Very high frequency - Very high frequency Very high frequency (VHF) is the radio frequency range from 30 MHz (wavelength 10 m) to 300 MHz (wavelength 1 m). Common uses for VHF are FM radio broadcast at 88-108 MHz and television broadcast (together with UHF). The general description of frequencies immediately below VHF is HF, and the next higher frequencies as known as Ultra high frequency (UHF). UHF and VHF are the most common frequency bands for television. VHF frequencies' propagation characteristics are ideal for short-distance terrestrial communication. Unlike HF frequencies, the ionosphere does not reflect VHF radio (except on rare occasions during solar flares) and thus transmissions are restricted to the local area (and can't interfere with transmissions thousands of kilometres away) It is also less affected by atmospheric.
Ultra high frequency - Ultra high frequency Ultra high frequency (UHF) radio frequencies are those between 300 MHz and 3.0 GHz, which is higher than those of very high frequency (VHF). UHF and VHF are the most common frequency bands for television. On December 29, 1949 KC2XAK of Bridgeport, Connecticut became the first UHF television station to operate on a regular daily schedule. In Britain, UHF television began with the launch of BBC TWO in 1964. BBC ONE and ITV soon followed, and colour was introduced on UHF only in 1967 - 1969. Today all British terrestrial television channels (both analog and digital) are on UHF. UHF frequencies have higher attenuation from atmospheric moisture and benefit less from 'bounce', or the reflection of signals off the ionosphere back to earth, when.
High-speed rail - High-speed rail High-speed rail is public transport by rail with a possible speed above 200 km/h (125 miles per hour). Typically high speed trains travel at top service speeds of between 250 km/h (150 mph) to 300 km/h (180 mph). Although the world speed record for a wheeled train was set in 1990 by a French TGV which reached a speed of 515 km/h (320 mph), the experimental Japanese magnetic levitation train has reached 581 km/h. Table of contents showTocToggle("show","hide") 1 History 2 High-speed trains vs. automobiles or airplanes 3 Markets for high-speed train 4 High-speed trains in the U.S. 5 High-speed trains in Japan 6 Technology 7 Existing high-speed rail systems History Railways were the first form of mass transportation, and until the invention of.
Frequency synthesiser - Frequency synthesiser A frequency synthesiser is an electronic system for generating any of a range of frequencies from a single fixed timebase or oscillator. They are found in many modern devices, including radio receivers, mobile telephones, radiotelephones, walkie-talkies, CB radios, Satellite receivers, GPS systems, etc. Before the invention of the frequency synthesiser, radio transmitters and receivers had to employ a separate crystal for each channel that the device could operate on. When the user changed channel, a new crystal was switched into the circuit. Since quartz crystals are highly precise they are therefore expensive to make, and in addition take up quite a large amount of space. Frequency synthesisers generate multiple channels from a single master crystal oscillator, and can generate hundreds of frequencies. This yields.
Frequency response - Frequency response Frequency response is the measure of any system's response to frequency, but is usually used in connection with electronic amplifiers and similar systems, particularly in relation to audio signals. For example, a high fidelity amplifier may be said to have a frequency response of 20Hz - 20,000Hz ±1dB, which tells you that the system responds equally to all frequencies within that range and within the limits quoted. As such it is not a measure that is very useful in terms of the quality of reproduction, only that it fulfils the basic requirements needed for it. A related term is bandwidth, but that has both a more tightly defined meaning, and a broader application..
Radio frequency - Radio frequency Radio frequency, or RF, is a carrier, or alternating current with or without a signal, at a frequency that can radiate, or propagate, if not shielded. Such frequencies account for the following parts of the electromagnetic spectrum: Very low frequency (VLF): 3-30 kHz Low frequency (LF): 30-300 kHz Medium frequency (MF): 300-3000 kHz High frequency (HF): 3-30 MHz Very high frequency (VHF): 30-300 MHz Ultra high frequency (UHF): 300-3000 MHz Super high frequency (SHF): 3-30 GHz Extremely high frequency (EHF): 30-300 GHz Note: above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that the atmosphere is effectively opaque to higher frequencies of electromagnetic radiation, until the atmosphere becomes transparent again in the so-called infrared and optical window freqency ranges. Analog.
