You can't declare that the frequency fits within a range. If it somehow went outside that range then you would want something to happen right? Like maybe print out an error message or take some other corrective action?
If you declared this limit then how do you tell it what to do outside the range? It can't just stop your whole program and wait until it's fixed - the program is stopped so it can't fix anything.
YOU have to write the code to take an action if the number is outside your desired range. If it's a number typed in by a person, you might print an error message like "Frequency cannot be greater than 11500, please re-enter the frequency..." If it's something coming from another input, then you have to write code to allow for that input giving you an unexpected number.