A Report on New VGOS Frequency Sequences Test Observations

The IVS VGOS Technical Committee (IVS VTC) discussed several times on how to maximize the benefits of VGOS for geodesy and astrometry. Unused potential for improvement was identified in (a) increasing the synthesized bandwidth per VGOS observing band from 480 MHz to 1024 MHz, and (b) distributing the four VGOS frequency bands between 3 and 14 GHz instead of only up to 10.6 GHz as is currently the case. In order to demonstrate the feasibility and possible benefits by using that potential, a series of fringe tests and test sessions were carried out in late 2024, and further tests are planned for early 2025. The results of these tests are expected to provide important input to the efforts of the IVS to anchor the observed frequency channels in the ITU Radio Regulations, so that in the future more consideration could be given to VGOS radio telescopes with regard to unwanted radio radiation. To this end, the optimum VGOS frequency configurations are being sought, as they are to be used in the long term. On behalf of the group members, who carried out these tests, we will report on the performance of these sessions and present preliminary results and recommendations for suitable frequency setups, if possible.