Stadelheim Prison, in Munich's Giesing district, is one of the largest prisons in Germany. Founded in 1894, it was the site of many executions by guillotine during the Nazi period. Ludwig Thoma, served a six-week prison sentence in 1906 for insulting the morality associations. Kurt Eisner, after the January strike, imprisoned from summer until 14 October 1918. Anton Graf von Arco auf Valley, the assassin of Kurt Eisner, Minister President of Bavaria, he served his sentence in cell 70, in 1924 was evicted from his cell to make way for Adolf Hitler. Gustav Landauer, killed on 2 May 1919. Eugen Leviné, killed on 5 July 1919. Ernst Toller, imprisoned, 1919–1924. Adolf Hitler, imprisoned for a month in 1922 for assaulting Otto Ballerstedt. Ernst Röhm was imprisoned before his execution by Hitler during the Night of the Long Knives. A former SA-Stabschef, he was shot on 1 July 1934 in cell 70. Peter von Heydebreck, a career Nazi and killed by the SS during the Röhm Putsch in 1934. Leo Katzenberger, guillotined on 2 June 1942 for violating the Nazi Rassenschutzgesetz, or Racial Protection Law.
The judge at the infamous Katzenberger Trial, Oswald Rothaug, condemned him despite a lack of evidence. Hans Scholl, member of the White Rose resistance movement, executed on 22 February 1943. Sophie Scholl, member of the White Rose resistance movement. Executed 22 February 1943. Christoph Probst, member of the White Rose, executed on 22 February 1943. Alexander Schmorell, member of the White Rose, executed on 13 July 1943. Kurt Huber, member of the White Rose, executed on 13 July 1943. Willi Graf, member of the White Rose, executed on 12 October 1943. Friedrich Ritter von Lama, Catholic journalist, listening in on Vatican Radio. Murdered in February 1944. Hans Conrad Leipelt, member of the White Rose, executed on 19 January 1945. Ingrid Schubert, member of the Red Army Faction, found hanged in her cell on 13 November 1977. Dieter Zlof, the kidnapper of Richard Oetker, was here until his transfer to Straubing. Konstantin Wecker, musician, 1995 pre-trial detention for cocaine use. Karl-Heinz Wildmoser Sr. former president of the TSV 1860 Munich football team.
Imprisoned circa 2002. MOK, imprisoned 2003-04. Oliver Shanti, imprisoned since 2008. John Demjanjuk, suspected war criminal. Imprisoned 2009. Gerhard Gribkowsky, chief risk officer of Munich-based bank BayernLB, the former chairman of SLEC. Imprisoned 2010. Breno Borges, association football player and former Bayern Munich member. Imprisoned 2012. Beate Zschäpe, accused member of National Socialist Underground, awaiting trial in Munich between 2013 and 2014, March 2013. Size: 14 hectares Capacity of prison: ca. 1,500 prisoners Highest number of prisoners: 9 November 1993 with 1,969 prisoners Executions 1895 to 1927: 14 Executions 1933 to 1945: at least 1,035 Stadelheim Stadelheim
An Alexanderson alternator is a rotating machine invented by Ernst Alexanderson in 1904 for the generation of high-frequency alternating current for use as a radio transmitter. It was one of the first devices capable of generating the continuous radio waves needed for transmission of amplitude modulation by radio, it was used from about 1910 in a few "superpower" longwave radiotelegraphy stations to transmit transoceanic message traffic by Morse code to similar stations all over the world. Although obsolete by the early 1920s due to the development of vacuum-tube transmitters, the Alexanderson alternator continued to be used until World War II, it is on the list of IEEE Milestones as a key achievement in electrical engineering. After radio waves were discovered in 1887, the first generation of radio transmitters, the spark gap transmitters, produced strings of damped waves, pulses of radio waves which died out to zero quickly. By the 1890s it was realized. Efforts were made to invent transmitters that would produce continuous waves, a sinusoidal alternating current at a single frequency.
