to comply with various legal requirements. There might also be similar regulations for the segment of the cable that must run outdoors. The antenna must be located on a high position with a clear (as possible) view of the sky. Fur- thermore, it must be placed at a distance away from other antennas and especially away from other sources of radiated energy. The antenna may even require some form of shielding to pro- tect it from the ingress of electromagnetic interference (EMI). Finding the best location for GNSS signal reception is not as obvious as one might think; experience is required. In many buildings, an installer needs to be certified (occupational health and safety) to get ac- cess to restricted spaces, like internal cable ducting and rooftop areas. There can be somewhat dangerous equipment on rooftops, such as microwave transmitters. The antenna installation needs to incorporate surge protection to protect people and equipment in the building from the ingress of dangerous sources of energy, such as lightning. This is a seri- ous safety-of-life issue if not done correctly. For similar reasons, when playing around with an off-the-shelf consumer antenna, do not place it up high or leave it outside, especially in stormy weather conditions. Finally, the antenna installation should be surveyed for accurate position and height to ensure the antenna is receiving a valid signal and not a multipath signal reflected off a nearby structure. Similarly, the length of antenna cable should be determined and the GNSS receiver calibrated to compensate for that cable length. For all those reasons, the authors recommend operators of GNSS equipment that need a reliable and accurate source use a local professional to design and install GNSS antennas. For further informa- tion on deploying a solution based on GNSS versus other approaches, refer to Chapter 11. There is also an ITU-T document, "GSTR-GNSS Considerations on the use of GNSS as a primary time ref- erence in telecommunications," that contains useful information on th