VACUUM TUBES, THE HEART OF MODERN RADIO

JULY 24, 2018

I started this new topic beginning with the vacuum tube. Edison started it all. He just wanted a bulb and somewhere it is claimed that he himself stumbled upon the diode property in his tube but ignored it. a British bough his tubes and experimented and got the credit. John Fleming.

But it did not stop with Fleming. Others played around with Edison's bulb.  We can say that the real inventor of a vacuum device was Edison. Fleming made it into a DIODE. Back to America in 1906 , Lee De Forrest invented the TRIODE.

Vacuum triode

The basic vacuum tube (vacuum diode) is used to convert the alternating current into direct current. However, they cannot amplify the electric signal. In other words, they cannot amplify the voltage or power. To amplify the electrical signal, an extra electrode is required. When the extra electrode is placed between the cathode and anode, the resulting electronic device is called vacuum triode.

The name itself indicates that, it has three electrodes: cathode, anode, and control grid. American electrical engineer Lee De Forest invented the first electronic amplifying device (vacuum triode) in 1906 by adding an extra electrode (control grid) between the cathode and anode. Vacuum triode is a 3-electrode device that amplifies the electrical signal.

Electrodes of vacuum triode

Vacuum triode consists of three electrodes: anode, cathode and control grid. The anode, cathode and control grid are enclosed in an empty glass envelope. The cathode is surrounded by a control grid, which is in turn surrounded by anode. The construction of vacuum triode is similar to vacuum diode. However, vacuum triode contains an extra electrode (control grid). 

Cathode emits the free electrons when it is heated. Hence, cathode is also called as emitter. The process by which cathode emits the free electrons when it is heated is called thermionic emission. Anode collects the free electrons that are emitted by the cathode. Hence, anode or plate is also called as collector.

In between the anode and cathode, control grid is present. Control grid is placed more nearer to the cathode than anode to increase the electric current efficiently. Control grid will control the flow of electrons between the cathode and anode. Hence, control grid is also called as electron controller or electric current controller.

Control grid is made of network of wires that controls the electrons flow between the cathode and anode. The space between the network of wires in the grid is very large. Hence, the free electrons move easily from cathode to anode through the opening of the control grid. Free electrons that are moving from cathode to anode will carry the electric current.

In 1906, the US (Admiral Dewey) just dislodged the Spaniards from Asia.  Dewey with modern steam vessels sank Admiral Montojo's navy of sail ships to the bottom of Manila Bay. The world was young and yet technology began to appear.

The TRIODE made all the difference cuz it could amplify weak signals.

 The vacuum-tube feedback oscillator was invented around 1912, when it was discovered that feedback ("regeneration") in the recently invented audion vacuum tube could produce oscillations. At least six researchers independently made this discovery, although not all of them can be said to have a role in the invention of the oscillator.^[22][23] In the summer of 1912, Edwin Armstrong observed oscillations in audion radio receiver circuits^[24] and went on to use positive feedback in his invention of the regenerative receiver.^[25][26] Austrian Alexander Meissner independently discovered positive feedback and invented oscillators in March 1913.^[24][27] Irving Langmuir at General Electric observed feedback in 1913.^[27] Fritz Lowenstein may have preceded the others with a crude oscillator in late 1911.^[28] In Britain, H. J. Round patented amplifying and oscillating circuits in 1913.^[24] In August 1912, Lee De Forest, the inventor of the audion, had also observed oscillations in his amplifiers, but he didn't understand its significance and tried to eliminate it^[29][30] until he read Armstrong's patents in 1914,^[31] which he promptly challenged.^[32] Armstrong and De Forest fought a protracted legal battle over the rights to the "regenerative" oscillator circuit^[32][33] which has been called "the most complicated patent litigation in the history of radio".^[34] De Forest ultimately won before the Supreme Court in 1934 on technical grounds, but most sources regard Armstrong's claim as the stronger one.<sup>[30][32]


This was the beginning of radio wave creation in a vacuum tube and propagation.


GOD GAVE US EVERYTHING 

     Ok by 1912, oscillators were made out of vacuum tubes. but the problem was how to keep the frequency stable. Comesd the quartz crystal.</sup>

Crystal oscillator

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Crystal oscillator

A miniature 16 MHz quartz crystal enclosed in a hermetically sealed HC-49/S package, used as the resonator in a crystal oscillator.
Type	Electromechanical
Working principle	Piezoelectricity, Resonance
Invented	Alexander M. Nicholson, Walter Guyton Cady
First production	1918
Electronic symbol

A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a precise frequency.^[1][2][3] This frequency is often used to keep track of time, as in quartz wristwatches, to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio transmitters and receivers. The most common type of piezoelectric resonator used is the quartz crystal, so oscillator circuits incorporating them became known as crystal oscillators,^[1] but other piezoelectric materials including polycrystalline ceramics are used in similar circuits.
A crystal oscillator, particularly one made of quartz crystal, works by being distorted by an electric field when voltage is applied to an electrode near or on the crystal. This property is known as electrostriction or inverse piezoelectricity. When the field is removed, the quartz - which oscillates in a precise frequency - generates an electric field as it returns to its previous shape, and this can generate a voltage. The result is that a quartz crystal behaves like an RLC circuit.
Quartz crystals are manufactured for frequencies from a few tens of kilohertz to hundreds of megahertz. More than two billion crystals are manufactured annually. Most are used for consumer devices such as wristwatches, clocks, radios, computers, and cellphones. Quartz crystals are also found inside test and measurement equipment, such as counters, signal generators, and oscilloscopes.