So you can build a high gain AF amp and a RF probe and be in business. The probe would be like this one.
Now how would you use it?
If you started at the first RF amp input and had signal and moved to its output you would expect to hear a louder signal. As you progress through you would be turning the volume down to a good listening level and expecting and increase. When you step over a stage and the signal drops you have found the problem area. Then you troubleshoot that stage......
So build an amp and probe and you are set to troubleshoot radios.