Fortunately, you don't need thousands of feet of wire to measure a transmitted signal's PSD. You can measure PSD with a spectrum analyzer such as the Agilent Technologies 4395A (which covers the DSL ...

These spectrum analyzers can measure from 1 Hz to 3 GHz (RSA5103A) or 6 GHz (RSA5106A) and offer a much greater dynamic range than an oscilloscope. Both also provide an outstanding noise floor and ...

The Fundamentals Of Spectrum Analysis Understanding Signal Analyzer Architectures Use A Signal Analyzer To Measure Power Supply, Regulator, And Reference Noise This can be achieved, for example ...