What is a primary system that ATIS relies on for communication?

The primary system that ATIS (Automatic Terminal Information Service) relies on for communication is the VHF antenna. VHF, or Very High Frequency, is the standard communication frequency range used in aviation for voice communications, including transmitting essential flight information to pilots. The use of VHF antennas allows for efficient broadcast of information such as weather conditions, runway usage, and other pertinent details that pilots need to know before landing or taking off.

VHF antennas are designed to facilitate clear and reliable communication, ensuring that pilots receive timely updates while in the vicinity of an airport. The other options, while they represent significant technologies in telecommunications, do not specifically pertain to the primary communication method employed by ATIS systems in a typical airport environment. This makes the VHF antenna the correct choice for understanding how ATIS disseminates information to flight crews.