Page:Popular Science Monthly Volume 88.djvu/491

 Popular Science Monthly

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��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.

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