Tour de transmission

Résumé

200px|thumb|Émetteur de Mayet (Sarthe), la cinquième plus haute construction de France Les tours de transmission ou émetteurs sont des structures destinées à émettre les ondes de la télévision et de la radio. Ce sont des constructions verticales (métalliques ou en béton) tripode de type autoportantes, néanmoins haubanées en raison des efforts de vent et dont l'emplacement a été particulièrement étudié. Ils sont généralement placés en rase-campagne, sur des points hauts ou au centre d'une vaste plaine pour bénéficier du meilleur dégagement. L'importance de la courbure terrestre et la géomorphologie locale a une influence décisive sur la portée d'un émetteur, dépendant aussi de la fréquence ou spectre de travail. Histoire Le a lieu la première transmission française de télévision, par René Barthélemy, présentée par Suzanne Bridoux devant 800 invités et avec une image de trente lignes (court métrage L'Espagnole à l'éventail, et prises de vues en direct), entre le laboratoire

Source officielle

https://fr.wikipedia.org/wiki/Tour_de_transmission

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A PROOF-OF-PRINCIPLE ECHO-ENABLED HARMONIC GENERATION EXPERIMENT AT SLAC

Pierre-Louis Pernet

In this paper we describe the technical design of an ongoing proof-of-principle echo-enabled harmonic generation (EEHG) experiment at the Next Linear Collider Test Accelerator (NLCTA) at SLAC.We present the design considerations and the technical details of the experiment.

2010

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This work was motivated by the increasing need for acoustic localization systems. The various localization systems that were implemented during this PhD include localization of snow avalanches, artillery and supersonic aircraft in the infrasound domain, the localization of helicopters, civilian aircraft, speakers and auditorium reflections in the audio domain and the localization of chirps in the underwater ultrasound domain. The "goniometer" is defined as an instrument that measures angles. An "acoustic goniometer" is therefore a system that measures the direction of arrival (DOA) of sounds, and thus estimates the source direction. A goniometer is made up of an antenna, composed of several sensors arranged in a particular geometry, and a calculation algorithm. The successive implementations were designed around a common framework, based on a two-step spatio-temporal process. The temporal step tackles the problem of the Time Delay Estimation along the antenna baselines, whereas the second step introduces the antenna geometry, in order to estimate the Direction of Arrival per se. The multi-sources case, as well as the outlier's rejection, is assured by a detection module, which uses the temporal and spatial properties of the propagation model. The performances of the TDE and the localization are studied as a function of every relevant parameter, in order to determine the optimal antenna to run the two-step process. The antenna design rules concern its geometry, its size and its orientation. The results presented in the applications chapter give a realistic idea of the goniometry capacities. Its performances are largely competitive to those of other techniques. Up to now, the goniometry developed during this work, fulfilled all prior requirements. Moreover, the goniometry appeared to be, in many cases, in advance with regards to technological tools such as the sound pick-up, the CPU implementation or installation constraints. The advice that could be given, when tackling a new antenna design, is firstly to visualize both spatial and temporal properties of the propagating waves and of the perturbating phenomena, and secondly to compare them to the goniometer characteristics. This work has demonstrated that the best performances were achieved for the goniometry of a unique stationary compact source generating broadband low pass signals in a homogenous medium without wind and noise, performed with a wide symmetrical broad-side antenna.

EPFL2002

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EPFL2002