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Electronics: Magnetic Cores I: Properties 1961 US Army Training Film TF11-3131
"PROPERTIES OF MAGNETIC CORES AND THEIR APPLICATION IN DATA PROCESSING SYSTEM; HOW INFORMATION IS STORED AND TRANSFERRED FROM ONE CORE TO ANOTHER."
US Army Training Film TF11-3131.
Originally a public domain film from the National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).
en.wikipedia.org/wiki/Magnetic-core_memory
Wikipedia license: creativecommons.org/licenses/by-sa/3.0/
Magnetic-core memory was the predominant form of random-access computer memory for 20 years (circa 1955–75). It uses tiny magnetic toroids (rings), the cores, through which wires are threaded to write and read information. Each core represents one bit of information. The cores can be magnetized in two different ways (clockwise or counterclockwise) and the bit stored in a core is zero or one depending on that core's magnetization direction. The wires are arranged to allow an individual core to be set to either a "one" or a "zero", and for its magnetization to be changed, by sending appropriate electric current pulses through selected wires. The process of reading the core causes the core to be reset to a "zero", thus erasing it. This is called destructive readout.
Such memory is often just called core memory, or, informally, core. Although core memory had been superseded by semiconductor memory by the end of the 1970s, memory is still occasionally called "core"; in particular, a file recording the contents of memory after a system error is usually called a core dump...
The basic concept of using the square hysteresis loop of certain magnetic materials as a storage or switching device was known from the earliest days of computer development. Much of this knowledge had developed due to an understanding of transformers, w
US Army Training Film TF11-3131.
Originally a public domain film from the National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).
en.wikipedia.org/wiki/Magnetic-core_memory
Wikipedia license: creativecommons.org/licenses/by-sa/3.0/
Magnetic-core memory was the predominant form of random-access computer memory for 20 years (circa 1955–75). It uses tiny magnetic toroids (rings), the cores, through which wires are threaded to write and read information. Each core represents one bit of information. The cores can be magnetized in two different ways (clockwise or counterclockwise) and the bit stored in a core is zero or one depending on that core's magnetization direction. The wires are arranged to allow an individual core to be set to either a "one" or a "zero", and for its magnetization to be changed, by sending appropriate electric current pulses through selected wires. The process of reading the core causes the core to be reset to a "zero", thus erasing it. This is called destructive readout.
Such memory is often just called core memory, or, informally, core. Although core memory had been superseded by semiconductor memory by the end of the 1970s, memory is still occasionally called "core"; in particular, a file recording the contents of memory after a system error is usually called a core dump...
The basic concept of using the square hysteresis loop of certain magnetic materials as a storage or switching device was known from the earliest days of computer development. Much of this knowledge had developed due to an understanding of transformers, w
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Private-SNAFU_-The-Home-Front-1943-US-Army-Cartoon-Mel-Blanc,-Frank-Tashlin,-World-War-II
Private Snafu imagines the good times his family is having back home while he's stationed in the Arctic. Technical Fairy First Class shows that even his family is helping with the war effort - his dad building tanks, his mom planting a Victory Garden, Grandpa riveting battleships, and his girl joining the WAC's and even the family's horse is pitching in.
This is one of 26 Private SNAFU ('Situation Normal, All Fouled Up) cartoons made by the US Army Signal Corps to educate and boost the morale the troops. Originally created by Theodore Geisel (Dr. Seuss) and Phil Eastman, most of the cartoons were produced by Warner Brothers Animation Studios - employing their animators, voice actors (primarily Mel Blanc) and Carl Stalling's music."
Originally a public domain film slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).
en.wikipedia.org/wiki/Private_Snafu
Wikipedia license: creativecommons.org/licenses/by-sa/3.0/
Private Snafu is the title character of a series of black-and-white American instructional cartoon shorts produced between 1943 and 1945 during World War II. The character was created by director Frank Capra, chairman of the U.S. Army Air Force First Motion Picture Unit, and most were written by Theodor "Dr. Seuss" Geisel, Philip D. Eastman, and Munro Leaf. Although the United States Army gave Walt Disney the first crack at creating the cartoons, Leon Schlesinger of the Warner Bros. animation studio underbid Disney by two-thirds and won the contract. Disney had also demanded exclusive ownership of the character, and merchandising rights. Nel (2007) shows the goal was to help enlisted men with weak literacy skills learn through animated cartoons (and also supplementary comic books). They featured simple l
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How-Magnets-Produce-Electricity-1954-US-Navy-Training-Film-MN-8016b--Electromagnetism-Primer
How Magnets Produce Electricity 1954 US Navy Training Film MN-8016b; Electromagnetism Primer
HOW A MAGNETIC FIELD EFFECTS A SINGLE ATOM, A GROUP OF ATOMS AND A WIRE IN A CLOSED CIRCUIT WITH A METER." Animation produced by Graphic Films for the US Navy.
