• 한국통신학회논문지
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• 제33권8A호
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• pp.846-851
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• 2008

통신 산업의 급격한 발달로 통신서비스의 종류가 다양해지고 전파사용이 증가함에 따라 이전의 전파감시 시스템을 대체할 효율적이고, 지능화된 전파감시 시스템의 개발이 필요하게 되었다. 차세대 지능형 전파감시 시스템은 ITU-R, 무선설비규칙 및 전파법을 근간으로 하여 V/UHF대역의 On-Air 상의 아날로그 및 디지털신호에 대해 스펙트럼분석을 통한 채널전력과 주파수편차 및 편이, 점유대역폭(99% 또는 x-dB)을 정확하고 효율적으로 전파측정 할 수 있도록 개발되었다, 시스템의 주요 기능은 전파품질측정, 불요파(스퓨리어스, 고조파)측정, 고속스펙트럼측정, 주파수이용효율조사, 불법전파탐사, 운용감시이고, 본 논문에서는 차세대 지능형 전파감시 시스템의 주요기능 중 전파품질측정, 고속스펙트럼측정에 대해 기술한다.

• 천문학회보
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• 제39권2호
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• pp.60.1-60.1
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• 2014

In the center of an Active Galactic Nuclei(AGN) is a supermassive black hole which accretes matter from its surroundings. The radio-loud AGN launch two relativistic jets perpendicular to the accretion disk which terminates into radio lobes located up to megaparsec away. Blazars form a small subset of radio-loud AGNs with one of two relativistic jets pointing toward the observer's line of sight. Many blazars often show flares at different frequencies. And these flares at different frequencies are known that they often correlate with each other. In 2013 December, there was a gamma-ray flare in 3C 279, one of the brightest blazars, Dec 2013. So we want to reveal that whether this flare correlates with radio flare or not, and where the flare originate. With polarization observation at radio frequencies, we can study the physical properties of the magnetic field in the innermost regions of the relativistic jets. Therefore, we have conducted polarization monitoring of this source from Dec. 2013 to Jun. 2014 with KVN(Korea VLBI Network) radio telescopes at 22, 43 and 86GHz. Here we present the initial results of the monitoring of 3C 279. We prospect that we can reveal the origin of this gamma-ray flare by comparing with our radio data.

• Journal of information and communication convergence engineering
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• 제13권3호
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• pp.167-171
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• 2015

A radio over fiber (RoF) system is a kind of analog optical transmission system and considered as a strong candidate for the next-generation fronthaul link in the future mobile network. In RoF systems, nonlinearity compensation is essential to increase the link capacity. In this paper, we propose a nonlinearity detection and compensation scheme using a monitoring channel in RoF systems. A monitoring channel is added at the transmitter site and used for transmitting a reference signal in an RoF transmission. The nonlinearity in the RoF transmission is detected by comparing the received monitoring signal and the original reference signal at the receiver site. Finally, the nonlinearity is compensated at the receiver by giving the reverse function of the detected nonlinearity. Our results show that the proposed scheme can almost remove the error vector magnitude degradation induced by the nonlinearity in the RoF system.

• 천문학회보
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• 제25권1호
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• pp.49-49
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• 2000

• 비파괴검사학회지
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• 제30권3호
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• pp.244-256
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• 2010

Radio frequency identification(RFID) combined with wireless technology has good potential for structural health monitoring(SHM). We describe several advantages of RFID and wireless technologies for SHM, and review SHM examples with working principles, design and technical details for damage detection, heat exposure monitoring, force/strain sensing, and corrosion detection in concrete, steel, carbon fiber reinforced polymer(CFRP), and other materials. Various sensors combined with wireless communication are also discussed. These methodologies can be readily developed, implemented, and customized. There are some technical difficulties, but solutions are being addressed. Lastly, a surface acoustic wave-based RFID system is presented, and possible future trends of SHM based on RFID and wireless technology are presented.

