A Telephone Receiver of New Design 



By Charles Horton 



>TpHERE has lately appeared on the 

 X market a new type of wireless re- 

 ceiver that is claimed to be far more 

 sensitive than any in present use. The 

 extreme sensitiveness of this new re- 

 ceiver is due to the employment of an 

 entirely new and novel arrangement of 

 parts. 



In the accompanying drawings ap- 

 pears a semi-diagrammatic view of such 

 a receiver arranged to show clearly the 

 arrangement of parts, as well as three 

 views showing the operation of the re- 

 ceiver. 



The new receiver consists of a ring 

 type permanent magnet, A, provided with 

 U-shaped pole pieces of soft iron, B l 

 and B 2 . Supported between these two 

 pole pieces is arranged a flat coil of high 

 resistance, C, having a slot at its center 

 in which is balanced an armature, also of 

 soft iron, D, which is arranged for lim- 

 ited rotation about the pivot E in the 

 center of the coil. One end of this ar- 

 mature, D, is connected by means of the 

 wire, G, to the mica diaphragm, F. All 

 the parts described are neatly mounted 

 in a hard rubber case of the usual head 

 type. 



The operation of the receiver is appar- 

 ently as follows : 



In Fig. 2 the arrows on the perma- 

 nent magnet represent the path and di- 

 rection of the magnetic flux in the re- 

 ceiver when no current is flowing in the 

 coil, and it will be seen from this that 

 the flux produced by the magnet di- 

 vides equally through the two limbs of 

 the U-shaped pole pieces and to the 

 lower pole pieces, it is under no strain 

 whatever, and consequently the mica 

 diaphragm is not at all deflected. This 

 is quite a contrast to the state of the 

 diaphragm in the ordinary receiver, 

 which is deflected towards the permanent 

 pole pieces at all times. 



If, now, a current is caused to flow 

 through the instrument, say a direct 

 current of constant value, the coil sets 

 up a flux through the armature longi- 

 tudinally; this flux, as in all solenoids, 

 passing out of one end of the coil and 



in at the other, as shown by the arrows 

 in Fig. 3. The flux also divides and 

 flows equally in both U-shaped pole 

 pieces and thus the armature at both 

 ends is equally attracted to upper and 

 lower pole pieces and is thus under no 

 tendency to change its position. It will 

 be seen that acting separately neither the 

 flux due to the permanent magnet nor 

 the flux due to the coil has any effect 

 on the armature. 



The action is quite different when both 

 fluxes are acting simultaneously. In Fig. 

 4 this effect is clearly shown by the ar- 

 rows. The flux from the permanent 

 magnet in attempting to pass up through 

 both branches of the lower U-shaped 

 pole piece meets in the left branch a part 

 of the flux due to the coil, which is in 

 the same direction as itself. On the 

 other hand, the flux, in attempting to 

 pass up through the right branch, is op- 

 posed by the same flux from the coil, 

 which passes downward. Likewise, the 

 permanent magnet flux in continuing its 

 flow upward attempts to pass up through 

 the left branch of the upper U-shaped 

 pole piece and is here opposed by the 

 descending flux from the coil, while in 

 the right branch it is assisted by the 

 ascending flux from the coil. The final 

 result of this opposing and assisting of 

 the flux from the permanent magnet is 

 to cause a strong flux to flow in the 

 magnetic circuit as shown by the arrows 

 and a weaker flux to flow in the parts of 

 the magnetic circuit not included in the 

 circuit outlined by the arrows. Owing* 

 to the strong flux the armature is at- 

 tracted at its left hand end to the lower 

 pole piece and at its right hand end to 

 the upper pole piece and consequently is 

 slightly rotated on the pivot E. The 

 movement is transmitted to the mica dia- 

 phragm through the link G. 



It will now be easily understood that 

 should a current flow in the coil in the 

 opposite direction to that which we pre- 

 viously supposed, the resultant flux in 

 the magnetic circuit will be from the 

 lower end of the permanent magnet up- 

 ward through the right hand branch of 



390 



