Manual of wireless telegraphy and telephony by Collins A. Frederick (Archie Frederick) 1869-

Author:Collins, A. Frederick (Archie Frederick), 1869-
Language: eng
Format: epub
Tags: Telegraph, Wireless, Radio
Publisher: New York, J. Wiley
Published: 1913-03-25T05:00:00+00:00

T Grpund Fig. 96.—Hot-wire Ammeter in Aerial.

moved together until a point is found where the reading of the anuneter is the highest; to ascertain this the primary circuit must be closed by the key for a sufficient length of time to permit the needle of the ammeter to come to rest

Having gotten the best results in this manner, a longer shunt may now be inserted in the ammeter and the upper contact-plug or clip moved gradually away from the lower contact, when a position will soon be reached where the reading of the ammeter will give a still higher value, showing that now the open-circuit aerial-wire system and the closed oscillation-circuit are more or less accurately tuned to the same periods. If the interrupjor is of the mercury-turbine or electrolytic type, it may be further adjusted and a greater amount of energy can be used; then the upper plug or clip may again be adjusted until the reading is maximum, when the circuits may be said to be fairly well tuned. As the hot-wire ammeter is not a very accurate instrument, several readings should be taken to determine the value of the current energy of the oscillations surging in the aerial wire, and the mean reading taken as standard.

To Tune the Aerial-wire System to Emit a Given Wavelength. —The best results are obtained in wireless telegraphy when the transmitter and receptor are tuned to the same wave-length; when they are thus tuned so that they will be CO-resonant they are said to be syntonized. Where only two stations are engaged in communication the receiver can be tuned to the same period of oscillation as the sender, as will be described presently; but when a receptor is to receive messages from two or more transmitters, it then becomes necessary to tune each of the latter to emit waves of a length suitable for the receptor.

It has been previously stated that a plain aerial wire

system, that is, one in which there is neither inductance coil nor condenser inserted, will emit a wave approximately four times its length, and therefore where two or more sending stations are to be used in connection with one or more receiving stations the aerial wires of the former should be practically the same length. While it is comparatively easy at shore stations to have the aerial wire of the same length, on board ship the conditions met with are very different; yet, as, for instance, in the Navy and the mercantile marine service, it is essential that all stations, both on ship and shore, should use the same wave-length.

(a) This is accomplished in the following manner: First, a wave-length should be selected that is equal to or a little longer than that emitted by the longest of the aerial wires used. A tuning-device, of which one form is shown diagramatically in Fig 97, is called into action. This device comprises an adjustable spark-gap formed of needle-points, a condenser of small capacity, and a portable tuning-coil of the

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