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장동희(Jang Dong-Hee) 서울행정학회 2003 한국사회와 행정연구 Vol.13 No.4
Dasan insisted fundermental reformation of personnel administration of Choseon Dynasty two hundred years ago. Gyengseyupyo, one of his famous books, contained these insistences: restructuring bureaucratic hierarchy system, downsizing bureaucrats and organizations, renovating Gangwan institution, reforming selection and examination of bureaucrats, and refreshing evaluation system about personnel.
효율 평탄도 개선을 위한 20 W 고선형 광대역 2단 VHF/UHF 전력 증폭기의 설계와 구현
장동희(Dong-Hee Jang) 융복합지식학회 2020 융복합지식학회논문지 Vol.8 No.3
본 논문에서는 다양한 무선 통신 시스템의 통합을 위해 30-500 ㎒의 동작 주파수를 가지는 20 W 2단 VHF/UHF 전력 증폭기를 설계하고 구현하였다. 낮은 주파수 대역에서 효율 평탄도를 개선하기 위해 공진을 조정할 수 있는 부궤환 회로를 제안하였다. 전력 증폭단은 동축 케이블 발룬을 적용한 푸시풀 구조를 사용하였고 전치왜곡 구동단을 적용하여 2단 전력 증폭기의 선형성을 최적화하였다. 제안된 전력 증폭기를 검증하기 위해서 2-tone 테스트 신호를 사용하여 측정한 결과, 광대역 전력 증폭기는 30~500 ㎒ 대역에서 평탄화된 이득, 출력 전력, 효율, 선형성 특성을 얻었다. 제안된 설계 방법을 토대로 구현한 2단 VHF/UHF 전력 증폭기는 디지털 전치왜곡기와 결합되어 높은 선형성을 얻을 수 있었다. In this paper, the 20 W 2-stage VHF/UHF power amplifier is designed and implemented for integrating various wireless communication systems in a frequency range of 30 to 500 ㎒. The negative feedback circuit with a resonance adjustment is proposed for improving the efficiency flatness at a lower frequency band. The power amplification stage utilizes a push-pull structure with a coaxial cable balun. The drive amplification stage operates as a predistorter for optimizing the linearity of two-stage power amplifier. For demonstration of the power amplifier’s performance, a 2-tone test signal is used. The broadband power amplifier can obtain the improved flatness characteristics for gain, output power, efficiency, and linearity in a frequency range of 30 to 500 ㎒. From the digital predistortion measurements, the proposed power amplifier can achieve the higher linearity.
장동희(Dong Hee Jang),김재원(Jae Won Kim),안은영(Eun Young Ahn) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
Comprehensive experimental works are carried out for the optimal design of a centrifugal blower adopted in an indoor unit of an air-conditioner. the models for consideration are typical multi-blade turbo blower and limit loaded one, respectively. The main interest lies on the fluid dynamics performance when the blower is installed in the practical system. the methodologies are an experimental estimations with a wind tunnel for blower performance and static pressure rise and the reason is explained by the precise measurement of the flows between blades using PIV. Consequently, it is found that the blower is proper for the flows with a resistance in down stream such as a heat exchanger.
김재원,장동희,안은영,Kim Jae-Won,Jang Dong-Hee,Ahn Eun-Young 한국유체기계학회 2006 한국유체기계학회 논문집 Vol.9 No.3
Comprehensive experimental works are carried out for the optimal design of a centrifugal blower adopted in an indoor unit of an air-conditioner. The models for consideration are typical multi-blade turbo blower and limit loaded one, respectively. The main interest lies on the fluid dynamics performance when the blower Is installed in the practical system. The methodologies are an experimental estimations with a wind tunnel for blower performance and PIV measurement for the detail flow information. A centrifugal blower with limit loaded fan shows pronounced performances in terms of the flow rate and static pressure rise and the reason is explained by the precise measurement of the flows between blades using PIV. Consequently, it is found that the blower is proper for the flows with a resistance in down stream such as a heat exchanger.
김진민(Jin Min Kim),김재원(Jae Won Kim),장동희(Dong Hee Jang),금경필(Kyung Pil Kum),박상욱(Sang Wook Park),김병진(Byung Jin Kim) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
Comprehensive experimental works are carried out for the optimal design of a turbo blower adopted in an indoor unit of a handy vacuum cleaner. Impeller and its auxiliary structure are very important factor for the performance of it. The main interest lies in the fluid dynamics performance when the blower rapidly rotates in a product system. The estimations of blower performance was performed by using the wind tunnel and PIY measurement for the detail flow information of outlet side. The turbo fan shows the performances in terms of flow rate and suction pressure are important factor in a vacuum cleaner. It is found that the reduced area and inclination of fan base-plate increases the flow rate and efficiency.