4356M Bottle Transmitter

The 4356M bottle transmitter (B.T.) did not emit any radio frequencies. This device was used to provide transmission to a group of repeater motors, such as those in a radar installation, or to step up the number of repeaters that can be controlled from a gyro-compass where it is inconvenient to use a multiple transmitter or transmitter panel. They were also used extensively where it was desired to use Admiralty type equipment controlled by some other type of gyro compass. Bottle transmitters fell into two groups: 1) pattern #5356 that transmitted to M-type repeater motors; 2) pattern #5355 that transmitted to Sperry-type repeater motors. The B.T. could operate a load equivalent to fifteen Mark 10 M-type repeater motors at its maximum. On HMCS HAIDA, the bottle transmitter was used to transmit azimuth information from the Admiralty Mk 5 Gyrocompass to remote indicators.

Doppler Effect

The Doppler effect is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession. Doppler effect phenomenon was named after Austrian physicist Christian Doppler who proposed it in 1842.

The relative increase in frequency can be explained as follows. When the source of the waves is moving toward the observer, each successive wave crest is emitted from a position closer to the observer than the previous wave. Therefore each wave takes slightly less time to reach the observer than the previous wave. Therefore the time between the arrival of successive wave crests is reduced, causing an increase in the frequency. While they are traveling, the distance between successive wavefronts is reduced; so the waves "bunch together". Conversely, if the source of waves is moving away from the observer, each wave is emitted from a position farther from the observer than the previous wave, so the arrival time between successive waves is increased, reducing the frequency.

In astronomy, the Doppler effect was originally studied in the visible part of the electromagnetic spectrum. Today, the Doppler shift, as it is also known, applies to electromagnetic waves in all portions of the spectrum. Also, because of the inverse relationship between frequency and wavelength, Doppler effect can be discribed in terms of wavelength. Radiation is redshifted when its wavelength increases, and is blueshifted when its wavelength decreases.

Astronomers use Doppler effects to calculate precisely how fast stars and other astronomical objects move toward or away from Earth. For example the spectral lines emitted by hydrogen gas in distant galaxies is often observed to be considerably redshifted. The spectral line emission, normally found at a wavelength of 21 centimeters on Earth, might be observed at 21.1 centimeters instead. This 0.1 centimeter redshift would indicate that the gas is moving away from Earth at over 1,400 kilometers per second (over 880 miles per second).

Superheterodyne Receiver

A superheterodyne receiver is an electronic device which uses frequency mixing to convert a received signal to a fixed intermediate frequency, which can be more conveniently processed than the original radio carrier frequency. Virtually all modern radio and television receivers use the superheterodyne principle. The superheterodyne receiver has three elements: the local oscillator, a frequency mixer that mixes the local oscillator's signal with the received signal, and a tuned amplifier.

Reception starts with an antenna signal, optionally amplified, including the frequency the user wishes to tune, fd. The local oscillator is tuned to produce a frequency close to fd, fLO. The received signal is mixed with the local oscillator signal. This stage does not just linearly add the two inputs, like an audio mixer. Instead it multiplies the input by the local oscillator, producing four frequencies in the output; the original signal, the original fLO, and the two new frequencies fd+fLO and fd-fLO. The output signal also generally contains a number of undesirable mixtures as well. These are 3rd- and higher-order intermodulation products. If the mixing were performed as a pure, ideal multiplication, the original fd and fLO would also not appear; in practice they do appear because mixing is done by a nonlinear process that only approximates true ideal multiplication.

The amplifier portion of the system is tuned to be highly selective at a single frequency, fIF. By changing fLO, the resulting fd-fLO (or fd+fLO) signal can be tuned to the amplifier's fIF. In typical amplitude modulation ("AM radio" in the U.S., or MW) receivers, that frequency is 455 kHz; for FM receivers, it is usually 10.7 MHz; for television, 45 MHz. Other signals from the mixed output of the heterodyne are filtered out by the amplifier.

The original heterodyne technique was pioneered by Canadian inventor Reginald Fessenden, but it was not pursued far because local oscillators available at the time were unstable in their frequency output, and vacuum tubes were not yet available. The superheterodyne principle was revisited in 1918 by U.S. Army Major Edwin Armstrong in France during World War I. He invented this receiver as a means of overcoming the deficiencies of early vacuum tube triodes used as high-frequency amplifiers in radio direction finding equipment.

