Ultrasound independent Advisory Group on Non-ionising Radiation (AGNIR) produced a report in 2010, which was published by the UK Health Protection Agency (HPA). This report recommended an exposure limit for the general public to airborne ultrasound sound pressure levels (SPL) of 70 dB (at 20 kHz), and 100 dB (at 25 kHz and above). Ultrasound Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies from person to person and is approximately 20 kilohertz (20,000
6-meter band general agreement among the amateur radio community, 200 kHz of the 6-meter band is reserved for the telecommand of models, by licensed amateurs using amateur frequencies. The sub-band reserved for this use is 50.79 to 50.99 MHz with ten "specified" frequencies, numbered "00" to "09" spaced at 20 kHz apart from 50.800 to 50.980 MHz. The upper end of the band, starting at 53.0 MHz, and going upwards in 100 kHz steps to 53.8 MHz, used to be similarly reserved for RC modelers, but with the rise of amateur repeater stations operating above 53 MHz in the United States, and