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
160-meter band 160-meter band Just above the mediumwave broadcast band, 160 meters refers to the band of radio frequencies between 1800 and 2000 kHz. For many decades the lowest radio frequency band allocated for use by amateur radio, before the adoption, at the beginning of the 21st century in most countries, of the 630 and 2200 meter bands. Older amateur operators often refer to 160 meters as the Top Band It is also sometimes referred to as the "Gentleman's Band" in contrast to the often-freewheeling activity in the 80 and 20 meter bands. The 160 meter band is the oldest amateur band