Effective Radiated Power

Effective radiated power (ERP) is the product of antenna input power and antenna power gain, expressed in kilowatts. In other words, ERP is the power supplied to an antenna multiplied by the antenna gain in a given direction. If the direction is not specified, the direction of maximum gain is assumed. The type of reference antenna must be specified. The product of the power supplied to the antenna and its gain relative to a half-wave dipole in a given direction. If the direction is not specified, the direction of maximum gain is assumed.

Effective radiated power takes into consideration transmitter power output (TPO), transmission line attenuation (electrical resistance and RF radiation), RF connector insertion losses, and antenna directivity, but not height above average terrain (HAAT). ERP is typically applied to antenna systems.

Reflex Klystron

The reflex klystron is a microwave and radio frequency amplifier. It consists of a vacuum tube where the electron beam passes through a single resonant cavity. In the reflex klystron, the electrons are fired into one end of the tube by an electron gun. After passing through the resonant cavity they are reflected by a negatively charged reflector electrode for another pass through the cavity, where they are then collected. The electron beam is velocity modulated when it first passes through the cavity. The formation of electron bunches takes place in the drift space between the reflector and the cavity.

The voltage on the reflector must be adjusted so that the bunching is at a maximum as the electron beam re-enters the resonant cavity, thus ensuring a maximum of energy is transferred from the electron beam to the RF oscillations in the cavity. The voltage should always be switched on before providing the input to the reflex klystron as the whole function of the reflex klystron would be destroyed if the supply is provided after the input. The reflector voltage may be varied slightly from the optimum value, which results in some loss of output power, but also in a variation in frequency. This effect is used to good advantage for automatic frequency control in receivers, and in frequency modulation for transmitters. The level of modulation applied for transmission is small enough that the power output essentially remains constant. At regions far from the optimum voltage, no oscillations are obtained at all. This tube is called a reflex klystron because it repels the input supply or performs the opposite function of a klystron.

There are often several regions of reflector voltage where the reflex klystron will oscillate; these are referred to as modes. The electronic tuning range of the reflex klystron is usually referred to as the variation in frequency between half power points—the points in the oscillating mode where the power output is half the maximum output in the mode. The frequency of oscillation is dependent on the reflector voltage, and varying this provides a crude method of frequency modulating the oscillation frequency, albeit with accompanying amplitude modulation as well. Modern semiconductor technology has effectively replaced the reflex klystron in most applications.

Traveling Wave Tube

A traveling wave tube is an elongated vacuum tube with an electron gun used as a microwave amplifier. A broadband traveling wave tube can have a bandwidth that exceeds an octave, being capable of gains greater than 40 dB. A magnetic containment field around the tube focuses the electrons into a beam, which then passes down the middle of a wire helix that stretches from the RF input to the RF output, the electron beam finally striking a collector at the other end. A directional coupler, which can be either a waveguide or an electromagnetic coil, fed with the low-powered radio signal that is to be amplified, is positioned near the emitter, and induces a current into the helix.

The helix acts as a delay line, in which the RF signal travels at near the same speed along the tube as the electron beam. The electromagnetic field due to the RF signal in the helix interacts with the electron beam, causing bunching of the electrons (an effect called velocity modulation), and the electromagnetic field due to the beam current then induces more current back into the helix (i.e. the current builds up and thus is amplified as it passes down). A second directional coupler, positioned near the collector, receives an amplified version of the input signal from the far end of the helix. An attenuator placed on the helix, usually between the input and output helices, prevents reflected wave from traveling back to the cathode.

The essential principle of operation of a traveling wave tube lies in the interaction between an electron beam and an radio frequency signal. The velocity, v, of an electron beam is given by:

An anode voltage of 5 kV gives an electron velocity of 4.2 x 10*7 mso*-1. The signal would normally travel at c, the velocity of light (3x10*8 ms*-1), which is much faster than any 'reasonable' electron beam (relativistic effects mean that the electron mass actually increases as its velocity approaches c, so that achieving electron velocities approaching c is a complicated business), If, however, the signal can be slowed down to the same velocity as the electron beam, it is possible to obtain amplification of the signal by virtue of its interaction with the beam. This is usually achieved using the helix electrode, which is simply a spiral of wire around the electron beam.

