Network Surveying Tools?

I’m a pretty competent home networker who has volunteered to help a friend figure out some persistent networking problems. I think there may be an issue of signal loss due to the positioning of the router, and I want to be able to demonstrate that with data.

Does anyone know of a network surveying tool that would display, at a minimum, signal strength at various sample points? Ideally I’d like to be able to use this on iOS, but I can also use it on MacOS. I’m very comfortable with the command line if there are tools you would suggest using there.

Thanks!