Emergency and operational low and medium frequency band radio communications system for underground mines

1991 ◽  
Vol 27 (4) ◽  
pp. 780-790 ◽  
Author(s):  
L.G. Stolarczyk
Keyword(s):  
Frequency Band ◽  
Underground Mines ◽  
Medium Frequency ◽  
Radio Communications ◽  
Communications System

scholarly journals An Improved Image Steganography Scheme Based on Partial Preservation Embedding Algorithm for Wireless Visual Sensor Networks

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Qian Shen ◽  
Tao Jiang ◽  
Yongjun Zhu ◽  
Yin Wu
Keyword(s):  
Sensor Networks ◽  
Frequency Band ◽  
Poor Performance ◽  
Least Significant Bit ◽  
Medium Frequency ◽  
Visual Sensor ◽  
Secret Data ◽  
Visual Sensor Networks ◽  
Noise Interference ◽  
Wireless Visual Sensor Networks

With the continuous improvement of encryption algorithms, some applications based on the architecture of wireless visual sensor networks have gradually shifted their attention to the imperceptibility and antijamming performance of secret images. To reduce the probability of secret images being detected, the current research focuses on hiding secret data in the least-significant bit of the cover image in the spatial domain or embedding data into the coefficients of the high-frequency band in the transformational domain, which usually leads to poor performance in a hostile environment. Therefore, some researchers proposed to substitute the coefficients of the medium-frequency band in the transformational domain with secret information to enhance the anti-interference performance. However, this idea would severely affect the imperceptibility of secret images. As a result, an improved version based on the partial preservation embedding algorithm was designed in this paper. Theory analysis and simulation results indicate that the proposed scheme performs better than the existing methods by directly substituting the coefficients of the medium-frequency band in the transformational domain, especially in the case of strong noise interference.

Marine Position Fixing Systems in Use Today

1950 ◽  
Vol 3 (4) ◽  
pp. 319-331
Author(s):  
H. E. Hogben
Keyword(s):  
Frequency Band ◽  
Direction Finding ◽  
Radio Spectrum ◽  
Medium Frequency ◽  
Marine Traffic ◽  
Wide Range ◽  
Navigational Aids ◽  
Potential Use ◽  
New Facilities

Before the war the only radio navigational aids in current use by shipping were direction finding systems, operating in the medium frequency band of the radio spectrum.During the war, not only were many new types of position fixing systems evolved, but radar techniques were also developed, thus making available a wide range of new facilities of potential use both to ships of many different categories and to port and harbour authorities for the supervision of marine traffic.

scholarly journals Underground Radio Propagation on Frequency Band 97 Mhz – 130 Mhz

2018 ◽  
Vol 7 (3.2) ◽  
pp. 722 ◽  
Author(s):  
S Suherman ◽  
Ali Hanafiah Rambe ◽  
Agustiar Widodo Tanjung
Keyword(s):  
Frequency Band ◽  
Radio Propagation ◽  
Future Application ◽  
Propagation Characteristics ◽  
Radio Communications ◽  
Earthquake Detection ◽  
Measurement Results ◽  
Link Budget ◽  
Underground Radio ◽  
Propagation Measurement

Radio communications do not work only in the air and underwater, but also underground. Some applications such as mining and earthquake detection require underground radio devices. This paper reports an assessment of underground radio characteristics for frequency band 97 MHz to 130 MHz. The assessments were performed through an experimental propagation measurement and a mathematical prediction. Both assessments then are compared by using the normalized graph to predict propagation characteristics so that correct link budget for future application can be assisted. The mathematic analysis and measurement results still produce huge errors; achieving 50.33% for frequency 130.762 MHz, 17.58% for 109.818 MHz and 13.38% for 97.335 MHz. Error can be minimized when the ground permittivity is more precise  

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