Orthogonal frequency division modulation - Orthogonal frequency division modulation Orthogonal frequency division modulation (OFDM) is a modulation technique for modulating (encoding) digital information into an analog carrier signal. OFDM is sometimes called Discrete multitone modulation (DMT) An OFDM signal may be regarded as the sum of a number of individual sub-carrier signals, each modulated (typically using QAM) by its own modulating signal. This composite signal is then used to modulate the main carrier. OFDM is used in ADSL connections that follow the G.DMT (ITU G.922.1) standard. (Annex A refers to ADSL-over-POTS). The benefits of using OFDM are that it is easy to filter out noise (if a particular range of frequencies suffers from interference, the carriers within that range can be disabled or made to run slower), and that the upstream and.
Kohen - the Temple 3 Women and the priesthood 4 Post-Temple Theology and Practice 5 Marriages involving Kohanim 6 Conservative Jewish views 6.1 Reform Jewish views 7 Historical views 8 Recent Findings 9 The High Priest; Kohen Gadol 9.2 Powers 9.3 Restrictions 10 External Links The priesthood in the Bible The Torah appoints Aaron, brother of Moses, and Aaron's descendants as Kohanim (Numbers 3:1-4). They were given duties associated with the Tabernacle (Numbers 1:47-54; 3:5-13,44-51; 8:5-26). Since Aaron was a Levite, this means that all Kohanim are Levites. Most of the service in the Temple could be conducted only by Kohanim. Non-Kohen Levites assisted in the services of the Temple. After the destruction of the Second Temple in Jerusalem the formal role of priests in sacrifical services came to an end. This change.
Jamming - Radio Jamming Communications jamming is usually aimed at radio signals to disrupt control of a battle. A transmitter, tuned to the same frequency as the opponents receiving equipment and with the same type of modulation, can with enough power override any signal at the receiver. The most common types of this form of signal jamming are: Random Noise; Random Pulse; Stepped Tones; Wobbler; Random Keyed Modulated CW; Tone; Rotary; Pulse; Spark; Recorded Sounds; Gulls; and Sweep-through. All of these can be divided into two groups - obvious and subtle. Obvious jamming is easy to detect as it can be heard on the receiving equipment, it is some type of noise such as stepped tones (bagpipes), random-keyed code, pulses, erratically warbling tones, and recorded sounds. The purpose of this type of jamming.
Joseph Stefan - thermodynamic by his student Ludwig Boltzmann and hence known as the Stefan-Boltzmann law. Boltzmann treated a heat engine with the light as a working matter. This law is the only physical law of the nature named after one Slovene physicist. Today we derive the law from the Planck's Law of Radiation: and is valid only for ideal black objects. With his law Stefan determined the temperature of the Sun's surface and he got a value of 5430 °C. This was the first sensible value for the temperature of the Sun. Stefan provided the first measurements of the thermal conductivity of gases, treated evaporation and among others studied diffusion, heat conduction in fluids. For his treatise on optics he received the Richard Lieben award from the University of Vienna. Based on his.
John Cage - his old teacher Henry Cowell who also treated the piano in a non-standard way, asking performers to strum the strings with their fingers, for example. The Sonatas and Interludes of 1946-48 are widely seen as his greatest work for prepared piano. Pierre Boulez was amongst its admirers, and organised the European premiere of the work. The two composers struck up a correspondence, but this stopped when they came to a disagreement over Cage's use of chance in his music. It was also at Cornish that Cage founded a percussion orchestra for which he wrote his First Construction (In Metal) in 1939, a piece which uses metal percussion instruments to make a loud and rhythmic music. He also wrote the Imaginary Landscape No. 1 in that year, which uses record players as.
JPEG - pixel (eight each of red, green, and blue). This particular option is a lossy data compression method. First the image is converted from RGB into a different color space called YUV. This is similar to the color space used by NTSC and PAL color television transmission. The Y component represents brightness of a pixel, and the U and V components together represent the hue and saturation. This part is useful because the human eye can see more detail in the Y component than in the others. This enables the next step which is to reduce the U and V components to half size in both vertical and horizontal directions (called "downsampling" or "chroma subsampling"), thereby reducing the size in bytes of the whole image by a factor of two. For the.
JPEG 2000 - allow use of their intellectual property in connection with the standard without payment of license fees or royalties. Technical Discussion The aim of JPEG2000 is not only improved compression performance over JPEG but also adding (or improving) features such as scalability and editability to the JPEG2000 format. Moreover, very low and very high compression rates should be supported well, which includes lossless compression. JPEG2000 (as JPEG) applies a form of transform coding to compress images using the wavelet transform (as opposed to JPEG which uses DCT). Initially, images have to be transformed (from the RGB color space) to the well known YCrCb color space or to the RCT space (reversible component transform) leading to three components. The chrominance components can be but do not have to be down-scaled. After that, the.
