Popular Science Monthly 



463 



A Motor-Operated Aerial Switch 



IN the DeForest sending equipment of 

 a certain station, no anchor gaps are 

 used, since the switching system for the 

 aerial consists of a large D. P. D. T. 

 switch with one side for sending and the 

 other for receiving. The operators could 

 not place the switch near the operating 

 table, since then the aerial and ground 

 leads for the sending set would have to 

 run a long way to reach it. This, of 

 course, is objectionable because these 

 leads induce high potentials in the light 

 and power wires in the station ; high 

 voltages may be induced even in the re- 

 ceiving set, burning out the detector and 

 so on. The switch was placed so that 

 the sending-set leads were of minimum 

 lengths, even though it had to be fas- 

 tened high up on the ceiling. At first, a 

 system of ropes over pulleys to work the 

 switch was used, but it was not easily 

 operated from the table and the entire 

 arrangement did not look 

 good. 



After having tried 

 several ideas, one was 

 found which is a work- 

 ing success, and the 

 switch is now worked 

 by a small, reversible se- 

 ries motor. A minia- 

 ture electric hoist, with 

 the motor, pulls a cord 

 so as to throw the 

 switch from one set of 

 jaws to the other. The 

 accompanying cut shows 

 the systems installed. 

 The winding apparatus 

 consists of a drum driv- 

 en from the motor shaft 

 by a reduction gear. 

 The drum is a wire spool having a 1 ^ •,•" 

 core and 3 Mi'' heads and made IV-/' 

 long by sawing some of the core off. 

 The cog wheels for the reduction gear 

 were taken from a telephone magneto. 

 The little cog was soldered on the motor 

 shaft and the big one screwed on one 

 end of the winding drum. The bearings 

 and shafts of the magneto drive were 

 also utilized. The shaft of the winding 

 drum is supported on the motor frame 

 by a bent piece of scrap iron and fastens 

 on the motor base. 



A series-wound motor, which drove a 

 ten-inch fan, is used. It draws about 

 one ampere from the 110-volt A. C. cir- 

 cuit. It is reversed with a small D. P. 

 D. T. battery switch. 



The cord is kept from slipping by ty- 

 ing a knot around a screw. The cord 

 is then wound a couple of turns in each 

 direction. One end goes to the switch 

 handle, where it is tied fast, and then 



By means of this system all the large switches may be controlled 

 directly from the radio table 



continues over a small awning pulley and 

 back to the other end, where the two 

 ends are tied together. 



Besides the duty of reversing the mo- 

 tor, the control switch must disconnect 

 the motor from service as soon as the 

 aerial switch has been thrown. This was 

 easily arranged by placing a bent spring 

 of No. 16 or No. 18 brass between each 

 pair of jaws of the control switch. Thus 

 the switch handle kicks open and leaves 

 the motor out of circuit, as soon as you 

 release pressure, on either side. 



