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
10-meter band repeater channels, "odd-splits" (offsets differing from 100 kHz) and non-standard frequencies are not uncommon. Since 10 meters can frequently open up to propagate globally, most 10-meter repeaters use a CTCSS sub-audible access tone. 16 kHz wide signals with 5 kHz deviation is normal in this band. 8 kHz narrow signals with 2.5 kHz deviation can also be found. 29.300 MHz is a common frequency to find JA hams on. British hams commonly use the 29.400 to 29.500 MHz band for FM as well with 29.400, 29.450, and 29.500 MHz being common. USA hams can be found on FM anywhere above