by Dave Rishavy & Tomas Berghall:
The one piece of gear that’s essential for EMC troubleshooting is a spectrum analyzer. You can buy a decent portable for about $10k or used ones go for $1k to $5k if you don’t mind the 30 to 80 pounds of weight or the initial investment. This article reviews several models that cost under $2,000.
Compare low-cost spectrum analyzers - [Link]