• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.4
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• pp.73-79
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• 2002

In this paper, electromagnetic waves radiated from discharge at three-type electrodes(needle-plane, plane-plane and sphere-plane electrode) using AC power source in air are measured and the peculiar patterns of their spectra are reported. The radiated electromagnetic waves were measured in bandwidth of VHF(30-230[MHz]) using a biconical antenna and a spectrum analyzer. When the discharge onset voltage range, high electric field intensity is shown in frequency band of 45, 70, 80[MHz] in case of needle-plane electrode configuration and 40[MHz] in case of plane-plane and sphere-plane electrodes configuration. However, when the breakdown voltage range, the frequency spectrum distribution of radiated electromagnetic waves appear different in the whole frequency range according to the shapes of electrode.

• Proceedings of the KIEE Conference
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• 2001.11a
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• pp.219-223
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• 2001

In this paper, electromagnetic waves were measured in accordance with propagating the discharge when positive and negative DC high voltage was applied to needle-plane electrdes and plane-plane electrdes that solid dielectric was inserted between the electrodes. The radiated electromagnetic waves were investigated in bandwidth of VHF($30{\sim}230$[MHz]) using an biconical antenna. In needle-plane electrodes high electric field intensity is shown in both frequency band of 90(MHz) and 170[MHz], and gradually decreasing characteric is appeared at high frequency band. However high electric field intensity is shown in both 80[MHz] and 140[MHz] in case of plane-plane electrodes configuration. And over 150[MHz] frequency band, rapidly decreasing characteristic is shown. Moreover, electric field intensity of positive DC is about $5{\sim}10$[dB] higher than negative DC.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.1
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• pp.27-32
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• 2019

This study describes the design and implementation of a simulated signal generator to demonstrate the performance of VHF band radar for the detection of small targets in RCS(Radar Cross Section). The transmission and reception antenna beam widths used in the simulated signal generating apparatus may be large, which may cause problems in the degree of isolation. Interference signal immunity and isolation characteristics are improved by considering operating conditions of VHF radar to solve isolation of antennas. Simulated signal generator performs the following: VHF radar transmission and reception correction, simulation signal generation, target Doppler, RCS and distance simulation, remote control, and GPS clock synchronization function. After the fabrication of the simulated signal generator, the main characteristics, such as the output characteristics and the reflection signal simulations, were tested. When the microwave radar assembly is completed in the future, it will be utilized for the performance evaluation of VHF radar.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.3
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• pp.159-166
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• 2018

Herein, a non-Foster matching circuit is designed to improve the impedance matching characteristics of small antennas in the VHF and UHF bands. The proposed non-Foster circuit is designed to operate with negative capacitance in a wide frequency band from 50 MHz to 1,000 MHz for use in various communication bands. To ensure the stability of the non-Foster circuit with conditional stability, the open-circuit stability condition of Linvill was satisfied, and the circuit was fabricated using the FR-4 substrate. The fabricated non-Foster circuit was combined with a small antenna to verify its performance by measuring the return loss and received power in the FM, DMB, and GSM bands. The measured return loss was improved from -6 dB to -30 dB, and the measured received power was improved from 0.5 dBm to 5.2 dBm.

• The Journal of the Acoustical Society of Korea
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• v.23 no.4E
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• pp.120-124
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• 2004

A new type of high frequency wideband ultrasonic transducer with a separation between a transmitter and a receiver was proposed and its characteristics were simulated using a PSpice model. The piezoelectric ceramic $PbTiO_{3}$ as a transmitter and the piezoelectric copolymer P(VDF- TrFE) as a receiver were used for high sensitivity and wide bandwidth, respectively. The characteristics of the focusing transducer with center frequency of approximately 35MHz fabricated in this study showed very wide bandwidth, which could give an axial spatial resolution better than $30{\mu}m$ in B-mode image for biological tissues.

• Journal of the Korean Institute of Telematics and Electronics
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• v.13 no.6
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• pp.12-15
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• 1976

This paper presents the realization method of 90$^{\circ}$ constant phase shifter in the VHF band, constructed by the entirely differens idea from the conventional method of the realization of constant phase shifter in the audio frequency range. The construction of 90$^{\circ}$ constant phase shifter is. simple and can be easily realized by using the distributed constant element, transmission line, and the lumped constant elements, R,C,L.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.104-107
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• 2003

본 논문에서는 VHF대역 기지국용 전력증폭기에 대해 입력레벨이 $0dBm{\pm}1 dB$, 출력이 $45dBm{\pm}1dB$인 증폭기를 모듈화 하여 설계하고 제작 및 측정하였다. 출력 레벨 제어는 Pin Diode 감쇄기를 이용하여 Dynamic Range 40dB 내에서 5단계로 전력제어가 가능하고 입력레벨이 $-4{\sim}0dBm$로 변동될 때 AGC(Auto Gain Control) 회로가 동작 되도록 설계하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.10
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• pp.1999-2007
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• 2017

In this paper, we implement a multi-band network selection (MNS) system based on Linux operating system which determines the optimal communication link for given network conditions among the available LTE, very high frequency (VHF), and high frequency (HF). The implemented software consists of a network interface, an MNS server, and a user GUI. We perform indoor test to verify the function of the implemented MNS system using two sets of MNS system. To this end, two types of VHF communication links that follow ITU-R M.1842-1 Annex 1 and Annex 4 are emulated in software. In addition, the HF transmission (reception) port of one MNS is directly connected to the HF reception (transmission) port of another MNS. We demonstrate through indoor tests that the implemented MNS system can support seamless maritime communication service in spite of artificial disconnection or re-connection of LTE, VHFs, and HF. The implemented MNS system is applicable to various maritime communication services including e-navigation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.9
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• pp.992-999
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• 2008

This paper describes the design of SPST PIN diode switch which has a 2 kW high power handling capability within $50{\mu}s$ switching speed in $20{\sim}100$ MHz VHF-band. Design factors were investigated and it was confirmed by simulation that the characteristics of insertion loss, VSWR, and isolation met design goal. Also, the capability to handle 2 kW high power with maximum fast switching speed less than $20{\mu}s$ was confirmed and insertion loss less than 0.2 dB, VSWR less than 1.17:1, and isolation higher than 40 dB were obtained by experiments.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.1117-1124
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• 2005

The radio field environment is very different according to frequency band, therefore communication condition is equation that VHF is passed by direct radiation and HF is via reflect radiation in ionosphere. Load a ship according to the enforcement regulations of the ships safety act have specificated the radio equipment that should be operating. This paper have analysed by the simulation program about radio field environment for research the communications condition, which is VHF & HF band in domestic coastal. We have Predicted to radio field environment and communications condition using the data of analysis and domestic radio regulation regard to coast navigational ship. Therefore have proposed the necessity for rationally plan on improvement the radio regulation and network cooperation of VHF radio station.