Without the helix, the signal would travel at a velocity c. With the helix, the axial signal velocity is approximately c x (p /2pa) where a, p are shown above, so the signal is slowed by the factor p/2pa. Note that this is independent of signal frequency. The signal travelling along the helix is known as a slow wave, and the helix is referred to as a slow-wave structure, The condition for equal slow-wave and electron-beam velocities is therefore approximately.

Two Cavity Klystron

In the two cavity klystron, the electron beam is injected into a resonant cavity. The electron beam, accelerated by a positive potential, is constrained to travel through a cylindrical drift tube in a straight path by an axial magnetic field. While passing through the first cavity, the electron beam is velocity modulated by the weak RF signal. In the moving frame of the electron beam, the velocity modulation is equivalent to a plasma oscillation. Plasma oscillations are rapid oscillations of the electron density in conducting media such as plasmas or metals. The frequency only depends weakly on the wavelength. So in a quarter of one period of the plasma frequency, the velocity modulation is converted to density modulation, i.e. bunches of electrons. As the bunched electrons enter the second cavity they induce standing waves at the same frequency as the input signal. The signal induced in the second cavity is much stronger than that in the first.

Klystron

A klystron is a linear-beam vacuum tube which is used as a powerful microwave amplifier which produces both low-power reference signals for superheterodyne radar receivers. It also generates high-power carrier waves for communications and the driving force for modern particle accelerators. Klystron amplifiers coherently amplify a reference signal so its output may be precisely controlled in amplitude, frequency and phase. Many klystrons have a waveguide for coupling microwave energy into and out of the device, although it is also quite common for lower power and lower frequency klystrons to use coaxial couplings instead. In some cases a coupling probe is used to couple the microwave energy from a klystron into a separate external waveguide. All modern klystrons are amplifiers, since reflex klystrons, which were used as oscillators in the past, have been surpassed by alternative technologies.

A klystron amplifies RF signals by converting the kinetic energy in a DC electron beam into radio frequency power. A beam of electrons is produced by a thermionic cathode (a heated pellet of low work function material), and accelerated by high-voltage electrodes (typically in the tens of kilovolts). This beam is then passed through an input cavity. RF energy is fed into the input cavity at, or near, its natural frequency to produce a voltage which acts on the electron beam. The electric field causes the electrons to bunch: electrons that pass through during an opposing electric field are accelerated and later electrons are slowed, causing the previously continuous electron beam to form bunches at the input frequency. To reinforce the bunching, a klystron may contain additional "buncher" cavities. The RF current carried by the beam will produce an RF magnetic field, and this will in turn excite a voltage across the gap of subsequent resonant cavities. In the output cavity, the developed RF energy is coupled out. The spent electron beam, with reduced energy, is captured in a collector.

Thrust Vector Control

Thrust vector control, or thrust vectoring, is the capacity of a jet engine to shift the direction of the engine thrust to control the angular velocity of an aircraft or rocket. In ballistic missiles that fly outside the atmosphere thrust vector control is the primary means of orientation control.

Thrust vectoring was originally conceived to provide upward vertical thrust as a means to give aircraft vertical or short takeoff and landing ability. Subsequently, it was realized that using vectored thrust in combat situations enabled aircraft to perform various maneuvers not available to conventional-engined planes. To perform turns, aircraft that use no thrust vectoring must rely on only aerodynamic control surfaces, such as ailerons or flaps; craft with vectoring must still use control surfaces, but to a lesser extent.

Operational vectored thrust aircraft use turbofans with rotating nozzles or vanes to deflect the exhaust stream. This method can successfully deflect thrust through as much as 90 degrees, relative to the aircraft centerline. However, the engine must be sized for vertical lift, rather than normal flight, which results in a weight penalty. Afterburning (or Plenum Chamber Burning, PCB, in the bypass stream) is difficult to incorporate and is impractical for take-off and landing thrust vectoring, because the very hot exhaust can damage runway surfaces. Without afterburning it is hard to reach supersonic flight speeds. The best known example of thrust vectoring is the Rolls-Royce Pegasus engine used in the Hawker Siddeley Harrier, as well as in the AV-8B Harrier II variant.

Widespread use of thrust vectoring for enhanced maneuverability in Western production-model fighter aircraft would have to wait until the 21st century, and the deployment of the Lockheed Martin F-22 Raptor fifth-generation jet fighter, with its afterburning, thrust-vectoring Pratt & Whitney F119 turbofan.

