AM radio stations will have an additional 180 days to migrate to the FM system. The Ministry of Science, Technology, Innovations and Communications (MCTIC) has extended the deadline to benefit more broadcasters and listeners who follow the programming.
AM stands for Amplitude Modulation. This means that the reach of these stations is expanded compared to FM radio (Frequency Modulation). However, for this reason, these transmissions are more susceptible to interference, which 
compromises the quality of the broadcast. By 2020, the migration is expected to be completed throughout Brazil.
With the signal change to FM, these broadcasters even have the chance for expansion, as they can make digital transmissions accessible via tablets and smartphones. Thus, the service also modernizes with digitization and offers more options for listeners to access the programming.
The MCTIC estimates that 25 million listeners affected by the spectrum will benefit. Another impact of the change is the generation of 750,000 new jobs.
In 2013, the Brazilian government initiated the signal migration process. Since then, 623 broadcasters have already changed their spectrum. With the opening of the new granting process for frequency use, 449 broadcasters are expected to benefit. In total, there are 1,700 AM stations in the country; of these, 1,300 have applied to migrate to FM.
Source: Government of Brazil