OBSERVATION SFERIC EFFECT ON PROPAGATION VLF SIGNAL USING VLF RECEIVER UKM MALAYSIA Suryadi 1 , M.Abdullah 1,2 , H.Husain 1 1 Department. of Electrical, Electronic and System Engineering, 2 Institute of Space Science, Universiti Kebangsaan Malaysia Email:suryadi@vlsi.eng.ukm.my Abstract− This study aims at investigating the VLF signal disturbance by sferic generating by lightning discharge from the region of UKM Malaysia . This paper reports result the present of VLF line receiver for observation sferic in over Malaysia, The broadband and narrowband data analyzed to observe perturbations of ionospheric D region. Many sferic found that come from radiated the lightning discharge activity can make the amplitude VLF signal changed, also found feature sferic that is ELF 'Slow- Tail,' which is the QTEM (Quasi Transversal Electro Magnetic) sferic component in lower ionosphere over Malaysia. Keywords: VLF , Lightning, Sferics, D-layer ; 1. Introduction VLF (Very low frequency) signal or ground wave that span in the range of 30 Hz up to 50 kHz has been used for remote sensing of the lower ionosphere by researchers (Cummer, S. A et al 1997; Cummer S. A., et al 1998;Carpenter,D. L. 2004). This area of ionospheric D-layer, situated at the altitute of 40-90 km from sea level is mentioned (K.G.Budden,1962). Previous researches on VLF disturbances over the equatorial region are very inadequate, generaly always more concentrated on the mid-latitude and high latitude regions e.g Peter,W.B.,M. Chevalier, and U. S. Inan, (2005), etc. Therefore, this study aims at observing the D- layer VLF wave perturbation over Malaysia which is located in equatorial region. This study would be essential to complement the VLF global observation. VLF receiver can detect disturbance occurs in the D-layer along the transmitter to receiver paths; i.e. lightning discharge effects in which lightning discharge will cause the electromagnetic pulse (EMP) and quasi electromagnetic (qe) fields spreading up and create a wave guide D-layer conductivity distribution of disturbed and destructive signal field VLF (VLF Scattered Fields) (Rodger,C.J.2003; Carpenter,D.L. 2004). Phenomenon that often occurs in the ionosphere is heating of lightning strikes, electron precipitation with magnetospheric electron wave sferics all of above disorders results in amplitude and phase change or distortion to received signal (Rodger 1997; Cummer et al 1997). This paper is a observe work to detect the phenomena regarding the disturbances at D-region using data from VLF receiver organized as broadband and narrowband data using VLF Line receiver detected over Universiti Kebangsaan Malaysia (UKM) Malaysia (2.55 o N,101 o E) or in general, over the equatorial . The Earth’s magnetosphere is capable of sustaining wide variety of signal phenomena. These signals are important partly because they influence the behavior of the magnetosphere and partly because they can be used as an experimental tool to investigate the upper atmosphere. One of the studied wave mode is the sferics mode waves. It is used as a diagnostic tool for the study of disturbance at various D-layer all over Malaysia. Sferics mode radiation consists of electromagnetic waves whose upper frequency cutoff is either the local electron frequency plasma or frequency gyro, whichever is less that is what has been reported by (Stix, 1962). 2. Methodology/Data Analysis Experimental set up installed is consist of two air core wire loop type antennas, a preamplifier and pre- installed VPN (virtual private network) and NI- DAQ7 (Data Acquisition View 7) software (Data Acquisition viewer), VLF receiver and GPS and receiver GPS. The signal coming from the antenna is passed through a VLF band pass filter with a bandwidth of 50 kHz at the preamplifier. It is then fed to a 24 bit PCI-6034E data acquisition Dev1 2.66 GHz computer. The Awesome VLF receiver collects data at full of 100 kHz sampling rate, frequency response of 300 Hz to 47.5 kHz, and 10 microsecond time resolution. The raw broadband and narrowband data is recorded as waveform for post processing in a VLF DAQ viewer. Data obtained from the AWESOME receiver are viewed and analyzed to be used in Matlab programs designed specifically for the VLF data (Standford university,Tutorial 2008). The team of researchers from Stanford University has verified the methodology established in this program so the program can be run properly to view and analyze data from AWESOME receiver. Figure 1. shows block diagram of the system in monitoring ,collecting and storing the data. This initial scientific cooperation is essential in regard of the highly specialized nature of the proposed measurements, which have been pioneered by the researchers at Stanford University.