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
500 kHz kHz to amateur radio use. In Belgium, amateurs are allocated a 501 to 504 kHz on a secondary basis on January 15, 2008. Only CW may be used with a maximum ERP of 5 W. In Norway, the band 493–510 kHz was allocated to radio amateurs on November 6, 2009. Only radiotelegraphy is permitted. In New Zealand, the band of 505 to 515 kHz was allocated temporarily, pending an international frequency allocation. In the Netherlands Amateur radio operators have allocated the band from 501–505 kHz with a maximum of 100 watts PEP on January 1, 2012. 500 kHz The radio