The Geodetic Sites host two active hydrogen maser that are used as the master frequency reference for the station. The peculiarity of this kind of atomic clock is that it reaches the best frequency stability we know of, a characteristic needed in VLBI observations to preserve a long coherence time in high frequencies. A set of two maser are used as a backup system, because VLBI observations without such a reference are not possible. They are hosted in an isolated chamber environmentally controlled in temperature, and monitored in pressure and humidity.
Maser isolation package
Due to the incoherent nature of VLBI as an unconnected interferometry technique, it requires the best possible accuracy and stability in frequency standards to keep the coherence between two remote stations over the longest integration period achievable to improve the sensitivity of the instrument. A typical active H-maser has an Allan Variance better than 10-13 in one second, which is the typical integration time during the correlation of VLBI observations.
Front service panel
Yebes Observatory host two active Hydrogen maser. Santa Maria has an hydrogen maser (H-MASER) and a iMaser from T4Science.