You can run your RF tests on-site if the system you're developing isn't in your lab, or doesn't fit in your lab, or in an anechoic chamber, for that matter. Your manufacturing technicians can just as readily use it in post-production sample testing. Little special test expertise is required. In the past, one way around the ambient hash and noise problem was to perform your compliance or RFI tests in a remote area, or inside an expensive, and oftentimes large, shielded anechoic chamber or screen room. You can run accurate RF emission tests, even in the presence of annoying ambient signals in the spectrum of interest.
Ambient cancellation is the secret.
In fact, you can now make measurements at test sites that have been proven to be overrun with ambient signals. That means in-place testing can even be performed on the factory floor, for example, or in other previously unsuitable locations. The box's high-speed DSP then cancels interfering ambient signals, while accurately estimating EUT signal strengths. Moreover, the system relates radiating signals to their sources. That's pretty neat.