An Overview of the Japanese GALA-V Wideband VLBI System

NICT is developing a new broadband VLBI system, named GALA-V with aim of frequency comparison between atomic time standards over intercontinental baseline. The development of broadband GALA-V system is coordinated to be as compatible as possible with the VGOS system. Two types of original broadband feed systems were developed for Kashima 34m antenna of modified Cassegrain optics. The first prototype feed named IGUANA-H works at 6.5 16 GHz frequency range and the second feed NINJA works at 3.2 14 GHz range. The GALA-V observation system is designed to capture four bands of 1024 MHz width signal in 3 14 GHz range. Two sorts of data acquisition modes are available. One is narrow channel mode, which acquires multiple channels of 32 MHz width signals. This mode is compatible with the NASA proof of Concept (PoC) system developed by MIT Haystack Observatory. The other is broad channel acquisition mode, in which signal of 1024 MHz width is digitized as a single channel. Radio frequency (RF) direct sampling technique was used in this mode as a new approach for broadband observation with taking advantages of high speed sampler K6/GALAS and its digital filtering function. This technique has several advantages in precise delay measurement by broadband bandwidth synthesis. VLBI Experiments were conducted between Kashima 34m antenna and Ishioka 13m VGOS station of GSI of Japan. The first broadband observation over 8 GHz bandwidth was successful on this baseline in early 2015. Result of the broadband bandwidth synthesis over 8GHz 1. National Institute of Information and Communications Technology 2. National Institute of Advanced Industrial Science and Technology, National Metrology Institute of Japan bandwidth proved sub-pico second resolution group delay measurement in 1 second of integration. Time series of the group delay data shows several pico seconds of fluctuation in a few hundred seconds of time scale. That Alan standard deviation is consistent with frozen flow model of Kolmogorov tropospheric turbulence.

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