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Updated: May 21, 2025
The required parts are the 50 watt tube; the grid leak resistance; the filament rheostat; the filament storage battery; and the magnetic modulator. It is not advisable to use an induction coil for the modulator for this set, but use, instead, either a telephone transformer, or better, a magnetic modulator of the second size which has an output of from 1-1/2 to 3-1/2 amperes.
In the better makes of microphone transformer, there is a third winding, called a side tone coil, to which a headphone can be connected so that the operator who is speaking into the microphone can listen-in and so learn if his transmitter is working up to standard. The Magnetic Modulator.
The Reverend Harper Freeman's voice could hardly, even by courtesy, be called musical; in fact, it was harsh and strident; but this evening the hills, and the trees, and the wide open spaces, Nature's mighty modulator, subdued the harshness, so that the voice rolled up to the people clear, full, and sonorous. Nor was the preacher possessed of great learning nor endued with the gift of eloquence.
Since the microphone current is absolutely distinct from the oscillating currents surging through the coil of the transformer a very small direct current flowing through a coil on the latter will vary or modulate very large oscillating currents surging through the former. Operation of the Vacuum Tube as a Modulator.
The voltage of the grid of the modulator tube is varied by the secondary coil of the induction coil or microphone transformer, above described. In this way the modulator tube acts like a variable resistance but it amplifies the variations impressed on the oscillations set up by the oscillator tube.
As the magnetic modulator does the same thing a vacuum tube used as a modulator is not needed where the former is employed. For this reason a magnetic modulator is the cheapest in the long run. The Operation of Wireless Telephone Transmitters with Alternating Current.
He had to be listening beforehand, and with his instrument aimed right, too. So Lockley flipped the modulator switch and turned on the instrument. He said patiently, "Calling Sattell. Calling Sattell. Lockley calling Sattell." He repeated it some dozens of times. He was about to give it up and call Vale instead when Sattell answered. He'd slept a little later than Lockley.
In addition to singing from the hand signs, and from the Sol-fa 'modulator' which is gradually being constructed on the board, the children can now sing from the horizontal Sol-fa notation, and from the staff notation. The first of these is invaluable in the early stages, as it absolutely precludes guessing.
In the first way the secondary terminals of the modulator are shunted around the grid leak in the grid circuit as at A, and in the second the secondary terminals are connected in the aerial as at B. Where an induction coil or a microphone transformer is used they are shunted around a condenser, but this is not necessary with the magnetic modulator.
The voltage of the grid of the modulator tube is varied by the secondary coil of the induction coil or microphone transformer, above described. In this way the modulator tube acts like a variable resistance but it amplifies the variations impressed on the oscillations set up by the oscillator tube.
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