• Publications of The Korean Astronomical Society
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• v.14 no.1
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• pp.39-45
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• 1999

We have carried out measurements of 1.2-1.6GHz radio interferences around Seoul Radio Astronomy Observatory located in the campus of Seoul National University. We received interference signals using a pyramidal horn antenna and measured its power using a spectrum analyzer with 1MHz resolution after $\~60dB$ amplification. In order to check the spatial characteristics, we made observations at every $30^{\circ}$ in azimuth at elevation of $30^{\circ}\;and\;60^{\circ}$. Also, in order to check the temporal characteristics, we repeated the all-sky observations five times at every six hours. The results may be summarized as follows: (1) There are strong $({\geq}-20dBm)$ interferences between 1.2 and 1.4GHz. Particularly strong interferences are observed at 1.271 and 1.281GHz, which have maximum powers of -0.34dBm and -0.56dBm, respectively. (2) The characteristics of the interferences do not depend strongly on directions, although the interferences are in general weak at high elevation and in east-west direction. (3) The interferences appear for a very short $(\leq0.01s)$ period of time, so that the average power is much smaller than the maximum power. Strong interferences with large $(\leq-49.0dBm)$ average power have been observed at 1.271, 1.281, 1.339, and 1.576GHz. At these frequencies, the interferences appear repeatedly with a period of $\leq0.1s$ By analyzing the observed power, we find that, for the strongest 1.271GHz interference, the average intensity is $-171dBW/m^2/Hz$ and that the maximum intensity is $-122dBW/m^2/Hz$. If this interference is delivered to the detector without any shielding, then its power would be much greater than the rms noise of a typical line spectrum. Therefore, it is important to shield all the parts of receiver carefully from radio interferences. Also, without appropriate shielding, the sensitivity of a receiver could be limited by the interference.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.2
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• pp.271-279
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• 2008

In this paper, we investigate interference between short-range radiocommunication devices(SRDs) with frequency hopping spread spectrum(FHSS) and direct sequence spread spectrum(DSSS) methods when they are in the same frequency bands. In order to analyze interference from unwanted emission of SRD with DSSS to that of FHSS, Monte-carlo(MC) simulation method is employed and interference probabilities are calculated. We simulate interference scenarios in accordance with several duty cycles and bandwidths. It is also assumed that the propagation model is free space. The effect of distance between interfering transmitter and victim receiver is analyzed and bit error rate(BER) is simulated. From the interference analysis results, it is shown that duty cycle affects compatibility more than band-width does. Also, we can make sure of the separation distance which satisfies BER criterion when there are only one interfering transmitter and multiple interfering transmitters.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.11
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• pp.45-52
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• 2005

In this paper, we propose the PLL system of the local oscillator system for the millimeter wave band's radio astronomy receiving system. The development of the proposed local oscillator system based on the YIG oscillator VCO with $26.5\~40GHz$ specification. This system consists of the oscillator part including the YIG VCO, the harmonic mixer, and the isolator, the RF processing part including the triplexer, limiter, and RF discrimination processor, and the PLL system including YIG modulator and controller. Based on this configuration, we verify the frequency and power stability of the developed local oscillator system according to some temperature variation. From this test results we confirm the stable output frequency and power characteristic peformance of the developed LO system at constant temperature.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.5
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• pp.501-509
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• 2010

In this paper, the interference avoidance performance of the RFID reader with the compressive receiver was analyzed. In the environment of the multiple dense readers operating, the recognition rates of the conventional RFID reader and the proposed RFID reader with the compressive receiver were measured and compared. The recognition rate of the proposed reader was improved more than 2.7 times compared to the conventional reader. Especially, in the environment of two proposed RFID readers operating simultaneously, little degradation of the recognition rate was observed.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2002.11a
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• pp.16-20
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• 2002

