A day in which sunspot activities or ionospheric disturbances do not interfere with radiocommunications. Note: Ionospheric disturbances created in electronic systems may be coupled into fiber optic transmission systems, especially when they are connected to radio links. See also  connection,  coupling,  disturbance,  electronic,  fiber optic transmission system,  ionosphere,  interference,  radiocommunications,  radio link,  sunspot,  sunspot activity,  system.