First, you need to convert the Month field from alphanumeric string to a number. You can do it in a number of ways. One of them is this:
Match(Month, 'Jan', 'Feb', 'Mar', ..., 'Dec')
Then, use this commonly used calculation of the Quarter:
'Q' & ceil(MonthNumber/3) as Quarter.
www.masterssummit.com - take you QlikView skills to the next level!