Increase in Interference Levels in the 45 ? 870 MHz Band at the Spanish e-CALLISTO Sites over the Years 2012 and 2019 - Prieto, M.; Gordo, J.B.; Rodríguez-Pacheco, J.; Martínez, A.; Sánchez, S.; Russu, A.; Monstein, C.; Fernández, R. (Solar Physics, 2020)