Page:Popular Science Monthly Volume 89.djvu/288

 274

��Popular ScieJice Monthly

��tioiis, and in it is shown a complete transmitter. Power is conveyed from the generator ii, of approximately 500 cycles, to the transformer primary 19 by way of the signaling mechanisms controlled by sending keys 17 and 23. In the first of these a direct current from battery 16 energizes the magnets of relay 12, 13, 14, whose contacts short circuit a portion of the impedance 18, 18' (which is shown as a trans- former with the secondary arranged to be shunted by the relay) and thus allow the main current to pass. Wind- ings on the relay contact-arm prevent it from opening until the alternating cur- rent passes through zero amplitude, and thus sparking is avoided. The alter- native method of signaling is by key 23, which in its lower position neutralizes the impedance of coils 21 and 22 by closing a differen- tially-wound sec- ondary circuit 21^ 22' and so provides an unobstructed path for the main primary current.

The 500-cycle potential from the secondary of the power transformer 19' charges the main condensers 20 through the choke-coils 47, 48. F"rom the con- densers the circuit {)asses through sta- tionary electrode 38, across one spark- gap to the rotor 41 and then back to a second stationary electrode 39. From here the primary oscillations are led through the transformer coil 28 and back to the condenser. The secondary 28' is connected to antenna 26 and ground 29 in the usual way, and the ammeter 27 is inductively coupled to the antenna circuit. A protectixx- spark- gap 35 is connected across the main rotary gap, so as to prevent damage from excessive potentials. With con- nections as outlined, if the rotary gap is I)rovided (as shown) with one si)oke for each pair of field poles in the alternator upon whose shaft il is mounted, there will occur oidy one spark for each complete cycle of alttrnating current.

���A radio transmitter suitable for sending

messages on half power by using the lower

spark frequency

��If, howe\er, a second pair of stationary electrodes 37 and 40, spaced exactly half-way between the first pair (as regards the electrical cycle), are con- nected into circuit, there will be a spark for every half-cycle. That is to say, by connecting the additional electrodes into the primary oscillation circuit there are given twice as many opportunites for sparks to pass. The change in connec- tion may be made by moving key 25, which controls the output of battery 24 and thus operates relays 36 and 30. When the key is up the transmitter produces 500 sparks per second, and when it is down, 1,000 per second. Thus the signal tone is changed by a full octave, and by mechanically or electrically linking together 25 and i of the signaling keys 17 or 23, dots or dashes may be sent at either pitch of spark-note.

The patent also contains nine other drawings showing details of the spark- gap and stationary electrodes with water cooling (such as is indicated by the pump 45 and circulation system 44), types of oscillation transformers for heavy current, \ariable loading induct- ances, high and low potential relays, etc. -A transmitter in which the alter- nator produces a high \"oltage which may be connected directly across the spark- gap is also illustrated and described.

A Booth for Long Distance Receiving

TROUBLE is sometimes experi- enced in recei\ing the faint wireless signals during rainy weather, on account of the noi.se caused 1)>- the rain pounding on the roof of the wireless room.

This trouble can be o\ercome by building a small double-walled booth, similar to a telephone booth, witiiin the ro(jm in whivh the outfit is placed. Saw- dust should be i)ackeil between the walls and \entilation provitleil \i\ means of two tubi'S, one in the lop and the other near the bottom.

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