US Navy training film MN-8016b
Originally a public domain film from the US National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).
en.wikipedia.org/wiki/Electric_generator
Wikipedia license: creativecommons.org/licenses/by-sa/3.0/
...Before the connection between magnetism and electricity was discovered, electrostatic generators were invented that used electrostatic principles. These generated very high voltages and low currents. They operated by using moving electrically charged belts, plates and disks to carry charge to a high potential electrode...
In 1827, Hungarian Anyos Jedlik started experimenting with electromagnetic rotating devices which he called electromagnetic self-rotors. In the prototype of the single-pole electric starter (finished between 1852 and 1854) both the stationary and the revolving parts were electromagnetic. He formulated the concept of the dynamo at least 6 years before Siemens and Wheatstone but didn't patent it as he thought he wasn't the first to realize this. In essence the concept is that instead of permanent magnets, two electromagnets opposite to each other induce the magnetic field around the rotor. It was also the discovery of the principle of self-excitation...
In the years of 1831--1832, Michael Faraday discovered the operating principle of electromagnetic generators. The principle, later called Faraday's law, is that an electromotive force is generated in an electrical conductor that encircles a varying magnetic flux. He also built the first electromagnetic generator, called the Faraday disk, a type of homopolar generator, using a copper disc rotating between the poles of a horseshoe magnet. It produced a small DC voltage.
This design was inefficient due to self-cancelling counterflows of current in regions not under the influence of the magnetic field...
The dynamo was the first electrical generator capable of delivering power for industry. The dynamo uses electromagnetic principles to convert mechanical rotation into pulsed DC through the use of a commutator. The first dynamo was built by Hippolyte Pixii in 1832.
Through a series of accidental discoveries, the dynamo became the source of many later inventions, including the DC electric motor, the AC alternator, the AC synchronous motor, and the rotary converter.
A dynamo machine consists of a stationary structure, which provides a constant magnetic field, and a set of rotating windings which turn within that field. On small machines the constant magnetic field may be provided by one or more permanent magnets; larger machines have the constant magnetic field provided by one or more electromagnets, which are usually called field coils.
Large power generation dynamos are now rarely seen due to the now nearly universal use of alternating current for power distribution and solid state electronic AC to DC power conversion. But before the principles of AC were discovered, very large direct-current dynamos were the only means of power generation and distribution. Now power generation dynamos are mostly a curiosity...
Without a commutator, a dynamo becomes an alternator, which is a synchronous singly fed generator. When used to feed an electric power grid, an alternator must always operate at a constant speed that is precisely synchronized to the electrical frequency of the power grid. A DC generator can operate at any speed within mechanical limits, but always outputs direct current..
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Electronics_-Radar_-Technical-Principles_-Indicators-1946-US-Army-Training-Film-TF11-1387
Electronics: “Radar: Technical Principles: Indicators” 1946 US Army Training Film
Originally a public domain film from the National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and equalization (the resulting sound, though not perfect, is far less noisy than the original).
en.wikipedia.org/wiki/Radar
Wikipedia license: creativecommons.org/licenses/by-sa/3.0/
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio waves or microwaves which bounce off any object in their path. The object returns a tiny part of the wave's energy to a dish or antenna which is usually located at the same site as the transmitter.
Radar was developed in secret in nations across the world just before and during World War II. The term RADAR was coined in 1941 by the United States Navy as an acronym for radio detection and ranging. The term radar has since entered English and other languages as the common noun radar, losing all capitalization...
As early as 1886, Heinrich Hertz showed that radio waves could be reflected from solid objects. In 1895 Alexander Popov, a physics instructor at the Imperial Russian Navy school in Kronstadt, developed an apparatus using a coherer tube for detecting distant lightning strikes...
