Page:Popular Science Monthly Volume 90.djvu/168

 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,

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��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.

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