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 compared to VHF frequencies. The frequencies of 300–3000 MHz are always at least an order of magnitude above the MUF (Maximum Usable Frequency). The MUF for most of the earth is generally between 25–35 MHz. Higher frequencies also benefit less from ground mode transmission. However, the short wavelengths of UHF frequencies allow compact receiving antennas with narrow elements; many people consider them less ugly than VHF-receiving models
On December 29, 1949 KC2XAK of Bridgeport, Connecticut became the first UHF television station to operate on a regular daily schedule.
In the United States, UHF stations (broadcast channels above 13) originally gained a reputation for being more locally owned, less polished, less professional, less popular, and for having a weaker signal than their VHF counterparts (channels 2–13). The movie UHF, starring Weird Al Yankovic, parodied this phenomenon.
However, with the emergence of additional broadcast television networks ( Fox, UPN, WB, and PaxThe PAX Network PAX TV PaxNet or simply PAX is a cable television network formed in 1998. PAX, which is owned by Paxson Communications, shows family-oriented programming. Its programming contains little or no sex, violence or strong language. Unlike most), the concentration of media ownershipConcentration of media ownership is a commonly used terms among media critics, policy makers, and others to characterize ownership structure of media industries. Media ownership is said to be concentrated usually in one or more of the following ways., and the proliferation of cable televisionCable television or Community Antenna Television CATV (and often shortened to 'cable') is a system of providing television, FM radio programming and other services to consumers through fixed coaxial cables, rather than by the older and more widespread rad, digital televisionDigital television DTV uses digital modulation and compression to broadcast video, audio and data signals to television sets.
Introduction A major use of DTV can be to carry more channels on the same amount of bandwidth. Another can be high-definition pro, and DSSDigital Satellite System (DSS) or Direct Broadcast Satellite (DBS is a technology to deliver a television or audio signal digitally, directly from an orbiting satellite to a consumer's one- to three-foot-diameter dish at the consumer's home or business. in the 1990sCenturies: 19th century 20th century 21st century Decades: 1940s 1950s 1960s 1970s 1980s 1990s 2000s 2010s 2020s 2030s 2040s Years: Events and trends Computers, technology Explosive growth of the Internet; decrease in the cost of computers and other techn, the distinction between UHF and VHF stations has virtually disappeared in the United States. Most HDTV stations (those using the ATSC television standard) broadcast their over-the-air signal in the UHF band.
In Britain, UHF television began with the launch of BBC2 in 1964, using a 625-line system (which had higher resolution, and therefore required greater bandwidth, than the existing 405-line system). BBC1 and ITV soon added their own 625-line services on UHF (British channels 21 to 69), and PAL colour was introduced on UHF only in 1967– 1969. VHF was phased out by 1986. Today all British terrestrial television channels (analog and digital) are on UHF. A drawback to this is the very large number of small relay transmitters needed to fill in gaps in the main transmitters' coverage, which would not have been necessary with a VHF system due to its different propagation characteristics.
LC circuit
An LC circuit is an electronic circuit made up of an inductor and a capacitor.
LC circuit's resonant frequency is equal to: formula_1
The angular frequency ω has units of radians per second.
LC circuits are used for creating signals at a particular frequency, or picking out a signal at a particular frequency from a more complex signal. An ideal LC circuit does not have resistance.
At LC circuit energy saves in the capacitor's electric field.
formula_2
U is energy and q is electric charge.
At LC circuit energy also save in the inductor's magnetic field.
formula_3
U is energy and i is electric current that flows in inductor.
Let's analyze an LC circuit's vibration. Vibrating LC circuit's total energy is U.
formula_4
Because circuit's resistance is 0, there is no energy that transmits to heat energy, and U is maintained regularity.
formula_5
So LC circuit's vibration is shown like that
formula_6
First consider the Electrical impedance of the series LC circuit. The total impedance is given by the sum of the inductive and capacitive impedances
formula_7
By writing the inductive impedance as formula_8 and capacitive impedance as formula_9
Resultingly the series connected circuit, when connected to a circuit in series, will act as a band-pass filter having zero impedance at the resonant frequency of the LC circuits.
The same analysis may be applied to the parallel LC circuit. The total impedance is then given by
formula_11
and after substitution of formula_12 and formula_13 we have
formula_14
which simplifies to
formula_15 .
Resultingly the parallel connected circuit will act as band-stop filter having infinite impedance at the resonant frequency of the LC circuit.
Application-specific integrated circuit
ASIC or Application-specific integrated circuit is a kind of integrated circuit. It is built for a particular use instead of for general-purpose use. Digital circuits are a common form of ASIC, but analog ASICs were manufactured beginning in the latter half of the 1990s.
ASIC has advantages compared to Programmable Logic Device or Standard Logic IC.
There are also disadvantages of ASIC.
Design of ASIC is gate array design, cell base design, embedded array design, standard cell design, and structured ASIC design.
Gate array design has elementary gate circuit at first base, (we) manufacture the products with putting ordered proper wire-layers.
Manufacturing is quick because a finished product needs only production of wire-layers and it is cheap because of mass production of its foundation.
However, because (we) form a circuit with formation of standard gate, it has worse contact rate and efficiency.
Cell base design uses wire-layer between block that was designed and arranged and logical circuit. and product is manufactured .
Performance is better than gate array, but time of making cell base is longer than time of making gate array, and cost of making cell base is more expensive than cost of making gate array.
Embedded array design Use finished functional block were located. It was rest of theory for wired to use part of gate array. It was called that gate array and basis of cell were compromising.
Standard cell design is a general term for gate array, cell base, embedded array. if standard cell is cell base IC, direction is different each company.
Structured ASIC design uses customization of standard subsystems to speed design and production.
Designers of ASIC use a hardware description language (HDL) such as Verilog or VHDL to describe the functionality of the design.
Photoelectric effect
The photoelectric effect is a phenomenon in physics. The effect is based on the idea that electromagnetic radiation is made of a series of particles called photons. When a photon hits an electron on a metal surface, the electron can be emitted. The emitted electrons are called photoelectrons. The effect is also called the Hertz Effect, because it was discovered by Heinrich Rudolf Hertz, but this name is not used often.
The photoelectric effect has helped physicists understand the quantum nature of light and electrons. The concept of wave–particle duality was developed because of the photoelectric effect. Albert Einstein proposed the Laws of Photoelectric Effect and won the Nobel Prize For Physics 1921.