• Publications of The Korean Astronomical Society
• /
• v.15 no.spc2
• /
• pp.21-25
• /
• 2000

The ionosphere, the atmosphere of the earth ionized by solar radiations, has been strongly varied with solar activity. The ionosphere varies with the solar cycle, the seasons, the latitudes and during any given day. Radio wave propagation through or in the ionosphere is affected by ionospheric condition so that one needs to consider its effects on operating communication systems normally. For examples, sporadic E may form at any time. It occurs at altitudes between 90 to 140 km (in the E region), and may be spread over a large area or be confined to a small region. Sometimes the sporadic E layer works as a mirror so that the communication signal does not reach the receiver. And radiation from the Sun during large solar flares causes increased ionization in the D region which results in greater absorption of HF radio waves. This phenomenon is called short wave fade-outs. If the flare is large enough, the whole of the HF spectrum can be rendered unusable for a period of time. Due to events on the Sun, sometimes the Earth's magnetic field becomes disturbed. The geomagnetic field and the ionosphere are linked in complex ways and a disturbance in the geomagnetic field can often cause a disturbance in the F region of the ionosphere. An enhancement will not usually concern the HF communicator, but the depression may cause frequencies normally used for communication to be too high with the result that the wave penetrates the ionosphere. Ionospheric storms can occur throughout the solar cycle and are related to coronal mass ejections (CMEs) and coronal holes on the Sun. Except the above mentioned phenomena, there are a lot of things to affect the radio communication. Nowadays, radio technique for probing the terrestrial ionosphere has a tendency to use satellite system such as GPS. To get more accurate information about the variation of the ionospheric electron density, a TEC measurement system is necessary so RRL will operate the system in the near future.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.26 no.9
• /
• pp.821-827
• /
• 2015

Electromagnetic waves which are emitted from the Sun due to solar flare explosion can cause failures in HF radio communications in the day-side area of the Earth, that is so-call as Radio Blackouts. The international scale representing the severity of the Radio Blackouts is determined by the solar X-ray flux which is measured by United States Geostationary Operational Environmental Satellite. However, the scale is not always applicable to HF communication users in the different area on the Earth, because the HF communication effects depend not only on the X-ray strength but also on the subsolar point location. To solve this problem, we developed a HF radio spectrum monitoring system utilizing a spectrum analyzer. This system conducts a real-time measure of the HF spectrum, and automatically calculates signal to noise ratios and the occurrences of the HF blackouts as comparing with the interference level which is described from the ITU recommendation.

• Ocean and Polar Research
• /
• v.38 no.4
• /
• pp.325-330
• /
• 2016

Partial high frequency bands were allocated to the operation of ocean surface radars that monitor the sea surface currents and waves in WRC-12. On that basis, government-related organizations revised the table of domestic frequency allocation. In order to study radio environments in the allocated bands for ocean radar, tests of the radio signal spectrum were carried at 7-sites using the receiver of the ocean surface radar system operated with a shutdown of the transmitter for 10-60 min. The results showed that no serious radio noises occur at 25 and 43 MHz bands, indicating a good radio environment for the ocean surface radar operation. However, at 13 MHz band, it was difficult to generate stable and confidential data from the ocean surface radar because serious radio noises occurred continuously.

• Ocean and Polar Research
• /
• v.44 no.4
• /
• pp.287-296
• /
• 2022

High-frequency (HF) radar measures sea surface currents from the radio waves transmitted and received by antenna on land. Since the data quality of HF radar measurements sensitively depend on the radio wave environment around antenna, Antenna Pattern Measurements (APM) plays an important role in evaluating the accuracy of measured surface currents. In this study, APM was performed by selecting the times when the background noise level around antenna was high and low, and radial data were generated by applying the ideal pattern and measured pattern. The measured antenna pattern for each case was verified with the current velocity data collected by drifters. The radial velocity to which the ideal pattern was applied was not affected by the background noise level around antenna. However, the radial velocity obtained with APM in the period of high background noise was significantly lower in quality than the radial velocity in a low noise environment. It is recomended that APM be carried out in consideration of the radio wave environment around antenna, and that the applied result be compared and verified with the current velocity measurements by drifters. If it is difficult to re-measure APM, we suggest using radial velocity in generating total vector with the ideal pattern through comparative verification, rather than poorly measured patterns, for better data quality.

