Given it was an existing receiver they had handy when they did this study in 1981 I'm guessing it's a pretty old bit of kit
https://link.springer.com/content/pdf/10.3758/BF03207940.pdfIn the world of environmental telemetry (this thing was medical) things have moved on quite a bit. With the proliferation of cellular services there is a plethora of equipment that goes straight to the internet with a built in cellular or NB-IoT modem.
There are of course radio based systems still, with common technologies being spread spectrum UHF and LoRa WAN
In the last few years low cost satellite telemetry has become increasingly common. It's arguably more economical for me to measure and telemeter non-intensive measurements (eg daily water level) via satellite than mucking around with cellular, even in urban environments using providers such as Myriota. I can basically deploy a little battery powered device that will measure and telemeter it's results over multiple years for naff-all money.
I'd be surprised if this boat anchor on ebay was still "current" although I don't work in the bio/medical telemetry field.