Before revision: A spectrum scope is normally a lot cheaper than a spectrum analyzer, because the aim is not high quality frequency resolution - nor high quality signal strength measurements.
After revision: Panoramic radio receiving system US 2279151 APanadaptors Quote: "...The panoramic spectrum display, invented by Marcel Wallace in the 1930's, provides a radio operator with a graphic display of radio signal amplitudes at frequencies close to the signal to which his radio is currently tuned..."A spectrum scope is normally a lot cheaper than a spectrum analyzer, because the aim is not high quality frequency resolution - nor high quality signal strength measurements.