• Ocean and Polar Research
• /
• v.34 no.4
• /
• pp.453-462
• /
• 2012

Ocean surface current data in Korea was collected using sets of High-Frequency Ocean Surface Radars (HFOSRs) with 25 radial sites in the frequency range of 5~43 MHz. Site selection and the correct installation of HFOSR are very important considerations in order to secure continuous and reliable results. The installation procedures of HFOSR are summarized as follows: 1. Survey area selection; 2. Investigation of ambient radio waves and installation environment; 3. Domestic license of radio station; 4. Installation of antenna and housing of electrical and communication devices. The current work describes the entire processes of HFOSR installation within Korea.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.10 no.2
• /
• pp.250-256
• /
• 2006

The revision of radio waves act, which took effect on July 1,2005, widened the bandwidth of PLC from $9kHz{\sim}450kHz$ to $9kHz{\sim}30MHz$. This high upper limit of frequency may cause the interference in HF wireless communications. From this point of view, the goal of this research is to suggest the estimation method of whether-or-not the interference occurs and furthermore offer countermeasures to avoid it hereafter. Ministry of Information and Communication Radio Research Laboratory(MIC-RRL)has been researching for the interference and devoting themselves to turn out how much it affects to HF wireless communications since the revision took effect. This research suggests some estimation methods with receivers, signal generators, or SINAD(Signal to Noise and Distortion) Meter which is so suitable for the RF environment that we can overcome the existing limit to the EMC environment. In addition, this research is focused on securing the environment for wireless communications by establishing the safety zone or suggesting the ways to prohibit the use of the bandwidth, which may cause serious interference, in order to minimize the effect of PLC on HF maritime mobile telecommunications.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.2 no.1
• /
• pp.20-28
• /
• 1977

The shipping business which consistutes main stream of foreign trades in the world desires more larger and higher speed ships to convey a large amount of cargo at a time rapidly and safely. They also want to introduce new techniques into transportation system so to meet the rapid growing demand of maritime mobile communications with the improvement of efficiency of radio apparatus and reduction of the hard labors of radio operators mechanization and modernization of radio apparatus is necessary. Now HF band is used mainly for communications between maritime mobile stations and coast stations but the quality of received signal is not so good and the coverage is not sufficient by the condition of propagation of waves. There is also limitation of channel capacity in HF band. So to cope with or improve of these defects and meet the demands of modern maritime communication it is essential to introduce maritime satellite communication system in this field. By using the maritime satellite we can establish high quality communication circuits as maritime Telex, Faximile, high speed data transmission line and can expand coverages. Therefore industrial rationalization of marine transportation is possible with the reduction of painful labors of radio operators by improving safety and promoting of efficiency of movement of ships and freights. Obviously it is prospected that the introduction of maritime satellite communication system will bring a rapid promotion of its usuage in maritime mobile communication field and also anticipated that maritime satellite communication system will be a main current in maritime mobile communication field over the world in the near future with moderated cost of transmission links as in the case of INTELSAT in the past 10 years after its first launching.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.35 no.6
• /
• pp.109-120
• /
• 2023

The High-Frequency Radar (HFR) is an equipment designed to measure real-time surface ocean currents in broad maritime areas.It emits radio waves at a specific frequency (HF) towards the sea surface and analyzes the backscattered waves to measure surface current vectors (Crombie, 1955; Barrick, 1972).The Seasonde HF Radar from Codar, utilized in this study, determines the speed and location of radial currents by analyzing the Bragg peak intensity of transmitted and received waves from an omnidirectional antenna and employing the Multiple Signal Classification (MUSIC) algorithm. The generated currents are initially considered ideal patterns without taking into account the characteristics of the observed electromagnetic wave propagation environment. To correct this, Antenna Pattern Measurement (APM) is performed, measuring the strength of signals at various positions received by the antenna and calculating the corrected measured vector to radial currents.The APM principle involves modifying the position and phase information of the currents based on the measured signal strength at each location. Typically, experiments are conducted by installing an antenna on a ship (Kim et al., 2022). However, using a ship introduces various environmental constraints, such as weather conditions and maritime situations. To reduce dependence on maritime conditions and enhance economic efficiency, this study explores the possibility of using unmanned aerial vehicles (drones) for APM. The research conducted APM experiments using a high-frequency radar installed at Dangsa Lighthouse in Dangsa-ri, Wando County, Jeollanam-do. The study compared and analyzed the results of APM experiments using ships and drones, utilizing the calculated radial currents and surface current fields obtained from each experiment.