In an 1891 lecture, Frederick Thomas Trouton pointed out that, if an electrical alternator were run at a great enough cycle speed it would generate continuous waves at radio frequency. Starting with Elihu Thomson in 1889, a series of researchers built high frequency alternators, Nikola Tesla and Pyke, Parsons and Ewing, Siemens, B. G. Lamme, but none was able to reach the frequencies required for radio transmission, above 20 kHz. In 1904, Reginald Fessenden contracted with General Electric for an alternator that generated a frequency of 100,000 hertz for continuous wave radio; the alternator was designed by Ernst Alexanderson. The Alexanderson alternator was extensively used for long-wave radio communications by shore stations, but was too large and heavy to be installed on most ships. In 1906 the first 50-kilowatt alternators were delivered. One was to Reginald Fessenden at Brant Rock, another to John Hays Hammond, Jr. in Gloucester and another to the American Marconi Company in New Brunswick, New Jersey.
Alexanderson would receive a patent in 1911 for his device. The Alexanderson alternator followed Fessenden's rotary spark-gap transmitter as the second radio transmitter to be modulated to carry the human voice; until the invention of vacuum-tube oscillators in 1913 such as the Armstrong oscillator, the Alexanderson alternator was an important high-power radio transmitter, allowed amplitude modulation radio transmission of the human voice. The last remaining operable Alexanderson alternator is at the VLF transmitter Grimeton in Sweden and was in regular service until 1996, it continues to be operated for a few minutes on Alexanderson Day, either the last Sunday in June or first Sunday in July every year. Starting in 1942 four stations were operated by US Navy: the station at Haiku, Hawaii until 1958, Bolinas until 1946, Tuckerton. Two alternators were shipped to Hawaii in 1942, one each from Marion, MA and Bolinas, CA. Haiku received one; the other went to Guam but returned to Haiku after World War 2.
Haiku began operation of the first 200 kW alternator in 1943. The second alternator went into operation at Haiku in 1949. Both alternators were sold for salvage in 1969 to Kreger Company of California; the Marion station was transferred in 1949 to the US Air Force and used until 1957 for the transmission of weather forecasts to the arctic as well as for the Basen to Greenland and Iceland. One of the alternators was scrapped in 1961 and another one was handed over to the US office of standard, it now resides in a Smithsonian Institution warehouse; the two machines in Brazil were never used because of organizational problems there. They were returned to Radio Central after 1946; the Alexanderson alternator works to an AC electric generator, but generates higher-frequency current, in the low frequency radio frequency range. The rotor has no conductive windings or electrical connections; the space between the teeth is filled with nonmagnetic material, to give the rotor a smooth surface to decrease aerodynamic drag.
The rotor is turned at a high speed by an electric motor. The machine operates by variable reluctance; the periphery of the rotor is embraced by a circular iron stator with a C-shaped cross-section, divided into narrow poles, the same number as the rotor has, carrying two sets of coils. One set of coils is energized with direct current and produces a magnetic field in the air gap in the stator, which passes axially through the rotor; as the rotor turns, alternately either an iron section of the disk is in the gap between each pair of stator poles, allowing a high magnetic flux to cross the gap, or else a non-magnetic slot is in the stator gap, allowing less magnetic flux to pass. Thus the magnetic flux through the stator varies sinusoidally at a rapid rate; these changes in flux induce a radio-frequency voltage in a second set of coils on the stator. The RF collector coils are all interconnected by an output transformer, whose secondary winding is connected to the anten
A T-antenna, T-aerial, flat-top antenna, or top-hat antenna is a capacitively loaded monopole wire radio antenna used in the VLF, LF, MF and shortwave bands. T-antennas are used as transmitting antennas for amateur radio stations, long wave and medium wave broadcasting stations, they are used as receiving antennas for shortwave listening. The antenna consists of one or more horizontal wires suspended between two supporting radio masts or buildings and insulated from them at the ends. A vertical wire is connected to the center of the horizontal wires and hangs down close to the ground, connected to the transmitter or receiver. Combined, the two sections form a "T" shape, hence the name; the transmitter power is applied, or the receiver is connected, between the bottom of the vertical wire and a ground connection. The T-antenna functions as a monopole antenna with capacitive top-loading, it was invented during the first decades of radio, in the wireless telegraphy era, before 1920. When the length of the wire segments are shorter than a quarter wavelength of the radio waves, as is typical for use below 1 MHz, the antenna functions as a vertical electrically short monopole antenna with capacitive top-loading.
