High frequency band communication application in Malaysia

High frequency (HF) radio frequencies are between 3 and 30 MHz.[1] Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters. Shortwave (2.310 - 25.820 MHz)[1] overlaps and is slightly lower than HF. Since the ionosphere often reflects HF radio waves quite well (a phenomenon known as skywave), this range is extensively used for medium and long range terrestrial radio communication. However, suitability of this portion of the spectrum for such communication varies greatly with a complex combination of factors[1]: • Sunlight/darkness at site of transmission and reception • Transmitter/receiver proximity to terminator • Season • Sunspot cycle • Solar activity • Polar aurora • Maximum usable frequency • Lowest usable high frequency • Frequency of operation within the HF rang

Gravitational Wave (GW) Classification, Space GW Detection Sensitivities and AMIGO (Astrodynamical Middle-frequency Interferometric GW Observatory)

After first reviewing the gravitational wave (GW) spectral classification. we discuss the sensitivities of GW detection in space aimed at low frequency band (100 nHz-100 mHz) and middle frequency band (100 mHz-10 Hz). The science goals are to detect GWs from (i) Supermassive Black Holes; (ii) Extreme-Mass-Ratio Black Hole Inspirals; (iii) Intermediate-Mass Black Holes; (iv) Galactic Compact Binaries; (v) Stellar-Size Black Hole Binaries; and (vi) Relic GW Background. The detector proposals have arm length ranging from 100 km to 1.35x109 km (9 AU) including (a) Solar orbiting detectors and (b) Earth orbiting detectors. We discuss especially the sensitivities in the frequency band 0.1-10 microHz and the middle frequency band (0.1 Hz-10 Hz). We propose and discuss AMIGO as an Astrodynamical Middle-frequency Interferometric GW Observatory.Comment: 10 pages, 2 figures, 1 table, Plenary talk given in Joint Meeting of 13th International Conference on Gravitation, Astrophysics, and Cosmology and 15th Italian-Korean Symposium on Relativistic Astrophysics, Ewha Womans University, Seoul, Korea, July 3-7, 201

Quantum engineering of squeezed states for quantum communication and metrology

We report the experimental realization of squeezed quantum states of light, tailored for new applications in quantum communication and metrology. Squeezed states in a broad Fourier frequency band down to 1 Hz has been observed for the first time. Nonclassical properties of light in such a low frequency band is required for high efficiency quantum information storage in electromagnetically induced transparency (EIT) media. The states observed also cover the frequency band of ultra-high precision laser interferometers for gravitational wave detection and can be used to reach the regime of quantum non-demolition interferometry. And furthermore, they cover the frequencies of motions of heavily macroscopic objects and might therefore support the attempts to observe entanglement in our macroscopic world.Comment: 12 pages, 3 figure

Passive intrusion detection system

An intrusion detection system is described in which crystal oscillators are used to provide a frequency which varies as a function of fluctuations of a particular environmental property of the atmosphere, e.g., humidity, in the protected volume. The system is based on the discovery that the frequency of an oscillator whose crystal is humidity sensitive, varies at a frequency or rate which is within a known frequency band, due to the entry of an intruder into the protected volume. The variable frequency is converted into a voltage which is then filtered by a filtering arrangement which permits only voltage variations at frequencies within the known frequency band to activate an alarm, while inhibiting the alarm activation when the voltage frequency is below or above the known frequency band

Gain Enhancement of a Wide Slot Antenna Using a Second-Order Bandpass Frequency Selective Surface

Gain enhancement of a wide slot antenna over a wide frequency band using a low profile, second order bandpass frequency selective surface (FSS) as a superstrate is presented in this paper. The proposed multilayered FSS with non-resonant unit cells in each layer allows in-phase transmission of waves radiated from the antenna over a 3dB bandwidth of about 50%. The design allows an enhancement of upto 4dBi in the antenna gain over the entire frequency band (5-8GHz) of operation. The FSS provides a very low insertion loss between the two transmission poles along with a linearly decreasing transmission phase over the band. The composite structure shows an impedance bandwidth (-10dB) of 65% with an average gain between 6-8dBi over the frequency band with a peak gain of 9dBi. Measurement results of the fabricated prototype matches well with the predicted values

Driven linear modes: Analytical solutions for finite discrete systems

We have obtained exact analytical expressions in closed form, for the linear modes excited in finite and discrete systems that are driven by a spatially homogeneous alternating field. Those modes are extended for frequencies within the linear frequency band while they are either end-localized or end-avoided for frequencies outside the linear frequency band. The analytical solutions are resonant at particular frequencies, which compose the frequency dispersion relation of the finite system.Comment: 4 pages, 3 figures, submitted to Phys. Rev.

Frequency‐Dependent Moment Tensors of Induced Microearthquakes

Analysis of 984 induced microearthquakes from The Geysers geothermal reservoir in California reveals that the retrieved moment tensors depend on the frequency band of the inverted waveforms. The observed dependence is more significant for the percentages of the double‐couple, compensated linear vector dipole, and isotropic (ISO) components than for the focal mechanisms. The average root‐mean‐square of the moment tensors obtained in different frequency bands is correlated with spectra of ambient noise. The percentages of double‐couple and ISO components tend to decrease and increase with the upper cutoff frequency (fu), respectively. This suggests that shear rupture radiates energy preferentially in a lower frequency band and tensile rupture in a higher frequency band. Events displaying a strong increase of the ISO with fu are confined within the same depth interval as the injection points. This might be related to the strong thermoelastic effects in the vicinity of injection points that promote opening of small cracks adjacent to the main fractures

Galactic Binary Gravitational Wave Noise within LISA Frequency Band

Gravitational wave noise associated with unresolved binary stars in the Galaxy is studied with the special aim of determining the upper frequency at which it stops to contribute at the rms noise level of the proposed space-born interferometer (LISA). The upper limit to this background is derived from the statistics of SN Ia explosions, part of which can be triggered by binary white dwarf coalescences. The upper limiting frequency at which binary stochastic noise crosses LISA rms sensitivity is found to lie within the range 0.03-0.07 Hz, depending on the galactic binary white dwarf coalescence rate. To be reliably detectable by LISA, the energy density of relic cosmological background per logarithmic frequency interval should be Omega_{GW}h_{100}^2>10^{-8} at f>0.03 Hz.Comment: 16 pages with 1 eps figure, aasms4.sty, to appear in the ApJ vol. 494 February 20, 1998 issu