The German Christian Huelsmeyer was the first to use radio waves to detect "the presence of distant metallic objects". In 1904 he demonstrated the feasibility of detecting a ship in dense fog but not its distance. He obtained a patent for his detection device in April 1904 and later a patent for a related amendment for determining the distance to the ship. He also got a British patent on September 23,
In August 1917 Nikola Tesla outlined a concept for primitive radar units. He stated,
- "...by their [standing electromagnetic waves] use we may produce at will, from a sending station, an electrical effect in any particular region of the globe; [with which] we may determine the relative position or course of a moving object, such as a vessel at sea, the distance traversed by the same, or its speed."
In 1922 A. Hoyt Taylor and Leo C. Young, researchers working with the U.S. Navy, discovered that when radio waves were broadcast at 60 MHz it was possible to determine the range and bearing of nearby ships in the Potomac River. Despite Taylor's suggestion that this method could be used in low visibility, the Navy did not immediately continue the work. Serious investigation began eight years later after the discovery that radar could be used to track airplanes.
Before the Second World War, researchers in France, Germany, Italy, Japan, the Netherlands, the Soviet Union, the United Kingdom, and the United States, independently and in great secrecy, developed technologies that led to the modern version of radar. Australia, Canada, New Zealand, and South Africa followed prewar Great Britain, and Hungary had similar developments during the war.
In 1934 the Frenchman Émile Girardeau stated he was building an obstacle-locating radio apparatus "conceived according to the principles stated by Tesla" and obtained a patent for a working system, a part of which was installed on the Normandie liner in 1935.
During the same year, the Soviet military engineer P.K.Oschepkov, in collaboration with Leningrad Electrophysical Institute, produced an experimental apparatus, RAPID, capable of detecting an aircraft within 3 km of a receiver...
Full radar evolved as a pulsed system, and the first such elementary apparatus was demonstrated in December 1934 by American Robert M. Page, working at the Naval Research Laboratory. The following year, the United States Army successfully tested a primitive surface to surface radar to aim coastal battery search lights at night. This was followed by a pulsed system demonstrated in May 1935 by Rudolf Kühnhold and the firm GEMA in Germany and then one in June 1935 by an Air Ministry team led by Robert A. Watson Watt in Great Britain. Later, in 1943, Page greatly improved radar with the monopulse technique that was used for many years in most radar applications
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Telephone Electronics: “Theory of Simplex and Phantom Circuits: Balanced Conditions” 1944
INTRODUCTION TO SET UP AND PRINCIPLES OF OPERATION - EMPHASIS ON BATTLE IMPORTANCE ."
US Army training film TF11-2062
Originally a public domain film from the US National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).
en.wikipedia.org/wiki/Phantom_circuit
Wikipedia license: creativecommons.org/licenses/by-sa/3.0/
In telecommunication and electrical engineering, a phantom circuit is an electrical circuit derived from suitably arranged wires with one or more conductive paths being a circuit in itself and at the same time acting as one conductor of another circuit.
A phantom group is composed of three circuits that are derived from two single-channel circuits to form a phantom circuit. Here the phantom circuit is a third circuit derived from two suitably arranged pairs of wires, called side circuits, with each pair of wires being a circuit in itself and at the same time acting as one conductor of the third circuit. The "side circuits" within phantom circuits can be coupled to their respective voltage drops by center-tapped transformers, usually called "repeating coils". The center taps are on the line side of the side circuits. Current from the phantom circuit is split evenly by the center taps. This cancels crosstalk from the phantom circuit to the side circuits.
Phantom working increased the number of circuits on long distance routes in the early 20th century without putting up more wires. Phantoming declined with the adoption of carrier systems.
It is theoretically possible to create a phantom circuit from two other phantom circuits and so on up in a pyramid with a maximum 2n-1 circuits being derived from n original circuits. However, more than one level of phantoming is usually impractical. Isolation between the phantom circuit and the side circuits relies on accurate balance of the line and transformers. Imperfect balance results in crosstalk between the phantom and side circuits and this effect accumulates as each level of phantoms is added. Even small levels of crosstalk are unacceptable on analogue telecommunications circuits since speech crosstalk is still intelligible down to quite low levels.
