Carrillo-Vargas A. 1 , J. A. González- Esparza 1 , E. Andrade, E. Aguilar-Rodriguez 1 , G. Casillas 1 , R. Pérez- Enríquez. 2 , S. Kurtz 3 , S. Jeyakumar 4 , P. Sierra 5 , S. Vázquez 5 , Selvanayagam 6 , G. Sankar 6 , Sureshkumar 6 , and C. Gutiérrez 7 . THE MEXART IPS OBSERVATIONS IN ROUTE TO THE MEXART IPS OBSERVATIONS IN ROUTE TO THE NEXT SOLAR MAXIMUM THE NEXT SOLAR MAXIMUM 1 Instituto de Geofísica, UNAM, Ciudad Universitaria, DF, México, 2 Centro de Geociencias, UNAM, Juriquilla, Querétaro, México 3 Centro de Radio Astronomía y Astrofísica, UNAM, Morelia, Michoacán, México. 4 Departamento de Astronomía, Universidad de Guanajuato, México. 5 Instituto de Geofísica y Astronomía, CITMA, Ciudad de la Habana, Cuba. 6 National Centre for Radio Astronomy, Tata Institute of Fundamental Research, Pune, India. 7 Instituto Nacional de Astrofísica, Óptica y Electrónica, Puebla, México. ABSTRACT We report the status of the Mexican Array Radio Telescope (MEXART) in preparation for the next solar maximum. During this epoch, the MEXART will be one of the four dedicated radio telescopes (with the ORT in India; STEL in Japan; and MWA in Australia) to track large-scale structures in the solar wind using the interplanetary scintillation (IPS) technique. This network of IPS observatories will produce, for the first time, four g maps of the sky showing the size and shape of disturbances between the Sun and the Earth. We describe the operation and current observations of the first IPS radio sources at 140 MHz detected by the MEXART. These observations use a plane dipole array of 1024 elements (16 lines with 64 dipoles each one), feeding a Butler matrix of 16x16 ports. This system generates 16 lobes at fixed declinations covering 120 0 (from -40 0 South to 80 0 North). The beam fan uses the Earth’s rotation to cover the whole sky. The observations that will be made with the network of observatories of interplanetary scintillation will complement the observations of other observatories, instruments in situ, space probes, satellites, among others. THE TELESCOPE. The general system scheme of the MEXART can be represented by 6 subsystems: (1) the antenna (see Fig. 2), (2) the low-noise amplifiers system, (3) the Butler matrix, (4) the 16:1 multiplexer, (5) the receivers, and (6) the data acquisition system. (1) THE ANNTENA. The basic element of the MEXART array is the full- wave dipole (!=2.15m) polarized along the East–West geographic direction. The array of dipoles and transmission lines are made of copper cable 14 AWG with PVC spacers to keep the impedance constant. The dipoles and transmission lines are supported by polypropylene poles recycling and nylon cords. The antenna has a reflection screen !/4 below the dipoles. The array has 64 parallel E–W rows and each row has 64 dipoles grouped in four sections (2 east and 2 west) of 16 dipoles. In total, the array has 64x64=4096 elements occupying 9591m 2 . Fig. 4 shows a diagram of the antenna. Each E–W row is separated about !/2 along the North–South direction from the next row. (2) THE LOW-NOISE AMPLIFIERS SYSTEM. The system is behind of each subarray (16 dipoles). The system is underground below the dipoles and the combination system uses a tree configuration. The signal caught by each section is lead through a high-pass filter (84 MHz), later is amplified using an amplifier ZFL500LN with a 28 dB gain. The signals of the two eastern (western) adjacent sections are added by a 2:1 power combiner. Finally, after amplification the RF signal is carried through underground coaxial cables to the receiver room. More details of the ensemble dipoles and technical characteristics of the components can be found in Carrillo [2007]. CONCLUSIONS. -We are on the final phase of the radiotelescope calibration. -At the same time we creating a data base that will be crucial in order to generate the g-maps. -The MEXART will be part of an IPS network dedicated to study large scale disturbances which travel through the interplanetary medium. REFERENCES [1] Carrillo-Vargas A., “Construcción y calibración del radiotelescopio de centelleo interplanetario, MEXART”, PhD. Thesis. Universidad Nacional Autónoma de México, 2007. [2] Gonzalez–Esparza J. A., A. Carrillo-Vargas, E. Andrade, Perez-Enriquez R. and ,S. Kurtz, “The MEXART Interplanetary Scintillation Array in México”, Geofisica International, 43, No. 1, pp. 61 - 73, 2004. [3] Jeyakumar S., A. Carrillo, and E. Andrade “MEXART II: System calibrations and characterisation of system performance”, Institute of Geophysics, UNAM 2006. Figure 4. (A) Electrical diagram of one row with 64 dipole showing the configuration of 4 subarrays of 16 dipoles, 4 baluns, 4 high-pass filters, 2 stages of combination and 2 stages of low-noise amplification. (B) General scheme to the planar array with 64 rows along the North-South. (4) THE MULTIPLEXER. The Butler matrix contributes with 16 output signals. The signals can be processed in two options: a) to send each signal to one receiver, b) to use a multiplexer system 16:1 that sends the output signal of a specific port to a