For directly linking the dynamical reference frame of satellite orbits to the quasi-inertial reference frame of extra-galactic radio sources, observations of satellites with the Very Long Baseline Interferometry (VLBI) technique are the only conceivable method. Hence, the satellite observations should be embedded in VLBI network sessions during which also natural radio sources are observed. For this reason, it would be most practical if the artificial signal generated at the satellite for VLBI observations covers the same frequency bands as regularly observed by VLBI radio telescopes and should have a similar flux density across the observed bandwidth as these natural sources. The use of satellites of Global Navigation Satellite Systems (GNSS) such as the Galileo system is advisable because they are well monitored in terms of precise orbit determination and the altitude allows common visibilities of many VLBI telescopes. So far, signal generation on a GNSS satellite dedicated to VLBI observations has not been realized yet, partly because suitable signal generation equipment has not been considered in depth. In addition, many aspects, such as legal implications and technical complications, have not yet been addressed. In this publication, we compiled various aspects of generating an artificial VLBI signal on a GNSS satellite. We describe the legal and technical aspects of generating and emitting an artificial signal on a Galileo satellite suitable for VLBI observations including a design study for the necessary equipment on the satellite. Since geodetic VLBI is currently in a transition period from traditional observations at S and X band to the broadband VLBI Global Observing System (VGOS), the proposed equipment generates a signal suitable for both frequency setups. We have also considered the restrictions for installation on a satellite, such as power consumption, weight, and size. The equipment mainly consists of three devices: noise source, amplifier, and antenna. A diode is used as the noise source. This noise is amplified by a set of low noise amplifiers and then radiated by a spiral antenna. The diode and the amplifiers were chosen from the market, but the antenna was newly designed and simulated. The output signal of this chain was tested using a VLBI baseband data simulator, then correlated and fringe-fitted for validation. The instrumentation proposed here is easy to be constructed, but will still have to be tested in the laboratory together with the instruments on the actual satellite.

为了将卫星轨道的动态参考系直接链接到河外射电源的准惯性参考系，使用甚长基线干涉测量 (VLBI) 技术观测卫星是唯一可行的方法。因此，卫星观测应嵌入到 VLBI 网络会话中，在此期间也观测自然无线电源。出于这个原因，如果卫星产生的用于 VLBI 观测的人工信号覆盖与 VLBI 射电望远镜定期观测相同的频段，并且在观测带宽上应具有与这些自然源相似的通量密度，那将是最实用的。建议使用全球导航卫星系统 (GNSS) 的卫星，例如伽利略系统，因为它们在精确轨道确定方面受到良好监控，并且高度允许许多 VLBI 望远镜的共同可见性。迄今为止，尚未实现在专用于 VLBI 观测的 GNSS 卫星上生成信号，部分原因是尚未深入考虑合适的信号生成设备。此外，法律影响和技术复杂性等许多方面尚未得到解决。在本出版物中，我们汇总了在 GNSS 卫星上生成人工 VLBI 信号的各个方面。我们描述了在适用于 VLBI 观测的伽利略卫星上生成和发射人工信号的法律和技术方面，包括对卫星上必要设备的设计研究。由于大地测量 VLBI 目前正处于从 S 和 X 波段的传统观测到宽带 VLBI 全球观测系统 (VGOS) 的过渡期，因此建议的设备生成适合两种频率设置的信号。我们还考虑了安装在卫星上的限制，例如功耗、重量和尺寸。该设备主要由噪声源、放大器、天线三部分组成。二极管用作噪声源。该噪声由一组低噪声放大器放大，然后由螺旋天线辐射。二极管和放大器是从市场上选择的，但天线是新设计和模拟的。该链的输出信号使用 VLBI 基带数据模拟器进行测试，然后进行相关和边缘拟合以进行验证。这里提出的仪器易于构建，但仍需要在实验室中与实际卫星上的仪器一起进行测试。