Jupiter Ace - with 3K of RAM, expandable to 49K. While it had only one video mode, which displayed 24 rows of 32 columns of characters in black and white, it was possible to display graphics, by redefining the 8x8 pixel bitmap of any of the 128 characters. Like the ZX Spectrum, the machine's sound capabilities were restricted to beeps of programmable frequency and duration. The major difference from the ZX81, however, was that its designers intended it to be a machine for programmers: the machine came with Forth as its default programming language. Though this gave a great speed advantage over the interpreted BASIC that was used on other machines, it kept the ACE in a niche market. Sales of the machine were never very large; surviving machines are now (October 2001) quite.
IEEE 802.11 - 50 metres with the low-gain omnidirectional antennas typically used in 802.11b devices. 802.11b has a maximum throughput of 11 Mbit/s, however a significant percentage of this bandwidth is used for communications overhead; in practice the maximum throughput is about 5.5 Mbit/s. Metal, water, and particularly thick walls absorb 802.11b signals and decrease the range drastically. 802.11 runs in the 2.4 GHz spectrum and uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) as its media access method. With high-gain external antennas, the protocol can also be used in fixed point-to-point scenarios (8 kilometres), reports of up to 80-120 km line of sight) to replace costly leased lines, or in place of very cumbersome microwave communications gear. Current cards can operate at 11 Mbit/s, but will scale back to 5.5, then 2,.
Impedance match - Impedance match Electricity It is usually very important to transfer power from one stage of an electronic device to the next. To transfer the maximum amount of power, the output impedance of one stage must be the same as the input impedance of the next stage. Impedance is the resistance of a circuit to alternating current. If a small impedance is connected to a big impedance, then the power that can pass through the connection is limited by the larger impedance. To solve this problem, engineers use combinations of transformers, resistors, inductors and capacitors. Impedances matched by transformers are used for high power circuits. A transformer converts alternating current at one voltage to another voltage, however the power remains the same, except for conversion losses. The side with the lower.
Imperial Stormtrooper - the Galactic Empire feels may threathen their order, security or integrity. They are very highly disciplined, and answer only to those of the Emperor. They do not fear death, and will carry out any order given without hesitation or concern for their own security whatsoever. They are the kamikaze soldiers of the Galactic Empire. Stormtroopers are truly independent of the Imperial Navy or the Imperial Army chains of command, as they have their own command structure, ranking system and support facilities. However, if such a situation occurs, a Company Commander can give command to any regular officer over any given squad or platoon. Stormtroopers, as depicted in the Star Wars films, are notoriously poor marksmen. Their organization manners are similar to those of the Imperial Army. In the Stormtroops, the primary.
International Atomic Time - International (TAI) or International Atomic Time is a very accurate and stable time scale. It is an average of the time kept by many cesium clocks (atomic clocks) all over the world, and has been available since 1955. True high-precision TAI times can only be determined after the fact, as atomic time is determined by the reconciliation of the observed differences between an ensemble of atomic clocks maintained by a number of national time bureaux. This is done under the auspices of the International Bureau of Weights and Measures. However, atomic clocks are so accurate that only the most precise time computations need to use these corrections, and most time service users use atomic clocks that have been previously referenced to TAI to estimate TAI times for most purposes. Coordinated Universal.
Industrial and manufacturing engineering - and design costs, it is frequently "factored" into subassemblies that are designed and developed once and reused in many slightly different products. For example, a typical tape-player has a precision injection-molded tape-deck produced, assembled and tested by a small factory, and sold to numerous larger companies as a subassembly. The tooling and design expense for the tape deck is shared over many products that can look quite different. All that the other products need to have are the necessary mounting boles and electrical interface. Quality control It's a truism that "quality is free." Very often, it costs no more to produce a product that always works, every time it comes off the assembly line. It requires a conscious effort during engineering, but it reduces the cost of waste and rework quite.
Inductor - not offer any resistance to direct current (an actual one does slightly), except when the current is switched on and off, then it makes the change more gradual. When a sinusoidal alternating current flows through an inductor, a sinusoidal alternating voltage (or electromotive force, abbr. emf) is induced. The amplitude of the emf is related to the amplitude of the current and to the frequency of the sinusoid by the following equation. V = I × Ï‰L where ω is the angular frequency of the sinusoid defined in terms of the frequency f as ω = 2Ï€f The term ωL is known as inductive reactance, which is denoted by the symbol XL and is the positive imaginary component of impedance. Table of contents showTocToggle("show","hide") 1 Construction 2 History 3 See also.