Phantom microphone powering
Recording and broadcast studios commonly use phantom powering as a means to provide power to microphones. Power may be needed either for a device that requires power such as a pre-amp on an electret microphone or because the microphone is a type that intrinsically requires powering such as a condenser microphone. Since the microphone has only one pair of wires the return path for the power has to be provided elsewhere. This is usually done via the microphone cable screen.
DC phantom
Simple DC signalling can be achieved on a telecommunications line in a similar way to phantom powering of microphones. A switch connected to the transformer centre-tap at one end of the line can operate a similarly connected relay at the other end. The return path is through the ground connection. This arrangement can be used for remotely controlling equipment.
Carrier circuit phantoms
From the 1950s to around the 1980s, using phantoms on star-quad trunk carrier circuits was a popular method of deriving a high quality broadcast audio circuit. The multiplexed FDM telecommunications carrier system usually did not use the baseband of the cable because it was inconvenient to separate low frequencies with filters. On the other hand, a one-way audio phantom could be formed from the two pairs (go and return signals) making up the star-quad cable.
Unloaded phantom is a phantom configuration of loaded lines (a circuit fitted with loading coils). The idea here is not to create additional circuits. Rather, the purpose is to cancel or greatly reduce the effect of the loading coils fitted to a line. The reason for doing this is that loaded lines have a definite cut-off frequency and it may be desired to equalise the line to a frequency which is higher than this, for example to make a circuit suitable for use by a broadcaster. Ideally, the loading would be removed or reduced for a permanent connection, but this is not feasible for temporary arrangements such as a requirement for outside broadcast. Instead, two circuits in a phantom configuration can be used to greatly reduce the inductance being inserted by the loading coils, and hence the loading effect.
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Private-SNAFU_-Gas-1944-US-Army-Training-Cartoon-Mel-Blanc--Chuck-Jones
Snafu (Mel Blanc) learns the need of keeping his gas mask at hand when he is attacked by anthropomorphic gas cloud." With a cameo appearance by Bugs Bunny. Directed by Chuck Jones. "Originally created by Theodore Geisel (Dr. Seuss) and Phil Eastman, most of the cartoons were produced by Warner Brothers Animation Studios - employing their animators, voice actors (primarily Mel Blanc) and Carl Stalling's music."
Originally a public domain film from the US National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).
en.wikipedia.org/wiki/Gas_(1944_film)
Wikipedia license: creativecommons.org/licenses/by-sa/3.0/
Gas is an animated short, directed by Chuck Jones and first released in May, 1944. It features Private Snafu learning the value of a gas mask in warfare. The cartoon was produced by Warner Bros. Cartoons. The script writers for the Snafu cartoons were typically uncredited, though animation historians consider that several of them were written or co-written by Dr. Seuss and Munro Leaf...
The film is set in a military camp, with a sign informing viewers that the camp is situated at a distance of 3642,5 miles (5862 kilometers) from Brooklyn. An alarm alerts the soldiers to wear their gas masks and assemble at a predetermined area of the camp. Every soldier rushes to complete the task, except for Snafu who has trouble locating his gas mask case. He is the last soldier to arrive to the assembly grounds, and has yet to actually wear his mask. When Snafu opens the case, he reaches in and retrieves first a sheer bra, then Bugs Bunny, and last his mask. His lack of organization skills earns him the attention of the officers. He is singled out for additional drill exercises with his gas mask.
Following his training, an exhausted Snafu discards his gas mask and leaves it with the trash waiting to be collected. He proceeds to rest under a tree in an idyllic meadow, at a short distance from the camp. While he rests, a passing airplane sprays poison gas. The gas takes the form of an anthropomorphic gas cloud and parachutes its way to the ground. Spotting Snafu as the easiest target around, it begins surrounding him. As Snafu relaxes under the tree, he comments on "the smell of new-mown hay, apple blossoms, flypaper..." whereupon he finally realizes that he is in danger of being gassed.
Snafu barely manages to escape breathing the gas and "frantically chases the trash truck" to retrieve his gas mask. While the gas cloud seems to sweep over both the soldier and the truck, Snafu emerges triumphant. He had managed to wear the mask before breathing the poison. Night finds Snafu sleeping with his gas mask at hand, "in a lover's embrace". In a flirtatious manner, the mask comments "I didn't know you cared" and the short ends.
