How to truncate a row of multiple words

Originally Posted by Potholes

As an exercise I am trying something out so as to learn more about Excel.

Not the best way to start trying to learn!

As Ali has pointed out, you will need a set of rules to work with, each of which must be clearly defined and exact. Excel can not identify similarities in the same way that a person can.
For example, you can look at (430 - 450 Mhz) and 12-14 Mhz and see both as frequency ranges, excel will only see them as numbers and letters. A common rule to identify both ranges as the same could also identify 10525 MHz X band; 24150 MHz as a match, which based on your sample would be incorrect.

Every time you add a new phrase you will need to assign rules to that phrase and check that none of the existing rules conflict.

Teaching a goldfish to play the guitar would be an easier task.