Flex

Flex is a paging technology from Motorola. Flex has a number of advantages over the older technology based on POCSAG. The most significant are a significantly longer battery life and an improved message integrity because of the Flex protocol's error-correction capability.

Flex can transmit information at three different speeds: 1,600, 3,200 or 6,400 bit/s. Flex pagers can operate on any of the three speeds. They automatically detect the correct speed based on information from the paging signal. Flex uses Frequency Shift Keying (FSK) to transmit the information. 2-level frequency-shift keying (2-FSK) modulation is used for the slowest transmission. The 6,400 bit/s transmission uses 4-level FSK (4-FSK). The 3,200 bit/s transmission may be transmitted at either 2-level or 4-level FSK.

Flex transmission are divided in frames. There are 128 frames in every four minutes. Each pager is assigned to one (or several) frame(s). The pager only have to look at these frames for messages. This gives the opportunity to turn the receveir of in the time between these frames to extend the battery life.

Each frame starts with a synchronization field followed by 11 blocks for information.

Flex can operate in several frequency bands in the VHF or UHF.