Stop Pirates? Make 'em legal.
Canada figured this out decades ago. Make it easy and practical to licence legal non-commercial stations and pirate activity drops to near zero.
If you licence them they need to do the engineering study to show that they won't interfere with other broadcasters. Problem solved.
Several years back Canada took things a step further with "Developmental" radio licences. Fill in a ten page form, provide an engineering brief to support the channel that you want to broadcast on, and you get a 5 watt unrestricted licence for three years.
If at the end of three years you're still on the air, you can apply for a full power licence. Easy and legal.