This feature that some radios have seem to have various names:
- band scope
- spectrum scope
- water fall
I understand the first three names, but not panadapter. Where does it come from?
Marcel Wallace founded Panoramic Radio Corp. and details his "Panoramic radio receiving system" in patent US2279151A (1938). Page 2, column 1, line 19 of the patent gives us a clue as to how the physical "panoramic" concept made its way into what we now consider to be a purely electrical phenomenon:
...provide a panoramic radio compass system having visual indicating means operative in correlation to the radio compass system...
In "One-Chip Panoramic Adpapter" Shortwave Magazine for January 1995 pp. 18-25, Bill Wilson makes this attribution:
To the best of my knowledge, the panoramic receiver was invented in the early thirties by a Marcel Wallace ... Dr. Wallace later devised the panoramic adapter which could be connected to a conventional superhet to permit a visual spectrum display, and, along with the Hallicrafters company, coined the term 'Panadapter'.
Figure 4 from Wilson's article shows that the "adapter" picked off its input before the IF signal was filtered by the receiver's high-selectivity stages. Comprising its own RF amp, mixer, oscillator, filter and detector, the panadapter is essentially a second receiver, but one who's output is meant to be displayed visually rather than decoded, audibly or otherwise.
"Panorama, an unobstructed and wide view of an extensive area in all directions."
A "panoramic adapter" for implementing a "wide view" of the radio spectrum is abbreviated as "panadapter".