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.
Read the rest of this article:
<http://en.wikipedia.org/wiki/Distributed_element_filter>
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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>
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Wiktionary's word of the day:
selenology (n):
The scientific study of the Moon
<http://en.wiktionary.org/wiki/selenology>
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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>