Analysis
The extensive use of chemical weapons in World War I had left a lasting impression. During World War II, there were fears that chemical warfare would again be used against both military targets and civilians. In practice, all major combatants of the War stockpiled chemical weapons, but these weapons were rarely used and played a minimal role in the conflict.
The short was part of the ongoing efforts of the military to convince soldiers that their gas masks were more than "dead weight". As the war progressed and the expected chemical warfare did not occur, soldiers were increasingly likely to view both the masks and their training in using them as essentially useless.
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Electronics_-Capacitors-1965-US-Air-Force-Training-Film-TV-209
Electronics: “Capacitors” 1965 US Air Force Training Film
DEFINES ELECTROSTATIC FIELD AND DIELECTRIC. DESCRIBES AIR, PAPER, OIL, ELECTROLYTIC, AND CERAMIC TYPE CAPACITORS AS TO THEIR CONSTRUCTION AND GENERAL USAGE. THE UNIT FOR MEASURING CAPACITORS, THE "FARAD", IS STATED AND EXAMPLES OF COMPUTING CAPACITANCE ARE GIVEN. THE FACTORS OF DIELECTRIC, PLATE AREA, AND DISTANCE BETWEEN PLATES WHICH AFFECT THE VALUE OF CAPACITANCE ARE PRESENTED, AND THE NARRATOR DISCUSSES THEIR EFFECTS ON CAPACITANCE. DEFINES VOLTAGE RATING AND EXPLAINS THE FACTORS WHICH AFFECT THE VOLTAGE RATINGS OF CAPACITORS."
United States Air Force Training Film TV-209
Originally a public domain film from the US National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).
en.wikipedia.org/wiki/Capacitor
Wikipedia license: creativecommons.org/licenses/by-sa/3.0/
A capacitor (originally known as condenser) is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric (insulator); for example, one common construction consists of metal foils separated by a thin layer of insulating film. Capacitors are widely used as parts of electrical circuits in many common electrical devices.
When there is a potential difference (voltage) across the conductors, a static electric field develops across the dielectric, causing positive charge to collect on one plate and negative charge on the other plate. Energy is stored in the electrostatic field. An ideal capacitor is characterized by a single constant value, capacitance, measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them.
The capacitance is greatest when there is a narrow separation between large areas of conductor, hence capacitor conductors are often called "plates," referring to an early means of construction. In practice, the dielectric between the plates passes a small amount of leakage current and also has an electric field strength limit, resulting in a breakdown voltage, while the conductors and leads introduce an undesired inductance and resistance.
Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass, in filter networks, for smoothing the output of power supplies, in the resonant circuits that tune radios to particular frequencies, in electric power transmission systems for stabilizing voltage and power flow, and for many other purposes...
In October 1745, Ewald Georg von Kleist of Pomerania in Germany found that charge could be stored by connecting a high-voltage electrostatic generator by a wire to a volume of water in a hand-held glass jar. Von Kleist's hand and the water acted as conductors, and the jar as a dielectric (although details of the mechanism were incorrectly identified at the time). Von Kleist found, after removing the generator, that touching the wire resulted in a painful spark... The following year, the Dutch physicist Pieter van Musschenbroek invented a similar capacitor, which was named the Leyden jar, after the University of Leiden where he worked.
Daniel Gralath was the first to combine several jars in parallel into a "battery" to increase the charge storage capacity. Benjamin Franklin investigated the Leyden jar and "proved" that the charge was stored on the glass, not in the water as others had assumed. He also adopted the term "battery", (denoting the increasing of power with a row of similar units as in a battery of cannon), subsequently applied to clusters of electrochemical cells. Leyden jars were later made by coating the inside and outside of jars with metal foil, leaving a space at the mouth to prevent arcing between the foils. The earliest unit of capacitance was the 'jar', equivalent to about 1 nanofarad.