• 과학교육연구지
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• 제34권2호
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• pp.432-439
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• 2010

이 연구의 목적은 전파가 전리층에서 반사되는 원리를 이해하고, 우주환경 변화가 전파 통신에 미치는 영향을 알아보는 것이다. 연구를 위하여 SID모니터를 설치하고, 안테나를 제작하였다. SID 모니터로 일본 Evino에서 송신하는 22.2kHz 전파를 수신하였다. 수신된 전파의 세기를 이용하여 전리층 D층의 상태를 분석하였다. 결과를 요약하면 다음과 같다. 저주파 통신은 규칙적인 일변화를 가지고 상태가 변하게 된다. D층의 생성, 소멸과 관련하여 저주파 통신은 일몰과 일출 직후 전파의 세기가 약해지는 현상이 나타난다. 태양의 남중고도에 따라 낮 시간 전파의 세기가 변하는 것을 관찰했다. 밤에는 D층이 사라져 매우 불규칙한 변화를 보인다. 전리층은 계절적인 변화를 비롯하여, 여러 요인에 의해 변하는 것으로 생각되며 보다 자세한 변화 과정을 이해하기 위해서는 긴 시간 동안의 전파 관측이 필요하다.

• 천문학회보
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• 제40권1호
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• pp.42.2-42.2
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• 2015

High frequency peakers (HFPs) are promising candidates for young active galactic nuclei (AGNs). Their small physical scale (< 1 kpc) and radio spectrum peaked at high frequency (> 5 GHz) are suggestive that it has been only about $10^2-10^3$ years since a central massive black hole in their host galaxies was launched. Until recently however, long-term monitoring radio observations at frequencies which are high enough to cover the true peak of HFP candidates were rare. Therefore, previous HFP samples are often contaminated by blazars, which are highly variable, hence may show a similar radio spectrum as HFPs depending on the observational epoch. In this work, we challenge to identify genuine young AGNs by monitoring HFP candidates at high radio frequencies. We performed single-dish monitoring of 19 candidates in 18 epochs over 2.5 years at 22 and 43 GHz using the Korean VLBI Network (KVN). Also, using KaVA, a combined array of the KVN and the VERA in Japan, we carried out 22 GHz VLBI observations of two HFPs and one blazar selected from our sample in order to compare their parsec scale (milli-arcsecond scale) morphology. HFPs are expected to have double/triple features, so called compact symmetric objects, which are scaled-down versions of extended radio galaxies, while blazars typically show core-jet morphology. We discuss the properties of AGNs at their very early evolutionary stage based on the results of the KVN and KaVA observations.

• 천문학회지
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• 제48권5호
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• pp.267-275
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• 2015

Simultaneous time monitoring observations of H₂O and SiO maser lines were performed toward the D-type symbiotic binary system V407 Cyg with the Korean VLBI Network single dish radio telescope. These monitoring observations were carried out from March 2, 2010 (optical phase ϕ = 0.0), 8 days before the nova outburst on March 10, 2010 to June 5, 2014 (ϕ = 2.13). Eight days before the nova outburst, we detected the SiO v = 1, 2, J = 1–0 maser lines which exhibited values of 0.51 K (∼ 6.70 Jy) and 0.71 K (∼ 9.30 Jy), respectively, while after the outburst we could not detect them on April 2 (ϕ = 0.04), May 5 (ϕ = 0.09), May 8 (ϕ = 0.09), or on June 5, 2010 (ϕ = 0.13) within the upper limits of our KVN observations. After restarting our monitoring observations, we detected SiO v = 2, J = 1–0 masers starting on October 20, 2011 (ϕ = 0.83) and detected SiO v = 1, J = 1–0 masers starting on December 22, 2011 (ϕ = 0.92). These results provide clear evidence of the interaction between the shock from the nova outburst and the SiO maser regions of the Mira envelope. The peak emission of SiO v = 1, 2, J = 1–0 masers always occurred at blueshifted velocities with respect to the stellar velocity except for that of SiO v = 1 at one epoch. These phenomena may be related to the redistribution of SiO maser regions after the outburst. The peak velocity variations of SiO masers associated with stellar pulsation phases show an increasing blueshifted trend during our monitoring interval after the outburst.

• 천문학회보
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• 제27권2호
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• pp.40-40
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• 2002

• 천문학회보
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• 제27권1호
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• pp.47-47
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• 2002