152 



Popular Science Monthly 



An Easily Made Switch for Grounding 

 Aerial Wires 



UNDERWRITERS require that wire- 

 less antennas shall be well grounded 

 when not in use. To do this, it is necessary 

 to use a switch capable of withstanding 



A switch of large proportions for 

 grounding high voltage aerial wires 



high voltage. These switches are rather 

 expensive. One can be made cheaply with 

 very little trouble. The material required 

 for its construction is as follows: 



1 8 in. of I -in. by 3^-in. copper bus bar. 

 3 in. of ^-in. sq. copper bar 

 Six I -in. 8-32 brass machine screws 

 Three I M-in. 8-32 brass machine screws 

 1 hardwood handle 



I piece marble or slate, for base, 4 ins. by 

 15 in. by i in. 



With a sharp hack-saw cut the ^-in. 

 square bar in the center lengthwise and 

 then crosswise, making 4 pieces i3^ in. by 

 ^ in. by ^ in. Only three are used and 

 these are cut as shown in the detail drawing. 

 The i-in. by J^'s-in. copper bus bar is then 

 cut into a 9-in. strip for the lever and six 

 i3^-in. lengths for the jaws. These fit 

 into the slots cut for them in the ^-in. 

 stock. They are held in place by drilling 

 two 3^8-iri. holes through the entire unit 

 and putting in rivets. A ij^-in. machine- 

 screw passing through the 5/32-in. hole, 



' — 1' — ^ i'-* 



Dimensions for making the parts for 

 the high voltage single throw switch 



holds the jaws firmly in place on the base 

 of the switch. 



To hold the center jaws to which the 

 lever is pivoted, it is necessary to have an 

 extra machine-screw passing up through the 



switch-base and into a hole drilled and 

 tapped into the copper. This prevents aU 

 possibility of the lever swinging to either 

 side. A 3^-in. slot is cut in the handle 

 about I in. deep. Two machine-screws 

 hold it in place. 



The switch should be fastened to the 

 house just outside a window in the wireless 

 room, where it can be reached easily. The 

 antenna is connected to the lever at the 

 center of the switch by soldering the wire 

 into a lug made by flattening and drilling 

 a short piece of copper tubing. In like 

 manner the lead-in is connected to the 

 upper set of jaws and the ground wire to 

 the lower set. 



The "ground" should consist of about 

 10 sq. ft. of a good conductor buried in 

 moist earth and connected to the aerial 

 through the switch by a length of No. 4 

 copper wire. — Harvey N. Bliss. 



PART CUT 



A Floor-Push for Operating 

 the Test-Buzzer 



A FLOOR-PUSH is a great improvement 

 over a key or switch to control the 

 buzzer-test, for it is out of the way and 

 leaves both hands 

 free to manipulate 

 the instruments. 



An inexpensive 

 and satisfactory one 

 can be made from a 

 common wood push- 

 button. The flange 

 around the center is 

 cut off so that the 



Floor push made 

 from push-button 



button projects some distance above the 

 wood. The push is then connected in the 

 usual manner and operated by motions 

 of the foot. — Bruce M. Mills. 



The Efficiency of a Wireless 

 Receiving Station 



WHEN passing electromagnetic waves 

 set up currents in a tuned receiving 

 antenna, the energy in that aerial system 

 is drawn from the waves themselves. By 

 no means all of the power thus taken from 

 the waves is useful, however, for some of 

 it is wasted in heating the wires, instru- 

 ments and ground connection. A large 

 part is re-radiated into space; for the an- 

 tenna carrying radio frequency current 

 acts just like a feeble transmitter even 

 while it is receiving. Only one-half of 

 the absorbed power is used in the receiver. 



