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Victor Rocha





Updated: 2014-10-04T21:22:05.527-07:00

 



Texto PDS

2008-04-30T16:19:48.058-07:00

1Fifty years ago the publications of Claude E, Shannon brought the sampling theorem to the broad attention oi communication engineers. This article demonstrates how practicians, theoreticians, and mathematicians discovered the implications of the sampling theorem almost independent of one another.In 1948 and 1949, Claude E. Shannon published the two revolutionary papers in which he founded the information theory [1, 2]. In [1] the sampling theorem is formulated as “Theorem 13”:Lei f(t) contam no frequencies over W. ThenIt was not until these papers were published that the theorem known as “Shannon’s sampling theorem” became common propriety among communication engineers, although Shannon himself writes in [2] thatThis is a fact which is common knowledge in the communication art.A few times further on, however, he adds:But in spire of its evident importance [it] seems not to have appeared explicitly in the literature of communication theory.The following analysis takes the above statement as its starting point. It will become apparent that mathematicians, practicians, and theoreticians in communication engineering carne across the implications of the sampling theorem almost independent of one another, and that the Links between them did not emerge until later stages of this development.THE PRACTICIANSIn communication engineering, the first experiments with time-division multiplexing (TDM) in telephony led to the questions of how and how often it is necessary lo sample a continuous-time signal.The attempt to transmit more than one signal simultaneously over a single wire began shortly after the early commercial successes with telegraphy in the 1840s. The first proposals for TDM using synchronously rotating commutators derive from F. C. Bakewell (1848), A. V. Newton (1851). and M. B. Farmer (1853). Technically more accomplished methods were then developed by B. Meyer (1870), J. M. E. Baudot (to 1874), as well as P. Lacour and P. B. Delany (1878) [ 4]. It is significant not only that methods were used in which complete telegraphic signals from different transmitters were placed in chronological order (e.g., Baudot), but that certain systems were also equipped with fast rotating commutators which were able to transmit at least two samples of each elementary signal (egg., Delany). This technique makes additional synchronization between transmitterand sampler unnecessary. One of these fast rotating commutators, the “distributor” of the telegraphy system by F. J. Patten (around 1891), was used for the first demonstration of TDM of telephone signals. The inventor’s name was Willard M. Miner. He had his method patented in 1903 following many years of preliminary experiments [5]. Figures 1 and 2 from [6] show the circuit diagram and the “Patten Distributor” which was used. Miner determined the required sampling rate experimentally [6]:It will be understood, then, that the apparatus devised by Mr. Miner, while in its general form the same as that heretofore used for multiplex telegraphy — or telephony for that matter — such apparatus is run at a much greater speed so as to bring the frequency of the closures of connection upon the several! Branches or sub-circuits up lo a rate approximating in greater or less degree the rate of the vibrations of the overtones characterizing speech. A rate of closure of 1,000 or 2,000 per second will nor answer the purpose, but as the rate increase and passes beyond 3,000, improved results become apparent, and are marked-ly better when a rate of 3,500 or 3,600 per second is reached; the best results being obtained with a rate of about 4,300 per second.Miner thus assumed that the sampling rate would coincide approximately with the upper frequency components of speech. In actuality, his telephone apparatus will have had a cutoff frequency of barely more than 2 kHz, which fulfills the requirements of the sampling theorem.Since a theoretical clarification of the sampling process was not forthcoming, pronouncements concerning the sampling rate in publications as well as patent appl[...]



Segurança (Bluetooth)

2007-08-27T11:16:42.343-07:00

Link



Tudo sobre RFID!!!!

2007-07-24T11:42:34.836-07:00

Aqui









Blogs sobre eletrônica

2007-07-06T16:10:46.853-07:00

Programador de Pic's



Link


Peter's electronic


Link



Up p/ o blog...

2007-07-18T12:16:34.468-07:00

Site de vendas bastante completo inclusive com transceivers:

Symphony

Site de um excelente distribuidor de componentes para eletronica e microeletrônica:

Farnell

Um dos maiores destribuidores de componentes eletrônicos da America Latina:

Trancham

Site com kit's de desenvolvimento, e placas microprocessadas:

Kit-MCU






Multi-channel Transceiver ICs Atmel

2007-07-03T11:45:34.474-07:00

ATA5423/ATA5425/ATA5428/ATA5429
(100 pages, revision C, updated 05/06)
The ATA5423 is a highly integrated 315/345/433/868/915 MHz ASK/FSK multi-channel half-duplex transceiver with very low power consumption supplied in a small 7 x 7 mm QFN48. package. The receive part is built as a fully integrated low-IF receiver. It integrates a fractional-N synthesizer with a direct PLL modulation scheme for FSK transmission and a switching of the PA for ASK transmission.

Datasheet

ATR2406
(25 pages, revision M, updated 02/07)
The ATR2406 is a single chip RF-transceiver intended for applications in the 2.4 GHz ISM band. The QFN32 packaged IC is a complete transceiver including image rejection mixer, low IF filter, FM demodulator, RSSI, TX preamplifier, power-ramping generator for external power amplifier, integrated synthesizer, and a fully integrated VCO and TX filter. No mechanical adjustment is necessary in production. The RF-transceiver offers a clock recovery function on-chip.

Datasheet

T2803

(28 pages, revision I, updated 07/05)
2.4 GHz WDECT/ISM Single-chip Transceiver.


Datasheet

(image)






Stand-alone RF receivers Microchip

2007-07-03T11:09:34.498-07:00

Receptores de rf independentes, ele suportam modulações ASK,FSK,FM e posuem o emvolucro 32/TQFP.

Datasheets:

Modelos rfRXD0420/0920








OFF-Tópic

2007-06-26T13:20:36.316-07:00

Link muito bacana de um eng. q fez todas os experimentos das revistas.

Link



Módulos de RF On-Shine

2007-06-26T12:43:20.448-07:00

Módulos de RF marca On-Shine na freqüência 433MHz.

Link



Módulos de RX, TX Linx

2007-06-26T12:42:02.924-07:00

Módulos de 433MHz e 315MHz, com chip Linx com o alcance de 150 metros, de fácil uso.

Link

Obs: Os equipamentos estão no meio do site, vc tb pode encontrar o datasheet do equipamento no mesmo link!



Módulos de Transmição Telecontrolli

2007-06-26T12:22:48.502-07:00

Soluções prontas de transmissores e receptores, em 315Mhz ou 433,92Mhz

Link



SIMBOLOS DAS CLASSES DE EMISSÃO

2007-06-26T12:05:52.019-07:00

Esse link comenta sobre os simbolos das classes de emissão.

Link






Projetos estudantis facilitam a vida de deficientes

2007-06-18T12:01:28.763-07:00

Para + informações, click aqui!!!