How to create a calculated table based on a table with data ranges?

Sorry, I misunderstood the requirement... Here's the correct solution (even though this calculation should be done in Power Query).

// Assuming period is int

[Unpivoted Table] =
SELECTCOLUMNS(
    generate(
        T,
        var __start = T[Start Period]
        var __startDate =
            var __year = int( __start / 100 )
            var __month = mod( __start, 100 )
            var __day = 1
            return
                date( __year, __month, __day )
        var __end = T[End Period]
        var __endDate =
            var __year = int( __end / 100 )
            var __month = mod( __end, 100 )
            var __day = 1
            return
                date( __year, __month, __day )            
        return
            DISTINCT(
                SELECTCOLUMNS(
                    CALENDAR( __startDate, __endDate ),
                    "@Period", int( format( [Date], "yyyyMM" ) )
                )
            )
    ),
    "Id", [Id],
    "Period", [@Period]
)