When using MMDS for broadcasting the signal of the main station to the cable subnets there is a problem of unauthorized viewing of television channels, because they can be received from the air, bypassing the cable network.
    MMDS channels protection by the means of coding them at the transmitting station is connected with their decoding either by the subscriber decoder, which is set at the input of the television receiver or by the group decoder, which is set between the output of the receiving converter MMDS and cable subnet input.
    In the first case usage of the "CryptOn" system in MMDS is carried out similarly as in cable networks of collective television reception.
    In the second case it is necessary to use coders model COD502, 503, 505, 506 to code the channels. The distinctive feature of this coder is the possibility of synchronization by the common sync signal of the transmitter (CST) (Figure 1). The coder, programmed to work in Master mode, creates CST.
    Group decoder differs from the subscriber's one with the availability of the built-in tuner. It helps to receive TV channel with control video data, created by the Master coder.

Figure 1. Connection of coders to the equipment of the main MMDS station.