Чтение общенаучной литературы. Кытманова О.А. - 12 стр.

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УлГТУ | Ульяновск

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13
In broadcast work two or more transmitters are commonly assigned the same
carrier frequency, and in order to minimize the resulting interference it is essential
that the carrier frequencies be as nearly as possible the same.
The Microphone Transmitter. The microphone transmitter may be one of the
ordinary carbon granule type. Without going into details, it will suffice to state
here that such a microphone consists simply of an elastic diaphragm bearing
against a mass of carbon granules enclosed in a suitable chamber, the carbon
granules forming part of an electrical circuit, When the microphone is not being
spoken into the diaphragm remains stationary and exerts a constant pressure upon
the carbon granules, the resistance of which remains, therefore, constant. On the
other hand, when the diaphragm is set vibrating, as it is done by speaking into the
microphone or through a noise or sound reaching it, the pressure exerted by the
diaphragm against the carbon granules changes, and this change of pressure causes
the resistance of the carbon granules to increase or decrease in accordance with the
displacement of the diaphragm from its position of rest.
When the microphone is not being spoken into, the alternator produces a high-
frequency current of constant amplitude, i. e., an undamped current; the amplitude
of this current is adjusted to the maximum by adjusting the inductance so as to
make the natural frequency of the circuit equal to the frequency of the alternator.
Now, assume, for the sake of simplicity, a vibrating tuning fork to be placed in
front of the microphone. The harmonic vibrations of the tuning fork will bring
about harmonic vibrations of the microphone diaphragm, and these will produce
variations in the resistance of the microphone. Since no other part of the circuit is
undergoing any change, it is plain that a variation of the microphone resistance will
produce a corresponding variation in the amplitude of the high-frequency antenna
current. Thus, when the diaphragm is displaced inwardly the resistance of the
microphone and, therefore, of the entire alternator circuit, decreases, and the
amplitude of the current supplied by the alternator must necessarily increase, the
reverse taking place when the diaphragm is displaced outwardly.
Radio Transmitters
To use an oscillating tube
circuit, as part of a radio
transmitter the high frequency
oscillations in the L2C2 circuit
must be modified by sound waves
and then applied to an antenna
and ground system for
broadcasting as electromagnetic
waves.
A simplified circuit diagram showing one of the many ways of doing this is given
in the figure below. There are three parts to this particular "hook up", (1) the
microphone circuit containing a battery D and a transformer T, (2) the oscillator
circuit in the middle, and (3) the antenna circuit C1L1G at the left.

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