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The groanings are here not there. You haven't been able to get in over there to attach anything, have you? What do you mean?" "No," he admitted, "but did you ever hear what you could do with a microphone, a rheostat, and a small transformer coil if you attached them properly to a direct-current electric lighting circuit? No? Well, an amateur with a little knowledge of electricity could do it.
He adopted the same method of modulation using a record player amplifier and an Astatic crystal microphone. W.A.C. was achieved by February 1948 with about 50 watts of R.F. into a simple dipole antenna. During the ten months that SV1WE was active 750 QSL cards were sent out. Of the 61 countries worked only 49 were confirmed.
"Have you an eavesdropping microphone, Haljan?" I hesitated. "Yes." "I was thinking...." He leaned closer. "If, in half an hour, you could use it upon Miko's cabin I would rather tell you than anyone else. The cabin will be insulated, but I shall find a way of cutting off that insulation so that you can hear." So George Prince had turned with us.
Holding the microphone close to the young engineer's mouth, Connel said, "Tell us everything you know of this incident." Barret spoke slowly and carefully, describing how he and Professor Hemmingwell had been at the other end of the hangar when the explosion had occurred.
The arrangement will be understood from figure 92, where P and P1 are two similar coils or bobbins of thick wire in circuit with a battery B and a microphone M, while S and S1 are two similar coils or bobbins of fine wire in circuit with a telephone T. It need hardly be said that when the microphone M is disturbed by a sound, the current in the primary coils P P1 will induce a corresponding current in the secondary coils S S1; but the coils S S1 are so wound that the induction of P on S neutralises the induction of P1 on S1; and no current passes in the secondary circuit, hence no sound is heard in the telephone.
Lawrence lifted up the plain black box and with it he pulled up the wires which I had so carefully concealed in the cracks of the floor. "That," said Kennedy, "is a little instrument called the microphone. Its chief merit lies in the fact that it will magnify a sound sixteen hundred times, and carry it to any given point where you wish to place the receiver.
But the delicate microphone would not carry these stronger currents. Increased sensitiveness in the receiving apparatus was also necessary. Not content with their accomplishments in increasing the scope of the wire telephone, the engineers of the Bell organization, headed by John J. Carty, turned their attention to the wireless transmission of speech.
The only difference in the operation of these sets is the substitution of the microphone transmitter for the telegraph key. The Microphone Transmitter. By referring to the diagram at A in this figure you will readily understand how it operates.
In the wireless telephone transmitters for long distance work which were shown and described in the preceding chapter a battery is used to energize the microphone transmitter, and these two elements are connected in series with a microphone modulator.
Climbing into the craft, he picked up the audioscriber microphone and recorded a brief message. Removing the threadlike tape from the machine, he returned to the house and left it on the spool of the audioscribe-replay machine near the front door.
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