In order to activate the sound signal, you need to key the mic five times on a designated frequency. Provided that you within VHF range, the AtoN will begin blaring sound signals at its designated intervals. Each MRASS will be on a different VHF frequency. Authorized channels include 81A and 83A; however, if those frequencies are used as working channels in a port, a different frequency will be designated. The correct frequencies will be placed on current NOAA nautical charts. While the NOAA no longer provides printed charts, you can download PDFs of the most up-to-date charts at NOAA/charts.