This paper describes the resistive FET mixer with low IF for the 4-Ch DBF(Digital Beam Forming) receiver with LNA(Low Noise Amplifier). This DBF receiver based on the direct conversion method is generally suitable for high-speed wireless mobile communications. A radio frequency(RF), a local oscillator(LO) and an intermediate frequency(IF) considered in this research are 2.09 ㎓, 2.08 ㎓ and 10㎒, respectively. The RF input power, LO input power and Vgs are used -10㏈m, 6㏈m and -0.4 V, respectively. In the 4-Ch resistive FET mixer with LNA, the measured IF and harmonic components of 10㎒, 20㎒, 2.09㎓ and 4.17㎓ are about -12.5 ㏈m, -57㏈m, -40㏈m and -54㏈m, respectively. The IF output power observed at each channel of 10㎒ is about -12.5㏈m and it is higher 27.5 ㏈m than the maximum harmonic component of 2.09㎓. Each IF output spectrum of the 4-Ch is observed almost same value and it shows a good agreement with the prediction.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.36.1-36.1
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• 2010

The Redshift Search Receiver (RSR) is a sensitive, ultra-wideband spectrometer that is being built at the University of Massachusetts as one of the facility instruments for the 50-m Large Millimeter Telescope (LMT). It consists of four receivers each covering the entire 3 mm window from 74 to 111 GHz instantaneously. The primary goal of the receiver is to detect multiple molecular lines in galaxies at any distance and uniquely determine the redshift, in particular dust-obscured star forming systems at high-z which are not easily accessible. I will present some results from commissioning of the RSR on the Five College Radio Astronomy Observatory 14-m telescope, and discuss the future of the receiver.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.5
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• pp.39-45
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• 2019

Recently, Cognitive radio (CR) has been focused for the effective utilization of the limited spectrum. Since an overlay CR system shares the given spectrum with the unlicensed system simultaneously, its spectral efficiency is high. However, most of the studies on an overlay CR system have been focused on the performance enhancement of the licensed receiver (LR). Correspondingly, the performance of the unlicensed receiver (UR) is degraded. Therefore, we propose an overlay CR NOMA system to improve the performance both of the LR and UR, which has a selected relay for the UR and adjusts the power allocation for the LR. The analytical performance of the proposed system is derived and verified the results through simulation. It is noticed that the UR can be obtained signal-to-noise ratio (SNR) gains by the selected relay, consequently, the system performance can be improved. Also, we show that the performance of the proposed system can be controlled by the number of the relays as well as the power allocation ratio. The results reveal that the required performance of the system can be satisfied with the use of the selected relay under the limited transmit power.

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.103-106
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• 2005

The Submillimeter Array (SMA), a collaborative project of the Smithsonian Astrophysical Observatory (SAO) and the Academia Sinica Institute of Astronomy & Astrophysics (ASIAA), has begun operation on Mauna Kea in Hawaii. A total of eight 6-m radio telescopes comprise the array with currently working receiver bands at 230, 345, and 690 GHz. The array will have 8 receiver bands covering the frequency range of 180-900 GHz. The backend is flexible analog-digital correlator with a full bandwidth of 2GHz, which is very powerful to cover several line emissions simultaneously. The current status and future plans of the SMA are described with emphasis on Taiwanese efforts.

• Journal of KIISE:Computing Practices and Letters
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• v.12 no.2
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• pp.102-110
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• 2006

This paper explains the design and development of the stand-alone high sound quality Internet Radio system, which is aimed for a small embedded type audio device rather than a general PC type. This device is designed to work with an Internet connection. This kind of system is not standardized so far, and also the related algorithm is not open to the public. So it is necessary to analyze several receiving algorithms of current radio receivers, and develop our own hardware in order to overcome these obstacles, finally to get the high quality of sound radio. The main electronic components of this Internet Radio are TCP/IP interfaces, an audio MP3 decoder, an I/O interface, and a Flash Memory Card with advanced audio multicasting for the next-generation Internet Radio. Basic structures and implementation issues of the next-generation most-versatile digital music player, and Internet Radio receivers, are discussed.

• Publications of The Korean Astronomical Society
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• v.18 no.1
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• pp.51-60
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• 2003

This paper is the research and development including the system design and the prototype system building of the 400MHz wide-band digital autocorrelation spectrometer system for radio astronomy observation, which will be used as back-end signal processing unit of the Dual channel SIS receiver at Taeduk Radio Astronomy Observatory. So in this paper, we performed development of the high speed digitizing sampler, the circular memory buffer, and the correlator module for the 400MHz wide-band digital autocorrelator. This developed system will be use at TRAO after the housing and some calibration.