Because the two horizontal arms of the "T" have equal but oppositely-directed currents in them, which causes the radio waves from them to cancel far from the antenna, because of similar cancelling ground currents, the horizontal wire radiates little radio power. Instead it serves to add capacitance to the top of the antenna; this increases the currents in the upper portion of the vertical wire, increasing the radiation resistance and thus its efficiency, allowing it to radiate more power, or in a receiving antenna be more sensitive to incoming radio signals. The top load wire can increase radiated power by 2 to 4 times for a given base current. However, the antenna is still not as efficient as a full-height λ/4 vertical monopole, has a higher Q and thus a narrower bandwidth. T-antennas are used at low frequencies where it is not practical to build a quarter-wave vertical antenna because of its height, the vertical radiating wire is very electrically short: only a small fraction of a wavelength long, 0.1 λ or less.
An electrically short antenna has a base reactance, capacitive, in transmitting antennas this must be tuned-out by an added loading coil to make the antenna resonant so it can be fed power efficiently. To increase the top-load capacitance, several parallel horizontal wires are used, connected together at the center where the vertical wire attaches; the capacitance does not increase proportionally with the number of wires, because each wire’s electric field is shielded from the ground by its adjacent wires. Since the vertical wire is the actual radiating element, the antenna radiates vertically polarized radio waves in an omnidirectional radiation pattern, with equal power in all azimuthal directions; the axis of the horizontal wire makes little difference. The power is maximum in a horizontal direction or at a shallow elevation angle, decreasing to zero at the zenith; this makes it a good antenna at LF or MF frequencies, which propagate as ground waves with vertical polarization, but it radiates enough power at higher elevation angles to be useful for sky wave communication.
The effect of poor ground conductivity is to tilt the pattern up, with the maximum signal strength at a higher elevation angle. If it is shorter than λ/4 any monopole antenna has a capacitive reactance; the horizontal top section of a T-antenna reduces the capacitive reactance, substituting for a vertical section whose height would be about 2⁄3 its length. In transmitting antennas, to make the antenna resonant so it can be driven efficiently the capacitance must be canceled out by inserting a loading coil the antenna, if the top-section is not long enough to do so; the loading coil is at the base of the antenna, connected between the antenna and its feedline. At medium and low frequencies, the high antenna capacitance and the high inductance of the loading coil compared to its low radiation resistance makes the loaded antenna behave like a high Q tuned circuit, with a narrow bandwidth over which it will remain well matched to the transmission line, when compared to a λ/4 monopole. To operate over a large frequency range the loading coil must be adjustable, adjusted when the frequency is changed to keep the SWR low.
The high Q causes a high voltage on the antenna, maximum at the current nodes at the ends of the horizontal wire Q times the driving-point voltage. The insulators at the ends must be designed to withstand these voltages. In high power transmitters the output power is limited by the onset of corona discharge on the wires. Radiation resistance is the equivalent resistance of an antenna due to its radiation of radio waves. An antenna short compared to a wavelength has a lower radiation resistance; the input power is divided between the radiation resistance and the "ohmic" resistances of the antenna-ground circuit, chiefly the coil and the ground. The resistance in the coil and the ground system must be kept low to minimize the power dissipated in them, it can be seen that at low frequencies the design of the loading co
In electronics, a vacuum tube, an electron tube, or valve or, colloquially, a tube, is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied. The type known as a thermionic tube or thermionic valve uses the phenomenon of thermionic emission of electrons from a heated cathode and is used for a number of fundamental electronic functions such as signal amplification and current rectification. Non-thermionic types, such as a vacuum phototube however, achieve electron emission through the photoelectric effect, are used for such as the detection of light levels. In both types, the electrons are accelerated from the cathode to the anode by the electric field in the tube; the simplest vacuum tube, the diode invented in 1904 by John Ambrose Fleming, contains only a heated electron-emitting cathode and an anode. Current can only flow in one direction through the device—from the cathode to the anode. Adding one or more control grids within the tube allows the current between the cathode and anode to be controlled by the voltage on the grid or grids.
