How little you realize! This has been done for over 50 years, with predetection recording. When I was but a young and adventurous RF Explorer I built just such a Rube Goldberg device in the late 1960’s. I became aware that video recorders put out signals in the 80 meter ham band. Realizing that when I played back a taped prerecorded session it caused the same signals to be present at the same exact frequencies I studied the service manual for the video recorder that I was working on. Upon studying them very closely that these video signals were in the 3 to 4 megacycle (now called MegaHertz) range both on record and playback. I then tried first hooking an antenna into the video input ( with very little but noticeable results!) I then added an Ameco tunable recieve preamp in line between the antenna and the BNC video input. After tuning it to the 80 meter range I recorded and then played it back listening with my old National NC109 reciever. Over and over I heard the same signals. I did a deeper dive into the service manual and found points closer to the record and playback heads that served my purpose better. I soon acquired a similar recorder from a local cable tv station that they were nolonger using due to upgrade. I got the required service manual on that unit after confirming that it functioned the same as the first unit had, I proceeded to modify it to my purposes. I found the best point to apply my preamped antenna input signals, then found the cleanest strongest output signals from the tape head and fed them to new BNC connectors mounted on the rear of the unit. I then realized that I needed a way around the tuned input. I found some preamps made by HP at a Radio. Swapmeet. No one much at that time knew what good they were, so they were cheap for a while. Once it was discovered that were for use in the input section of extremely expensive HP Frequency counter that covered up above 1000 Megacycles, not only were they literally Gold but Gold in the eyes of experimenters because 2 meters was all the rage and 450 was coming on, so everybody but everybody wanted preamps to improve their receiving equipment. This drove the price high on these items (as it is still today, when they are available. ). These are wideband preamps, VERY wide band, covering way more than the recorder was capable of, I even used these on the 6 meter band, but I digress. Meanwhile back at the ranch, I built an addition to my setup by enclosing one of these HP preamps in a metal RF sealed enclosure and putting the wideband preamp in place of the frequency tuned one. Now I could run my recorder come back later and play it back and tune up and down the bands with my reciever and listen to various signals on various frequencies over and over. I discovered that on the bottom end my limit was my receivers capabilities which was around 500 Kilocycles. The top end was a little over 10 Megacycles. The receiver was hot enough here, I knew that from frequently listening to traffic in the 11 Megacycle range. But the recorder or the playback section was almost nonfunctional above 10 Megacycles. Sure I could hear WWV and the Strongest of stations on 11.175 Mhz but not much else up there. However down at 2.5, & 5.0 WWV was excellent, conditions permitting. 160, 80, 40 Meters were really functional. I added an old Pan-Adapter that came from an old WWII Radar and Surveillance set up so that I could see either side of the frequency that I was tuned to. This all predated Spectrum Analyzers as we know them today, and long before that I could afford one. With my setup I could record when I had to leave, then when I got back, rewind tune to the desired frequency and listen. Once I heard something of interest (i.e. an interfering signal) I could then tune WWV and know the exact time of the incident. That is the way that the FCC finds offending signals. A report is made of interference on a certain frequency, they pull up the time frame in question, go to the frequency in question and document the interference as evidence of the occurrence. This is the way predetection recording works in principle, while there have been enormous advances in technology, the premise remains the same today. The FCC has shuttered many of their field offices, and the monitoring stations are all but unmanned. Routine maintenance and other scheduled events are still manned but most of the time they are simply remote stations for antennas and remotely operated SDRs. Those stations are mostly remotely monitored by other machines recording wide swaths of frequencies that can be pulled back up and investigated at any future time. Those records are stored in a giant server farm somewhere for those who need access to have at their disposal at some future time. Laurin WB4IVG