KDX-87 RECEIVING AND ANALYSING SYSTEM FOR VLF WIDE-BAND DIRECTION FINDING
TIAN MAO Xu JI-SHENG MA SHU-YING(Deft, of Space Physics, Wuhan University, Wuhan 430072)
The KDX-87 receiving and analysing system for VLF wide-band direction finding (DF) developed by whistler group of Wuhan University is described. This system is suitable for measuring and analysing the exit area, polarization state and dynamic spectrum of whistler waves, and can be extended to locate the long-distance lightning and VLF navigation signals etc.. The system has the following advantages: 1. Snail size antennas and portable receiver are adopted, which makes it convenient to take and set up the receiving system in the field. 2. The coupling and balancing circuits between antennas and receiver are properly designed and an effective calibration technique is used, thus enabling the system to have a good frequency response and an uniformity of properties between different channels. 3. By utilizing the frequency-modulation characteristic of whistler signals, frequency-tracking wide-band DF is realiz-ed; in comparison with the traditional method of narrow-band DF, the DF errors produced by multipath effects are greatly minimized and additional information on the relationship be- tween wave frequencies and exit points of whistler path can be obtained. 4. A digitized goniometer is developed as a result of improving the traditional analogue goniometer. With a coordinate use of two methods of goniometer and field-analysis, satisfactory DF results can be obtained under either conditions of long and short distance between whistler exit and receiver. 5. The whistler dynamic spectra are analysed through a microcomputer with an effective process of removing interferences performed in advance, and the resulted spectrograms show much better resolution than that made by an ordinary sonagraph. By using the KDX-87 system, some valuable DF results have been got in the low-latitude whistler DF experiments which were carried out cooperatively by Chinese and Japanese researches.