These devices became a key component of electronic circuits for the first half of the twentieth century. They were crucial to the development of radio, radar, sound recording and reproduction, long distance telephone networks, analogue and early digital computers. Although some applications had used earlier technologies such as the spark gap transmitter for radio or mechanical computers for computing, it was the invention of the thermionic vacuum tube that made these technologies widespread and practical, created the discipline of electronics. In the 1940s the invention of semiconductor devices made it possible to produce solid-state devices, which are smaller, more efficient and durable, cheaper than thermionic tubes. From the mid-1960s, thermionic tubes were being replaced with the transistor. However, the cathode-ray tube remained the basis for television monitors and oscilloscopes until the early 21st century. Thermionic tubes still have some applications, such as the magnetron used in microwave ovens, certain high-frequency amplifiers, amplifiers that audio enthusiasts prefer for their tube sound.
Not all electronic circuit valves/electron tubes are vacuum tubes. Gas-filled tubes are similar devices, but containing a gas at low pressure, which exploit phenomena related to electric discharge in gases without a heater. One classification of thermionic vacuum tubes is by the number of active electrodes. A device with two active elements is a diode used for rectification. Devices with three elements are triodes used for switching. Additional electrodes create tetrodes, so forth, which have multiple additional functions made possible by the additional controllable electrodes. Other classifications are: by frequency range by power rating by cathode/filament type and Warm-up time by characteristic curves design by application specialized parameters specialized functions tubes used to display information Tubes have different functions, such as cathode ray tubes which create a beam of electrons for display purposes in addition to more specialized functions such as electron microscopy and electron beam lithography.
X-ray tubes are vacuum tubes. Phototubes and photomultipliers rely on electron flow through a vacuum, though in those cases electron emission from the cathode depends on energy from photons rather than thermionic emission. Since these sorts of "vacuum tubes" have functions other than electronic amplification and rectification they are described in their own articles. A vacuum tube consists of two or more electrodes in a vacuum inside an airtight envelope. Most tubes have glass envelopes with a glass-to-metal seal based on kovar sealable borosilicate glasses, though ceramic and metal envelopes have been used; the electrodes are attached to leads. Most vacuum tubes have a limited lifetime, due to the filament or heater burning out or other failure modes, so they are made as replaceable units. Tubes were a frequent cause of failure in electronic equipment, consumers were expected to be able to replace tubes themselves. In addition to the base terminals, some tubes had an electrode terminating at a top cap.
The principal reason for doing this was to avoid leakage resistance through the tube base for the high impedance grid input. The bases were made with phenolic insulation which performs poorly as an insulator in humid conditions. Other reasons for using a top cap include improving stability by reducing grid-to-anode capacitance, improved high-frequency performance, keeping a high plate voltage away from lower voltages, accommodating one more electrode than allowed by the base. There was an occasional design that had two top cap connections; the earliest vacuum tubes evolved from incandescent light bulbs, containing a filament sealed in an evacuated glass envelope. When hot, the filament releases electrons into the vacuum, a process called thermio
Munich is the capital and most populous city of Bavaria, the second most populous German federal state. With a population of around 1.5 million, it is the third-largest city in Germany, after Berlin and Hamburg, as well as the 12th-largest city in the European Union. The city's metropolitan region is home to 6 million people. Straddling the banks of the River Isar north of the Bavarian Alps, it is the seat of the Bavarian administrative region of Upper Bavaria, while being the most densely populated municipality in Germany. Munich is the second-largest city in the Bavarian dialect area, after the Austrian capital of Vienna; the city is a global centre of art, technology, publishing, innovation, education and tourism and enjoys a high standard and quality of living, reaching first in Germany and third worldwide according to the 2018 Mercer survey, being rated the world's most liveable city by the Monocle's Quality of Life Survey 2018. According to the Globalization and World Rankings Research Institute Munich is considered an alpha-world city, as of 2015.
