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 Download Full ArticleOrbiting Satellite Carrying Amateur Radio
Amateur Radio Operators (Hams) who share an active interest in building, launching and then communicating with each other through non-commercial Amateur Radio satellites. By any measure, AMSAT’s.Amatuer Radio Satellite Group) track record has been impressive. Since its founding 25 years ago, AMSAT has used predominantly volunteer labor and donated resources to design, construct, and, with the added assistance of international government and commercial agencies, successfully launch, over 30 Amateur Radio satellites into Earth orbit. Today, almost 20 of these satellites are operational. These satellites were generally called as OSCAR (Orbiting Satellite Carrying Amateur Radio).This paper focus on various technical aspects of OSCAR from its history, tracking, accessing up to its technology.

The Space age is barely a half century old .During this time a considerable amount of money is spent on space exploration and the related technologies .The investment has clearly begun pay of-earth satellites are the prime example . For nearly a decade most international telecommunications have been handled by satellite.

Orbiting Satellites Carrying Amateur Radio (OSCAR) series of small satellites was initiated for radio amateurs to experience satellite tracking and participate in radio propagation experiments. The World Administrative Radio Conference (WARC) allocated frequencies for the Amateur Satellite Service Transmitting low-powered signals, initially battery operated and offering short lives, the satellites have become increasingly sophisticated. More recently, they have served school science groups, provided emergency communications for disaster relief, acted as technology demonstrators, and transmitted Earth imagery.

The resourcefulness, ingenuity and skill of the Amateur Radio satellite community in the years have made a fascinating story. Hams have pursued the dream of reliable, predictable, long-distance and long-duration radio communication on different frequencies – from hf to microwaves. Each successive OSCAR has been one more step toward the realization of that dream. This paper covers the basic facts of OSCAR, its tracking, accessing and so on……..

The Space Age, was marked from the launch of Sputnik-I on October 4, 1957. OSCAR-I WAS launched on December 12, 1961.OSCAR –III, the first amateur satellite with a “transponder” was launched on March 9, 1965. In almost 40 years since the launch of first amateur satellite, the related technology has seen great advances, contributing to the exponential growth in the popularity of OSCAR operation.

Download Full ArticleOrbiting Satellite Carrying Amateur Radio

Download Full ArticleDigital Watermarking Using Wavelet Transforms

                With the rapid growth of Internet and networks technique, multimedia data transforming and sharing is common to many people. Multimedia data is easily copied and modified, so necessity for copyright protection is increasing. It is the imperceptible marking of multimedia data to “brand” ownership. Digital watermarking has been proposed as technique for copyright protection of multimedia data. Digital watermarking invisibly embeds copyright information into multimedia data. Thus, digital watermarking has been used for copyright protection, finger printing, copy protection and broadcast monitoring. Indeed, a watermarking algorithm requires both invisibility and robustness, which exist in a trade-off relation. Thus good watermarking algorithm must be satisfied the requirements.

                 The process of digital watermarking involves the modification of the original multimedia data to embed a watermark containing key information such as authentication or copyright codes. The embedding method must leave the original data perceptually un-changed, yet should impose modifications which can be detected by using an appropriate extraction algorithm. Common types of signals to watermark are images, music clips and digital video.  The application of digital watermarking to still images is concentrated here. The major technical challenge is to design a highly robust digital watermarking technique, which discourages copyright infringement by making the process of watermarking removal tedious and costly.

1.1 Advantage of frequency domain watermarking

                  In general, the digital watermarking is classified into two classes by depending on the domain of watermarking embedding: the spatial domain watermarking and the frequency domain watermarking. The spatial domain watermarking algorithms usually embed the watermark to the least significant bits (lsbs) of the image pixels. The watermark is embedded on randomly selected pixels using neighbours dependant function. In the detection process, the idea is to verify the surrounding pixels to decide if one has truly been modified. The detection of changes in small details of the image is based on mathematical morphology. Furthermore, it is able to reject small distortion introduced by high quality image compression. However, the technique suffers from the major drawback of spatial domain watermarking: frequency localization of modifications is difficult. Because the marks are on certain particular pixels, it is often impossible to detect frequency alterations applied to the entire image. .

Download Full ArticleDigital Watermarking Using Wavelet Transforms