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Page:Popular Science Monthly Volume 90.djvu/494

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478

��Popular Science Monthly

��depend upon the electrical contact in the bearing of Fig. 9 alone; a small piece of thin spring wire (brass or phosphor bronze) should have one end soldered to the shaft just above the upper plate of the base bearing, its other end being fastened to the bearing itself after one or two spiral turns are made loosely about the shaft. This will prevent any possible trouble from oxidation of the contacts within the condenser. A stop should be provided to keep the plates from turning more than 180 deg. and twisting off the spring wire.

Assembling and Adjusting Manifestly the foregoing descriptions, with reference to Fig. 6, 7, 8 and 9, apply to the completed apparatus. The best way to assemble the instrument is to clamp to- getft^r the fixed plates on their four rods, independent of either the base or top plates of insulating material. When the conduct- ing plates are all set parallel and with the proper 3^-in. spacing, they are laid aside and the moving plates similarly assembled upon the shaft. The base, hand wheel and top are left apart until the moving plates have been correctly spaced and adjusted. Then the moving plates are slipped interleaf- wise between the fixed plates, and the insu- lating top put in place. By trial the proper number of washers and the best position of the clamping nuts is determined, and the top is then fastened. Next the base is ad- justed to the proper position, and all the fastening nuts tightened. Last of all the hand-wheel and pointer are added, and the scale set to the correct position. It is a good plan to cut a strip of celluloid film to just the width of the space between the insulating top and base, and to bend it around the metal parts so as to exclude dust. When this is to be done, the top and base may be made 5}4 in. square to give a little additional edge-space in which the celluloid strip may be fastened by gluing bits of 3^-in. felt next to it.

The next article of this series will de- scribe fully the use of the variable con- denser in the sharp-tuned secondary, as well as methods of adjusting the primary circuit by using the same instrument.

��An Easily Erected Antenna for Wireless Operators

ABOARD ships it is necessary to replace . aerial wires at least once a year on account of the action of the salt spray and the smoke and gases from the stack. In

��constructing an aerial it is usual to secure spreaders the proper distance apart and stretch the wires between. This necessi- tates the removal of the spreaders and their holders from the ship to the wharf or clear space where the work can be done, and often requires the labor of from two to four men for at least one day, depending, of course, upon the size of the aerial. To hoist the new aerial into place requires another half day, with additional men to assist in clearing the wires from davits, funnels, etc.

The aerial aboard a government vessel had to be renewed recently under a guaran- ty that the vessel would not be laid up, that the radio apparatus would not be kept out of operating condition for more than one hour, and that the same spreaders and attachments would be used. The pro- cedure to meet these conditions was as

���Ordinary snaps used on aerial lines to place them in position quickly on a vessel

follows: The phosphor-bronze antenna wire was measured off into the required lengths and a snap hook was fastened to each end. Inasmuch as heat applied in soldering this kind of wire invariably weakens it and makes it liable to part under strain at the point where the heat was applied, soldering the joints was dis- pensed with and patented sleeves or con- nectors were used. This allowed also greater speed in the construction.

When all the wire work was complete the old aerial was lowered to the deck and the wires quickly cut away. The new aerial was snapped into place and hoisted aloft. The actual time required in making the change was less than one hour, and the services of three men were required to hoist it in place. The making up of the wires, hooks, etc., can be done by one man, and by using this method an aerial can be installed in one-fourth the time and with only one-third to one-half the labor required by the old method. — Frank M. Meals.

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