted so 

 that its mechanical period is the same as 

 the sound period of the incoming wave 

 groups. Thus the wire is made to vi- 

 brate, through resonance, and a great 

 effect is produced upon the microphone. 

 The current from battery ki \s varied by 

 the first relay and led through the mag- 

 nets and the second-step relay, which 

 controls the current from a second bat- 

 tery. The second step of amplification 

 is carried into the third relay and its 

 output through switch m either into the 

 loud-speaking telephone n or into the 

 delicate contact relay p, the final relay 



01, and the Morse printer o. The relay 

 p is not of the microphonic type, like 

 those of the first three steps, but has a 

 tuned wire pi in contact with a sluggish 

 spring p2. 



When signals are received of the 

 group frequency to which all these re- 

 lays are attuned, the third-step relay 

 sends a strong current into the intensi- 

 fying instrument p. The vibrations of the 

 wire pi practically open the local circuit 

 of this last named 

 apparatus and so 

 permit the final re- 

 lay to close and 

 the Morse printer 

 to register. This 

 same microphonic 

 amplifying appara- 

 tus may be applied 

 to sustained-wave 

 reception, if an in- 

 terrupter is insert- 

 ed at either the 

 sender or receiver; 

 in this case, the vi- 

 brating wires are 

 tuned to the inter- 

 rupter frequency. 

 In the same way, beats or heterodyne 

 receivers may be used, and the relays 

 tuned to the resulting signal frequency. 

 With apparatus of this kind, tremendous 

 magnifications of signals may be ob- 

 tained; the microphonic relays must, 

 however, be protected from vibration 

 and kept in accurate adjustment. In 

 place of the intensifying relay p, a trans- 

 former and rectifier may be used to make 

 the amplified alternating currents oper- 

 ate a direct-current relay. 



By the combination' of large amplifi- 

 cation from the microphone relays, con- 

 nected in cascade, with exceedingly sharp 

 resonance to tone frequency, some ex- 

 tremely interesting results have been se- 

 cured. Using a single receiving antenna, 

 tuner and detector, it has been found pos- 

 sible to record, on separate Morse tapes, 

 messages from three different transmit- 



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