Group repetition interval (GRI) indicates the interval of elapsed time from the point when the master station in a chain starts to transmit a pulse group to the point when it starts to transmit again.

In addition, it is also used to designate a specific chain that the receiver will select, and is utilized as the continuous time unit of 10 μs for the GRI that is designated with a 4-digit number between 4,000 and 9,999 and master pulse group transmission.

In order to prevent receiving master station and secondary station signals simultaneously, the minimum GRI needs to be set at an adequate length of time so that it includes time for pulse group transmission from each station’s pulse time (10,000 μs for a master station and 8,000 μs for a secondary station) between each pulse group.

Therefore, the minimum GRI has a direct relationship with the number of overseas stations within the group and the distance between the stations.

In conclusion, GRI needs to be set in such a way that adjacent chains do not interfere with each other and must accurately start at the moment when the first pulse of the master station group starts.

For example, the GRI 9930 Chain repeats every 99,300 μs of the master pulse group as in the picture below.