Hi Dave,
I’m not sure what your project is but you may want to look at a variable RF signal samplers like a Bird 4275. There are also less expensive units that have sliding plungers (eBay). Here is a video showing the use of a Signal Hound SA44B with RF sampler (video is about setting modulation level in a packet TNC). Not sure if this video applies to what you want to do but it may give some ideas.
https://www.youtube.com/watch?v=xIqGWz89mWk
Hank