Leyden jars or more powerful devices employing flat glass plates alternating with foil conductors were used exclusively up until about 1900, when the invention of wireless (radio) created a demand for standard capacitors, and the steady move to higher frequencies required capacitors with lower inductance. A more compact construction began to be used of a flexible dielectric sheet such as oiled paper sandwiched between sheets of metal foil, rolled or folded into a small package
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Telephone-Electronics_-Basic-Telephony-1961-US-Army-Training-Film-TF11-3116
Telephone Electronics: “Basic Telephony” 1961 US Army Training Film TF11-3116
ELECTRO-MAGNETIC THEORY AS APPLIED TO TELEPHONY; COMPONENTS, OPERATION AND TRANSMISSION RANGE OF SOUND POWERED, LOCAL BATTERY, AND COMMON BATTERY TELEPHONIC SYSTEM."
US Army Training Film TF11-3116
Originally a public domain film from the US National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).
en.wikipedia.org/wiki/Telephony
Wikipedia license: creativecommons.org/licenses/by-sa/3.0/
In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other. The technology is associated with the electronic transmission of voice, fax, or other information between distant parties using systems historically associated with the telephone, a hand-held device containing both a speaker or transmitter and a receiver. It is commonly referred to as the construction or operation of telephones or telephonic systems and as a system of telecommunications in which telephonic equipment is employed in the transmission of speech or other sound between points, with or without the use of wires..
To break the term down into further detail, telephony is the science of translating sound into electrical signals, transmitting them, and then converting them back to sound; that is, the science of telephones. The term is used frequently to refer to computer hardware and software that performs functions traditionally performed by telephone equipment. For example, telephony software can combine with your modem to turn your computer into a sophisticated answering service. A popular example of this type of telephony software is voice mail...
Brief overview
Telephones were originally connected directly together in pairs. Each user would have a separate telephone wired to various places he might wish to reach. This became inconvenient when people wanted to communicate with many other people using telephones, so the telephone exchange was invented. Each telephone could then be connected to other local ones, thus inventing the local loop and the telephone call. Soon, nearby exchanges were connected by trunk lines, and eventually distant ones were as well.
In modern times, most telephones are plugged into telephone jacks. The jacks are connected by inside wiring to a drop wire which connects the building to a cable. Cables usually bring a large number of drop wires from all over a district access network to one wire center or telephone exchange. When the user of a telephone wants to make a telephone call, equipment at the exchange examines the dialed telephone number and connects that telephone line to another in the same wire center, or to a trunk to a distant exchange. Most of the exchanges in the world are connected to each other, forming the public switched telephone network (PSTN). By the end of the 20th century almost all were stored program control exchanges.
After the middle of the 20th century, fax and data became important secondary users of the network created to carry voices, and late in the century, parts of the network were upgraded with ISDN and DSL to improve handling of such traffic.
Today, telephony has been digitized and has merged into digital telephony,..
Another important concept that has been merged into telephony is computer telephony integration, which enables computers to know about and control phone functions such as making and receiving voice, fax, and data calls with telephone directory services and caller identification
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APOLL
Apollo-16_-Nothing-So-Hidden-1972-NASA--Fifth-Moon-Landing--John-Young,-Charlie-Duke...
Apollo 16: “Nothing So Hidden” 1972 NASA; Fifth Moon Landing; John Young, Charlie Duke
Apollo 16 was the fifth moon landing of Project Apollo, and the 10th manned mission in the Apollo program. It was the second mission to utilize a Lunar Rover (Lunar Roving Vehicle, LRV) during lunar EVAs (moonwalks). Produced for NASA by A-V Corporation, Houston, Texas.
Commander John W. Young
Lunar Module Pilot Charles M. Duke, Jr.
Command Module Pilot T. Kenneth Mattingly II
Command Module "Casper" CM-113 mass 12,874 pounds (5,840 kg)
Lunar Module "Orion" LM-11 mass 36,729 pounds (16,660 kg)
Launch vehicle Saturn V SA-511
Launch Complex 39A
Launch date April 16, 1972 17:54:00 UTC
Lunar landing April 21, 1972 02:23:35 UTC Descartes Highlands
Lunar EVA duration 1st 07:11:02 2nd 07:23:09 3rd 05:40:03 Total 20:14:14
Lunar surface time 2d 23h 02m 13s
Lunar sample mass 95.71 kg (211 lb)
Total CSM time in lunar orbit 5d 05h 49m 32s
Earth Landing April 27, 1972 19:45:05 UTC South Pacific Ocean
Mission duration 11 d 01 h 51 m 05 s
NASA film JSC-580 aka HQ-222
Originally a public domain film from NASA, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).
