Page:Popular Science Monthly Volume 91.djvu/175

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The contacts should be gone over frequently with very fine sandpaper, as a poor contact is liable to cut down the efficiency of the receiver to no small extent. The left contact-screws are adjusted to touch the springs when the key is depressed while the right hand pair are to make

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��Popular Science Monthly 159

Loading Coil in Series with the Secondary

WHEN a low resistance detector is used, it is a good plan to tune the secondary circuit by using a comparative- ly small inductance coil and a large con-

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Detail of the parts that enter into the construction of the magnetic break key

contact when the armature has come back, and to break the contact when it has been drawn to the magnets.

A little experience will make it possible to get an adjustment where there is no sparking at the contacts and no noise in the telephones.

I doubt if anyone, after using a key such as described, will ever willingly go back to the old clumsy aerial switch.

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denser, for then the current flow is a maxi- mum and the voltage is quite low. For high resistance detectors the reverse is true. Increased efficiency with such de- tectors as the audion can frequently be secured by inserting a loading coil in series with the secondary, and correspondingly reducing the capacity of the tuning con- denser. This applies the highest possible voltage to the grid.

��An Emergency Form for Winding Motor Fields

RECENTLY my rotary spark-gap, no- . volt A. C. motor burned out one of its fields. As I was in a hurry to use it I tried a quick method of rewinding the coil by driving a series of nails into a wood face-plate on a small lathe and winding the wire on them. After winding the coil I bent the nails together so that the coil could be slipped off. — Edward McClure.

��Effect of the Moon and Season on Wireless in the Tropics

WHILE stationed in the tropics for several years as a wireless operator, I observed that in the periods of a full moon, or thereabouts, the atmospheric interferences are slight and the ether seems to carry the wireless waves with less ab- sorption than when the moon is in its quarter periods, or thereabouts. With a full moon, and using the same receiving set, I could receive from stations that were about 200 miles farther away than those which could be heard when the moon was in its first or last quarter. Also, during the winter months from about the first of December to April, there seemed to be bet- ter atmospheric conditions.-#-J. M. Cohen.

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