The invention of radio transmission and reception led to an improvement of navigational technique, making it possible to obtain bearings from reference points obscured by fog or darkness. Radio navigation aids supply the navigators with information that maintains or enhances the safety of navigation. As with communication radios, navigational aids are the electronic devices, the use of which must be carried out by trained and certified personnel. Knowledges of installation, maintenance and proper functioning of the electronic units, as well as their antennas, displays, and any other peripheral devices, are of high imporatnce for safe ships operation.