Munich is a major international center of engineering, science and research, exemplified by the presence of two research universities, a multitude of scientific institutions in the city and its surroundings, world class technology and science museums like the Deutsches Museum and BMW Museum.. Munich houses many multinational companies and its economy is based on high tech, the service sector and creative industries, as well as IT, biotechnology and electronics among many others; the name of the city is derived from the Old/Middle High German term Munichen, meaning "by the monks". It derives from the monks of the Benedictine order, who ran a monastery at the place, to become the Old Town of Munich. Munich was first mentioned in 1158. Catholic Munich resisted the Reformation and was a political point of divergence during the resulting Thirty Years' War, but remained physically untouched despite an occupation by the Protestant Swedes. Once Bavaria was established as a sovereign kingdom in 1806, it became a major European centre of arts, architecture and science.
In 1918, during the German Revolution, the ruling house of Wittelsbach, which had governed Bavaria since 1180, was forced to abdicate in Munich and a short-lived socialist republic was declared. In the 1920s, Munich became home to several political factions, among them the NSDAP; the first attempt of the Nazi movement to take over the German government in 1923 with the Beer Hall Putsch was stopped by the Bavarian police in Munich with gunfire. After the Nazis' rise to power, Munich was declared their "Capital of the Movement". During World War II, Munich was bombed and more than 50% of the entire city and up to 90% of the historic centre were destroyed. After the end of postwar American occupation in 1949, there was a great increase in population and economic power during the years of Wirtschaftswunder, or "economic miracle". Unlike many other German cities which were bombed, Munich restored most of its traditional cityscape and hosted the 1972 Summer Olympics; the 1980s brought strong economic growth, high-tech industries and scientific institutions, population growth.
The city is home to major corporations like BMW, Siemens, MAN, Linde and MunichRE. Munich is home to many universities and theatres, its numerous architectural attractions, sports events and its annual Oktoberfest attract considerable tourism. Munich is one of the fastest growing cities in Germany, it is a top-ranked destination for expatriate location. Munich hosts more than 530,000 people of foreign background; the first known settlement in the area was of Benedictine monks on the Salt road. The foundation date is not considered the year 1158, the date the city was first mentioned in a document; the document was signed in Augsburg. By the Guelph Henry the Lion, Duke of Saxony and Bavaria, had built a toll bridge over the river Isar next to the monk settlement and on the salt route, but as part of the archaeological excavations at Marienhof in advance of the expansion of the S-Bahn from 2012 shards of vessels from the eleventh century were found, which prove again that the settlement Munich must be older than their first documentary mention from 1158.
In 1175 Munich received city fortification. In 1180 with the trial of Henry the Lion, Otto I Wittelsbach became Duke of Bavaria, Munich was handed to the Bishop of Freising. In 1240, Munich was transferred to Otto II Wittelsbach and in 1255, when the Duchy of Bavaria was split in two, Munich became the ducal residence of Upper Bavaria. Duke Louis IV, a native of Munich, was elected German king in 1314 and crowned as Holy Roman Emperor in 1328, he strengthened the city's position by granting it the salt monopoly, thus assuring it of additional income. In the late 15th century, Munich underwent a revival of gothic arts: the Old Town Hall was enlarged, Munich's largest gothic church – the Frauenkirche – now a cathedral, was constructed in only 20 years, starting in 1468; when Bavaria was reunited in 1506, Munich became its capital. The arts and politics became influenced by the court. During the 16th century, Munich was a centre of the German counter reformation, of renaissance arts. Duke Wilhelm V commissioned the Jesuit Michaelskirche, which became a centre for the counter-reform
A broadcast transmitter is a transmitter used for broadcasting, an electronic device which radiates radio waves modulated with information content intended to be received by the general public. Examples are a radio broadcasting transmitter which transmits audio to broadcast radio receivers owned by the public, or a television transmitter, which transmits moving images to television receivers; the term includes the antenna which radiates the radio waves, the building and facilities associated with the transmitter. A broadcasting station consists of a broadcast transmitter along with the production studio which originates the broadcasts. Broadcast transmitters must be licensed by governments, are restricted to specific frequencies and power levels; each transmitter is assigned a unique identifier consisting of a string of letters and numbers called a callsign, which must be used in all broadcasts. In broadcasting and telecommunication, the part which contains the oscillator and sometimes audio processor, is called the "exciter".
