Morse4 - execubic
Morse4
~ Hoping that the previous lessons have went well, we increase to 6 wpm to continue with the same speed in lesson 5. =
In the beginning, receivers had to rely completely on the power coming from the antennas, because there was nothing that could amplify the signals. Thus, the energy of the dots Marconi heard in 1901 came from the transmitter in England. But that was changed in 1906. =
That year the American engineer Lee de Forest made an important invention. Two decades before, Edison had found that an electric current could pass through a bulb if a plate with positive voltage had been placed near the glowing filament. That was a great mystery till the electron was discovered in 1896. Then it was clear that electrons were emitted from the hot filament and then drawn to the positive plate, the anode. =
de Forest got the idea of putting a metal grid between the anode and the filament. By altering its voltage, he was able to control the current. When the grid was made more negative in respect to the filament, electrons were repelled, and so the current decreased. A positive voltage instead helped accelerating electrons towards the anode, increasing the current. =
In this way it became possible to amplify signals. The tiny energy delivered by eg a microphone could be amplified to give a strong sound from a loudspeaker. de Forest naturally took a patent and then tried to rise funds for further development by advertising about stocks being sold. For that he soon was prosecuted, trying to swindle people on apparently false promises. But the inventor was able to show that the gadget really worked, so it all ended well. =
The arrangement is a kind of electronic valve. With the filament, called cathode, the grid and anode, it has three electrodes, giving it the name triode. These valves, named tubes in the US and in Sweden lamps in the beginning, meant a revolution. The first computers could employ tens of thousands of triodes. Not until 1948, when the transistor was invented, the next great step forward was taken. +
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