Tonight I was poking around the electronics station, learning where everything is.
I saw a spectrum analyzer ( VHS Equipment Review: HP8591A 9khz - 1.8Ghz Spectrum Analyser, Keep for VHS ). It’s one of those tools I always wish I had (or even access to).
It had a thin layer of sawdust over the screen, I vacuumed and brushed it in the workshop.
Turned it on, seems to work. I had a 900 MHz ISM device nearby (LoRa Meshtastic) and was able to trigger blips on the spectrum. Not qualified to test it more thoroughly than that.
Once I get wiki edit access, I can document it, as requested in the original topic.