All India Radio started with Amplitude Modulation (AM) transmission initially in Medium Wave and shortly followed by Short Wave. Since 1990s, when the Frequency Modulation (FM) technology became common in the field of public broadcasting, various Akashvani centres opened their FM transmission as well. After Delhi, Kolkata started transmission in FM. Presently it has mainly two FM stations - FM Gold (101.1 Mega Hertz) and FM Rainbow (107.0 Mega Hertz). Apart from these, certain other Relay centres are also transmitted in FM.