A distributed element filter is an electronic filter in which capacitance, inductance and resistance are not localised in discrete capacitors, inductors and resistors as they would be in a conventional filter. Its purpose is to allow a range of signal frequencies to pass, but to block others. Conventional filters are constructed from inductors and capacitors, and the circuits so built are described by the lumped element model, which considers each element to be "lumped together" at one place. That model is conceptually simple, but it becomes increasingly unreliable as the frequency of the signal increases, or as the wavelength decreases. The distributed element model applies at all frequencies, and is used in transmission line theory; many distributed element components are made of short lengths of transmission line. There is no precise frequency above which distributed element filters must be used but they are especially associated with the microwave band. Distributed element filters are used in many of the same applications as lumped element filters, such as selectivity of a radio channel, bandlimiting of noise and multiplexing of many signals into one channel. The technology can be found in several mass-produced consumer items, such as the converters (figure 1 shows an example) used with satellite television dishes.

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_______________________________ Today's selected anniversaries:

1791:

French Revolution: Members of the National Guard fired into a large crowd that was gathered at the Champ de Mars in Paris to sign a petition demanding the removal of King Louis XVI. http://en.wikipedia.org/wiki/Champ_de_Mars_Massacre

1918:

Russian Revolution: Bolsheviks executed Tsar Nicholas II and his family at Yekaterinburg. http://en.wikipedia.org/wiki/Shooting_of_the_Romanov_family

1936:

Nationalist rebels attempted a coup d'état against the Second Spanish Republic, sparking the Spanish Civil War. http://en.wikipedia.org/wiki/Spanish_Civil_War

1955:

Disneyland in Anaheim, California, US, the only theme park to be designed and built under the direct supervision by Walt Disney, opened during a televised ceremony. http://en.wikipedia.org/wiki/Disneyland

2007:

TAM Airlines Flight 3054 crashed upon landing during rain at the Congonhas-São Paulo Airport in São Paulo, Brazil, killing 199 people, the highest death toll of any aviation accident in Latin America and the highest death toll of any accident involving an Airbus A320 airliner in the world. http://en.wikipedia.org/wiki/TAM_Airlines_Flight_3054

_____________________________ Wiktionary's word of the day:

selenology (n): The scientific study of the Moon http://en.wiktionary.org/wiki/selenology

___________________________ Wikiquote quote of the day:

They told us not to wish in the first place, not to aspire, not to try; to be quiet, to play nice, to shoot low and aspire not at all. They are always wrong. Follow your dreams. Make your wishes. Create the future. And above all, believe in yourself. --J. Michael Straczynski http://en.wikiquote.org/wiki/J._Michael_Straczynski