Thrust vector control for many liquid rockets is achieved by gimballing the rocket engine. This often involves moving the entire combustion chamber and outer engine bell, or even the entire engine assembly including the related fuel and oxidizer pumps. Such a system was used on the Saturn V and is employed on the space shuttle.

Thrust vectoring on an F-22

Electron Energy Loss Spectroscopy

Electron Energy Loss Spectroscopy is an analytical technique which involves the measurement of the energy of electrons which have interacted with the specimen, in order to determine their energy loss and hence deduce the nature of the atoms with which they have interacted. In electron energy loss spectroscopy a material is exposed to a beam of electrons with a known, narrow range of kinetic energies. Some of the electrons will undergo inelastic scattering, which means that they lose energy and have their paths slightly and randomly deflected. The amount of energy loss can be measured via an electron spectrometer and interpreted in terms of what caused the energy loss. Inelastic interactions include phonon excitations, inter and intra band transitions, plasmon excitations, inner shell ionizations, and Cerenkov radiation.

Spectral Reflectance

Spectral reflectance is the fraction of incident radiation reflected by a non-transparent surface. Spectral reflectance must be treated as a directional property that is a function of the reflected direction, the incident direction, and the incident wavelength. However it is also commonly averaged over the reflected hemisphere to give the hemispherical spectral reflectivity:Spectral reflectance measures the fractional amplitude of the reflected electromagnetic field, while reflectance refers to the fraction of incident electromagnetic power that is reflected at an interface. The reflectance is thus the square of the magnitude of the reflectivity. The spectral reflectance can be expressed as a complex number as determined by the Fresnel Equations for a single layer, whereas the reflectance is always a positive real number.

The fraction of energy reflected at a particular wavelength varies for different features. Additionally, the reflectance of features varies at different wavelengths. Thus, two features that are indistinguishable in one spectral range may be very different in another portion of the spectrum. This is an essential property of matter that allows for different features to be identified and separated by their spectral signatures. A spectral signature is a unique reflectance value in a specific part of the spectrum.

Uncertainty Principle

The uncertainty principle states that the product of the uncertainty in measurement of one variable, say momentum p, multiplied by the uncertainty of measurement of another variable, say position x, can never be smaller than Planck's constant h. Then Δp Δx = h. So, if we know the position of a particle very accurately we cannot determine its momentum with great precision. The same relationship occurs between other pairs of variables such as energy and time.

The uncertainty principle was postulated by the German physicist Werner Heisenberg, who asserted that certain pairs of physical properties, like position and momentum, cannot both be known to arbitrary precision. That is, the more precisely one property is known, the less precisely the other can be known. It is impossible to measure simultaneously both position and velocity of a microscopic particle with any degree of accuracy or certainty. Heisenberg formulated the uncertainty principle in Niels Bohr's institute at Copenhagen, while working on the mathematical foundations of quantum mechanics.

Schrödinger Equation

The Schrödinger equation is an equation that describes how the quantum state of a physical system changes in time. It is as central to quantum mechanics as Newton's laws are to classical mechanics. The Schrödinger equation can be mathematically transformed into Heisenberg's matrix mechanics, and into Feynman's path integral formulation. The Schrödinger equation describes time in a way that is inconvenient for relativistic theories, a problem which is not as severe in Heisenberg's formulation and completely absent in the path integral.

In the standard interpretation of quantum mechanics, the quantum state is the most complete description which can be given to a physical system. Solutions to Schrödinger's equation describe not only atomic and subatomic systems, atoms and electrons, but also macroscopic systems, possibly even the whole universe. The equation is named after Erwin Schrödinger, who constructed it in 1926.

The Schrödinger equation describes the behaviour of an electron of energy E in a potential V in terms of the wave function y. The time-independent, one-dimensional form of the equation is: d2y/dx2 + (8p2m/h2)[E - V]y = 0 where m is the electron mass and h is Planck's constant.

Electrolytic Process

The electrolytic process is the process that proceeds when an electrical charge is put on between two electrodes in a conducting electrolyte. Some examples of electrolytic aluminium surface treatments are anodising, AC-electrolytic graining and plating. Electrolytic process is the use of electrolysis in industry to refine metals or compounds at a high purity and low cost. Some examples are the Hall-Héroult process used for aluminium, or the production of hydrogen from water. Electrolysis is usually done in bulk using hundreds of sheets of metal connected to an electric power source.

