The Brazilian National Telecommunications Agency (ANATEL) has published Official Letter 81/2025, intended to clarify and harmonise the definition of indoor environments, particularly in vehicle applications, for the 5150-5350 MHz band under clauses 3.1.48 and 11.2 of Act 14448.

Under ANATEL's definition, an indoor environment is one in which the obstruction of a building attenuates the transmitted signal and thereby reduces emissions in multiple directions, as defined in clause 3.1.1 of Act 14448. On that basis ANATEL has determined that the 5150-5350 MHz band (WLAN B1/B2) may only be used in vehicles with a fully enclosed structure that simulates an indoor environment, such as cars and trucks. The band may therefore not be used in open vehicles, including motorcycles and convertibles.

1. Acknowledging receipt of Official Letter OFFICIAL_SEI_COMMITTEE OCDS_057_25, number 13205985, SEI process 53500.006776/2025, requesting guidance from ANATEL on the application of items 3.1.48 and 11.2 of the Technical Requirements for Conformity Assessment of Restricted Radiation Radiocommunication Equipment approved by Act 1448/2017 with respect to motorcycles and convertibles.

2. Considering sub-clause 3.1.1 of the Technical Requirements annexed to Act 14448/2017, which defines an enclosed environment (indoor) as an environment capable of attenuation through the obstruction of a building so that the emission levels of a transmitter are reduced in multiple directions.

3. Considering sub-items 3.1.48 and 11.2 of the annex to Act 14448/2017:

3.1.48. Land transport vehicles: vehicles used to transport goods or people whose interior is considered an enclosed environment (indoor) for the purposes of this document. This item also applies to trains.

11.2. The following provisions apply to access point transceivers in the 5,150-5,350 MHz band installed inside land transport vehicles and trains.

The above rules do not apply to the vehicles in question, since they cannot guarantee the presence of obstacles capable of reducing the transmitter emission level in different directions.