en.wikipedia.org/wiki/Apollo_16
Wikipedia license: creativecommons.org/licenses/by-sa/3.0/
Apollo 16 was the tenth manned mission in the United States Apollo space program, the fifth and penultimate to land on the Moon and the first to land in the lunar highlands. The second of the so-called "J missions," it was crewed by Commander John Young, Lunar Module Pilot Charles Duke and Command Module Pilot Ken Mattingly. Launched from the Kennedy Space Center in Florida at 12:54 PM EST on April 16, 1972, the mission lasted 11
days, 1 hour,
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Electronics_-Radar_-Technical-Principles_-Mechanics-1946-US-Army-Training-Film-TF11-1386
Electronics: “Radar: Technical Principles: Mechanics” 1946 US Army Training Film
A US Army training film explaining the basics of Radar systems for radar repairmen.
US Army training film TF11-1386
Originally a public domain film from the US National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).
en.wikipedia.org/wiki/Radar
Wikipedia license: creativecommons.org/licenses/by-sa/3.0/
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio waves or microwaves which bounce off any object in their path. The object returns a tiny part of the wave's energy to a dish or antenna which is usually located at the same site as the transmitter.
Radar was developed in secret in nations across the world just before and during World War II. The term RADAR was coined in 1941 by the United States Navy as an acronym for radio detection and ranging. The term radar has since entered English and other languages as the common noun radar, losing all capitalization...
As early as 1886, Heinrich Hertz showed that radio waves could be reflected from solid objects. In 1895 Alexander Popov, a physics instructor at the Imperial Russian Navy school in Kronstadt, developed an apparatus using a coherer tube for detecting distant lightning strikes. The next year, he added a spark-gap transmitter. In 1897, while testing this in communicating between two ships in the Baltic Sea, he took note of an interference beat caused by the passage of a third vessel. In his report, Popov wrote that this phenomenon might be used for detecting objects, but he did nothing more with this observation.
The German Christian Huelsmeyer was the first to use radio waves to detect "the presence of distant metallic objects". In 1904 he demonstrated the feasibility of detecting a ship in dense fog but not its distance. He obtained a patent for his detection device in April 1904 and later a patent for a related amendment for determining the distance to the ship. He also got a British patent on September 23,
In August 1917 Nikola Tesla outlined a concept for primitive radar units. He stated,
- "...by their [standing electromagnetic waves] use we may produce at will, from a sending station, an electrical effect in any particular region of the globe; [with which] we may determine the relative position or course of a moving object, such as a vessel at sea, the distance traversed by the same, or its speed."
In 1922 A. Hoyt Taylor and Leo C. Young, researchers working with the U.S. Navy, discovered that when radio waves were broadcast at 60 MHz it was possible to determine the range and bearing of nearby ships in the Potomac River. Despite Taylor's suggestion that this method could be used in low visibility, the Navy did not immediately continue the work. Serious investigation began eight years later after the discovery that radar could be used to track airplanes.
Before the Second World War, researchers in France, Germany, Italy, Japan, the Netherlands, the Soviet Union, the United Kingdom, and the United States, independently and in great secrecy, developed technologies that led to the modern version of radar...
In 1934 the Frenchman Émile Girardeau stated he was building an obstacle-locating radio apparatus "conceived according to the principles stated by Tesla" and obtained a patent for a working system, a part of which was installed on the Normandie liner in 1935.
During the same year, the Soviet military engineer P.K.Oschepkov, in collaboration with Leningrad Electrophysical Institute, produced an experimental apparatus, RAPID, capable of detecting an aircraft within 3 km of a receiver...
Full radar evolved as a pulsed system, and the first such elementary apparatus was demonstrated in December 1934 by American Robert M. Page, working at the Naval Research Laboratory. The following year, the United States Army successfully tested a primitive surface to surface radar to aim coastal battery search lights at night. This was followed by a pulsed system demonstrated in May 1935 by Rudolf Kühnhold and the firm GEMA in Germany and then one in June 1935 by an Air Ministry team led by Robert A. Watson Watt in Great Britain. Later, in 1943, Page greatly improved radar with the monopulse technique that was used for many years in most radar applications
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