(RF) Generally referring to any frequencies at which the radiation of electromagnetic energy is possible. Also used as designation for frequencies at which the radiation of electromagnetic energy is possible. Also used as designation for frequencies below approximately 50 to 100 Mhz (100 - 300 Mhz is very high frequency, 300 Mhz - 1000 Mhz is ultra-high frequency, 1000 MHZ and up is microwave).