Most transmitters use the heterodyne principle, so they have frequency conversion units. Confusingly, the high-power amplifier which the exciter feeds into is called the "transmitter" by broadcast engineers; the final output is given as transmitter power output, although this is not what most stations are rated by. Effective radiated power is used when calculating station coverage for most non-broadcast stations, it is the TPO, minus any attenuation or radiated loss in the line to the antenna, multiplied by the gain which the antenna provides toward the horizon. This antenna gain is important, because achieving a desired signal strength without it would result in an enormous electric utility bill for the transmitter, a prohibitively expensive transmitter. For most large stations in the VHF- and UHF-range, the transmitter power is no more than 20% of the ERP. For VLF, LF, MF and HF the ERP is not determined separately. In most cases the transmission power found in lists of transmitters is the value for the output of the transmitter.
This is shorter. For other aerial types there are gain factors, which can reach values until 50 for shortwave directional beams in the direction of maximum beam intensity. Since some authors take account of gain factors of aerials of transmitters for frequencies below 30 MHz and others not, there are discrepancies of the values of transmitted powers. Transmitters are sometimes fed from a higher voltage level of the power supply grid than necessary in order to improve security of supply. For example, the Allouis and Roumoules transmitters are fed from the high-voltage network though a power supply from the medium-voltage level of the power grid would be able to deliver enough power. Low-power transmitters do not require special cooling equipment. Modern transmitters can be efficient, with efficiencies exceeding 98 percent. However, a broadcast transmitter with a megawatt power stage transferring 98% of that into the antenna can be viewed as a 20 kilowatt electric heater. For medium-power transmitters up to a several tens of kilowatts, including 50 kW AM and 20 kW FM, forced air cooling is used.
At power levels above these some transmitters have the output stage cooled by a forced liquid cooling system analogous to an automobile cooling system. Since the coolant directly touches the high-voltage anodes of the tubes, only distilled, deionised water or a special dielectric coolant can be used in the cooling circuit; this high-purity coolant is in turn cooled by a heat exchanger, where the second cooling circuit can use water of ordinary quality because it is not in contact with energized parts. Very-high-power tubes of small physical size may use evaporative cooling by water in contact with the anode; the production of steam allows a high heat flow in a small space. The high voltages used in high power transmitters require extensive protection equipment. Transmitters are exposed to damage from lightning. Transmitters may be damaged if operated without an antenna, so protection circuits must detect the loss of the antenna and switch off the transmitter immediately. Tube-based transmitters must have power applied in the proper sequence, with the filament voltage applied before the anode voltage, otherwise the tubes can be damaged.
The output stage must be monitored for standing waves, which indicate that generated power is not being radiated but instead is being reflected back into the transmitter. Lightning protection is required between the antenna; this consists of spark gaps and gas-filled surge arresters to limit the voltage that appears on the transmitter terminals. The control instrument that measures the voltage standing-wave ratio switches the transmitter off if a higher voltage standing-wave ratio is detected after a lightning strike, as the reflections are due to lightning damage. If this does not succeed after several attempts, the antenna may be damaged and the transmitter should remain switched off. In some transmitting plants UV detectors are fitted in critical places, to switch off the transmitter if an arc is detected; the operating voltages, modulation factor and other transmitter parameters are monitored for protection and diagnostic purposes, may be displayed locally and/or at a remote control room.
A commercial transmitter site will have a control building to shelter the transmitter components and control devices. This is a purely functional building, which may contain ap
The Lorenz SZ40, SZ42a and SZ42b were German rotor stream cipher machines used by the German Army during World War II. They were developed by C. Lorenz AG in Berlin; the model name SZ was derived from Schlüssel-Zusatz. The instruments implemented a Vernam stream cipher. British cryptanalysts, who referred to encrypted German teleprinter traffic as Fish, dubbed the machine and its traffic Tunny and deduced its logical structure three years before they saw such a machine; the SZ machines were in-line attachments to standard teleprinters. An experimental link using SZ40 machines was started in June 1941; the enhanced SZ42 machines were brought into substantial use from mid-1942 onwards for high-level communications between the German High Command in Wünsdorf close to Berlin, Army Commands throughout occupied Europe. The more advanced SZ42A came into routine use in February 1943 and the SZ42B in June 1944. Radioteletype rather than land-line circuits was used for this traffic; these non-Morse messages were picked up by Britain's Y-stations at Knockholt and Denmark Hill and sent to Government Code and Cypher School at Bletchley Park.