selected receiver. For the calibration tests to the array showed in this poster it was determined to use 16:1 switch with one receiver. (5) THE RECEIVER. We use d a tota l-powe r superhete rodyne rec eive r. The preselector filter is designed with impedances a set of 50_ impedances centered in 139.65MHz with bandwidth of 2MHz. The intermediate frequency filters (IF) have a central frequency of 10.7MHz with a 2MHz bandwidth. For the IF-amplification stage we used the low-noise amplifiers with 24dB gain. The local oscillator has a high stability in the frequency <+-0.05 ppm, a phase of standard noise of -110 dBc/Hz and a power output which ranges from +7 dBm up to +13 dBm, [1]. The mixer used in the front part conforms a doubly balanced mixer (ZFM-1W/MiniCircuits). (6)ACQQUISITION SYSTEM. We are using a acquisition card PCI-6036E of 16 bit with 8 input ports (National Instrument). Once digitized the data are stored in computer files for its later use. The system is running over a Unix-Linux ambient. The programs that are used for the data acquisition are written in C Language. The real time signal of the MEXART can be seen at http://www.mexart.unam.mx. (3)THE BUTLER MATRIX. The antenna, as described in the foregoing section, was designed to be a meridian transit instrument with no steering in declination. If the signals from each row are combined with different increment of phase, the antenna beam will point to a different declination. The Butler matrix [Butler and Lowe, 1961, Shelton and Keller, 1961] achieves this in the most efficient manner by combining the signals from each of the lines in an equal number of different ways to create a set of beams which cover the whole range of declination available to the antenna. The first step in the calibration of the Butler matrix is to test the beam pattern in broadside configuration for each individual E–W row. The main lobe of each row points toward the zenith, the beamwidth in the plane E–W is 1 0 and for the plane N–S is about 120 0 . Fig. 2 shows the 3-D simulated pattern for one row. Fig. 5 shows the theoretical beam pattern associated with a Butler matrix of 16x16 ports. In the MEXART we are using a 16x16 Butler matrix to calibrate the full array. Figure 3. Block diagram and technical characteristics of the IPS-MEXART . THE SITE. Surrounded by a low altitude (<5 0 ) mount ain chain. The MEXART is located in a small village in Coeneo, Michoacan (19 0 48’ N 101 0 41’ W ) that lies at an altitude of 1997 m on the sea level (see Fig 1.). This place is almost free of electromagnetic noise levels at the 138.9-140.4 MHz frequency band [Carrillo et al., 1997]. There are no extreme weather conditions and the place is well connected to some major cities such as Morelia, Guadalajara, and Mexico City. As for high level educational institutions, Michoacan is home of the most important group of radio astronomy in Mexico (CRYA-UNAM, Campus Morelia) and several technological universities and Institutes such as Universidad Michoacana de San Nicholas de Hidalgo, Instituto Tecnológico de Morelia, among others, which are collaborating in this project. FIGURE 1. Map of Mexico and the site of the MEXART in Michoacan (19 0 48 ’ north and 101 0 41’ west). The MEXART will be a member of the network of IPS observatories dedicados de tiempo completo a estudios del viento solar y clima espacial. Figure 2. Panoramic view of the Mexican IPS telescope. In the image are appraised: a section of the dipole array, the control room, laboratories, among others. Figure 5. 3-D Theoretical pattern beam of one row with 64 elements. Figure 6. Theoretical Pattern beam of Butler matrix 16x16 ports. ACKNOWLEDGMENTS We are very grateful to Prof. Rajaram Nityananda Director of the National Centre for Radio Astrophysics for their generous support and assistance to the project. (A) (B) Figure 7. (A) Picture of the Butler matrix and receivers. (B) Detail of multiplexer. (C) Butler matrix and multiplexer. (D) Multiplexer`s control and receivers. A B C D Figure 8. Theoretical patterns beam associated with a 16x16 Butler matrix. OBSERVATIONS. We are using subarrays with 16 lines each, a Butler matrix of 16x16 por ts, a 16:1 multiplexer and a superheter odyne receiver. The observations of calibration are obtained every 24 hours, and for each day we select a beam, that is to say, a fixed declination is selected. Records of amplitude versus time are obtained. Every day the series are analyzed to obtain the stellar radio sources and their main parameters: amplitude, transit time, Sky-noise, interferences, among others. The calibration of the telescope will be realized applying this routine. We show typical plots of the observations obtains with this set-up, see Fig. 10, 11 and 12. Figure 9. Radio-sky observed with MEXART. Each trace is associated with a Beam-output of matrix Butler. Figure 10. The plot shows the power level detected by a lobe of the matrix of Butler with 8 0 (HPBW) and declination of 40 0 . Figure 11. Collection of plot showing the typical radio sources observed with different beams of the 16x16 matrix.