Dear Alan:
--Great post. I enjoyed it very much. We used to use a version of these, called panoramic receivers. Same output you showed except we would have little markers at the bottom showing where our receivers were tuned. Because the radio frequencies looked like blades of grass on our green scopes, tuning to a signal was called mowing the grass. You would just move your little marker to the spike, and viola you could hear the signal. Radio stations and other constant sources would be there all the time. What interested us were the "Push To Talk" spikes. And what was most interesting of course was "Complex Working" where signal A would come up for a few seconds then signal B would come up for a few seconds followed by signal A...and Bobs you uncle. I would venture to say that, even with encipherment and frequency hopping, these things are still proving useful in many cases, to the FCC and probably to some other folks, whom I will not mention here.
"Marconi invented the radio but he had to wait years and years till anything decent was on." Johnny Carson
Best Regards
Clear Ether