A relatively inexpensive 16 Gbps data-recording system based on commercial off-the-shelf technology and open-source software has recently been developed. Combining this recorder with the parallel development of broadband Very Long Baseline Interferometer (VLBI) instrumentation is enabling dramatically improved sensitivity for both astronomical and geodetic VLBI. In this article, we describe the VLBI system and the results of a demonstration experiment that illustrates a number of cutting-edge technologies that can be deployed in the near future to significantly enhance the power of the VLBI technique.

The recent development of a relatively inexpensive 16-Gbps data-recording system based on commercial off-the-shelf technology and open-source software, along with parallel development in broadband Very Long Baseline Interferometry (VLBI) techniques, is enabling dramatically improved sensitivity for both astronomical and geodetic VLBI. The system is described, including the results of a demonstration VLBI experiment that illustrates a number of cutting-edge technologies that can be deployed in the near future to significantly enhance the power of the VLBI technique.

For the purpose to be used in correlation processing and data analysis of VLBI application in spacecraft navigation, relativistic VLBI delay model for finite distance radio source was developed. This delay model has precision of a pico second or better for any spacecraft including even low earth orbit satellite with 100km altitude. The formula of delay expression is in quite similar form with the consensus model, which is standard VLBI delay model. Thus it is relatively easy to be implemented in the current VLBI analysis packages. Detailed derivation procedure of the delay model is described in this paper (Part I). Delay rate and partial derivative with respect to radio source coordinates and station coordinates will be described in the paper part II in the next issue.