Electrical Conductivity

Electrical conductivity is the capacity of matter to conduct an electric current, indicating the ease with which electrical current flows through it. When an electrical potential difference is placed across a conductor, its movable charges flow, giving rise to an electric current. The conductivity σ is defined as the ratio of the current density J to the electric field strength E.

A conductor such as a metal has high electrical conductivity and a low resistivity. An insulator like glass or plastic has low conductivity and a high resistivity. Silver, copper, gold, and aluminum have the highest electrical conductivity.

Diffraction

Diffraction is an interference effect which leads to the scattering of strong beams of radiation in specific directions. Diffraction usually refers to various phenomena which occur when a wave encounters an obstacle. It is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings. Diffraction from crystals is described by the Bragg Law: n λ= 2 d sin θ; where n is an integer (the order of scattering), λ is the wavelength of the radiation, d is the spacing between the scattering entities (e.g. planes of atoms in the crystal) and θ is the angle of scattering.

Electron and X-ray diffraction are both particularly powerful because their wavelengths are smaller than the typical spacings of atoms in crystals and strong, easily measurable, diffraction occurs. The effects of diffraction can be regularly seen in everyday life. The most colorful examples of diffraction are those involving light; for example, the closely spaced tracks on a CD or DVD act as a diffraction grating to form the familiar rainbow pattern we see when looking at a disk.

Refraction

Refraction is the change in direction of a beam of light. Refraction occurs when a light ray changes mediums. This is most commonly observed when a ray or beam of light passes from one medium to another, as when light traveling from air goes into water. The speed of the light beam changes when it changes mediums, and so does the direction of the light beam.

If someone half-submerges a pencil into a glass of water, he will notice that the straight pencil appears bent at the point it gets into the water. This optical effect is caused by refraction. When light passes from one transparent medium to another, it changes speed, and bends. How much it appears to bend depends on the refractive index of the mediums and the angle between the light ray and the line perpendicular (normal) to the surface separating the two mediums.

In 1621, Willebrord Snell, a Dutch physicist, derived the relationship between the different angles of light as it passes from one transperent medium to another. When light passes from one transparent medium to another, it bends according to Snell's law which states: Ni * Sin(Ai) = Nr * Sin(Ar). where: Ni is the refractive index of the medium the light is leaving; Ai is the incident angle between the light ray and the normal to the meduim to medium interface; Nr is the refractive index of the medium the light is entering; Ar is the refractive angle between the light ray and the normal to the meduim to medium interface.

Refraction

Dark Matter

Dark matter is hypothetical matter which can not be detected by its emitted radiation. Its presence can only be inferred from gravitational effects on visible matter. The flat rotation curves of spiral galaxies and other evidence of "missing mass" in the universe is due to dark matter.

Dark matter accounts for the rotational speeds of galaxies, orbital velocities of galaxies in clusters, gravitational lensing of background objects by galaxy clusters such as the Bullet Cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies, playing a central role in galaxy evolution. It also has measurable effects on the anisotropy of the cosmic microwave background. All these lines of evidence suggest that galaxies, clusters of galaxies, and the universe as a whole contain far more matter than that which interacts with electromagnetic radiation.

The dark matter component has much more mass than the visible component of the universe. At present, the density of ordinary baryons and radiation in the universe is estimated to be equivalent to about one hydrogen atom per cubic meter of space. Only about 4% of the total energy density in the universe can be seen directly. About 22% is thought to be composed of dark matter.

Magnetohydrodynamics

Magnetohydrodynamics is the scientific discipline which studies the dynamics of electrically conducting fluids, which include liquid metals, plasmas, and salt water. The field of magnetohydrodynamics was started by Hannes Alfvén, who was awarded the Nobel Prize in Physics in 1970.

The idea of magnetohydrodynamics is that magnetic fields can induce currents in a moving conductive fluid, creating forces on the fluid, and changing the magnetic field itself. The set of equations which describe magnetohydrodynamics are a combination of the Navier-Stokes equations of fluid dynamics and Maxwell's equations of electromagnetism. These differential equations must to be solved simultaneously, either analytically or numerically.

Galvanometer

A galvanometer is an instrument which is used to detect and measure small electric currents. It functions by the deflection of a magnetic compass needle by a current-carrying coil in a magnetic field.

Galvanometer mechanisms are utilized to position the pens of analog chart recorders like those used for making an electrocardiogram. Strip chart recorders with galvanometer driven pens have a full scale frequency response of 100 Hz and several centimeters deflection.