Some were deciphered using hand methods before the process was automated, first with Robinson machines and with the Colossus computers. The deciphered Lorenz messages made one of the most significant contributions to British Ultra military intelligence and to Allied victory in Europe, due to the high-level strategic nature of the information, gained from Lorenz decrypts. After the Second World War a group of British and US cryptanalysts entered Germany with the front-line troops to capture the documents and personnel of the various German signal intelligence organizations before these secrets could be destroyed, looted, or captured by the Soviets, they were called the Target Intelligence Committee TICOM. From captured German cryptographers Drs Huttenhain and Fricke they learnt of the development of the SZ40 and SZ42 a/b; the design was for a machine. The first machine was referred to as the SZ40, it was recognised. The definitive SZ40 had twelve rotors with movable cams; the rightmost five rotors were named the Chi wheels by Bill Tutte.
The leftmost five were named Psi wheels to Tutte. The middle two Vorgeleger rotors were called motor wheels by Tutte; the five data bits of each ITA2-coded telegraph character were processed first by the five chi wheels and further processed by the five psi wheels. The cams on the wheels reversed the value of a bit if in the raised position, but left it unchanged if in the lowered position. Gilbert Vernam was an AT&T Bell Labs research engineer who, in 1917, invented a cipher system that used the Boolean "exclusive or" function, symbolised by ⊕; this is represented by the following "truth table", where 1 represents "true" and 0 represents "false". Other names for this function are: modulo 2 addition and modulo 2 subtraction. Vernam's cipher is a Symmetric-key algorithm, i.e. the same key is used both to encipher plaintext to produce the ciphertext and to decipher ciphertext to yield the original plaintext: plaintext ⊕ key = ciphertextand: ciphertext ⊕ key = plaintextThis produces the essential reciprocity that allows the same machine with the same settings to be used for both enciphering and deciphering.
Vernam's idea was to use conventional telegraphy practice with a paper tape of the plaintext combined with a paper tape of the key. Each key tape would have been unique, but generating and distributing such tapes presented considerable practical difficulties. In the 1920s four men in different countries invented rotor cipher machines to produce a key stream to act instead of a tape; the 1940 Lorenz SZ40/42 was one of these. The logical functioning of the Tunny system was worked out well before the Bletchley Park cryptanalysts saw one of the machines—which only happened in 1945, shortly before the allied victory in Europe; the SZ machine served as an in-line attachment to a standard Lorenz teleprinter. It was 17 in high; the teleprinter characters consisted of five data bits, encoded in the International Telegraphy Alphabet No. 2. The machine generated a stream of pseudorandom characters; these formed the key, combined with the plaintext input characters to form the ciphertext output characters.
The combination was by means of the XOR process. The key stream consisted of two component parts; these were generated by two sets of five wheels. The Bletchley Park cryptanalyst Bill Tutte called these the χ wheels, the ψ wheels; each wheel had a series of cams around their circumference. These cams could be set in a lowered position. In the raised position they generated a'1' which reversed the value of a bit, in the lowered position they generated a'0' which left the bit unchanged; the number of cams on each wheel equalled the number of impulses needed to cause them to complete a full rotation. These numbers are all co-prime with each other, giving the longest possible time before the pattern repeated; this is the product of the number of positions of the wheels. For the set of χ wheels it was 41 × 31 × 29 × 26 × 23 = 22,041,682 and for the ψ wheels it was 43 × 47 × 51 × 53 × 59 = 3,223,303,017; the set of five χ wheels all moved on one position. The five ψ wheels, advanced intermittently, their movemen