08-16-2017, 08:46 PM
This article is presented by:Germano Gon alves Capela, Nuno Pessanha Santos, Jo o Marques Vieira, C sar Bastos Monsanto
Escola Naval
Departamento de Armas e Electr nica
INTRODUCTION
The genesis of this work is the interest of the Portuguese Navy in measuring physical parameters over long distances, as the result of an impact of a missile in a naval platform. The analysis of those parameters may provide information about the effects of the impact on the platform and on personnel .First of all, the data collection should be made , and then this data should be transmitted in are liable manner over a long distance (not less than 3Nautical Miles for safety reasons).The main requirements for the system were low cost and the use of off-the-shelf technology ,being aware that this factor would influence the first . The specificity of the measurements was determinant in the project phase: the impact of a missile has hi-speed effects, which need high sampling rates. At the same time, this would produce an undesirably high amount of data that may make the transmission (there are limitations in the available bandwidth), recording and processing more difficult .A data logger was used with high sampling rate , which is connected to the analog sensors. The visual record of events was done using a camera(see Figure 1). Two Wi-Fi routers, each associated with a Radio-frequency (RF) amplifier were used ,together with high-gain omnidirectional antennas .Various experiences have been made with the Wi-Fi technology, namely on remote vehicle control (Hamilton and Hamilton 2007) and long range packet transmission (Flickenger, Okay et al.2008), showing that even with some constraints(Anastasi , Borgia et al. 2004; Anastasi, Conti et al.2004), it is viable its use in this case. In this paper we shall start by addressing the problem of avoiding the Fresnel Zone (Seybold2005) so as to use open space transmissions. Next we will discuss the choice of each equipment selected for the project. As a way to ensure that the builder s specifications were consistent, all the equipments were tested. The routers, amplifiers and antennas were tested with a well calibrated device (Spectrum Analyzer from GOAME1). In order to replicate reality, the whole system was tested in the estuary of the Rio Tejo (near Lisbon), achieving a maximum distance of approximately 4 nautical miles between end points. The results of these test sand their interpretation are presented.2. Specific problems a. The Fresnel Zone One of the issues to consider when implementing a telecommunication s system is the Fresnel Zone. In the Fresnel Zone, interferences resulting from multi-path phenomena (Seybold2005) can distort a signal considerably.
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