POCSAG

Its the way of things. This circuit was solid in 1996, and is now supplanted by software-defined radio.

POCSAG is analog and Flex is digital clear.

For some hacking fun, try

https://en.m.wikipedia.org/wiki/Software-defined_radio to decode

 

https://en.m.wikipedia.org/wiki/POCSAG

More info @ 

https://www.rtl-sdr.com/rtl-sdr-tutorial-pocsag-pager-decoding/

Peace and good morning.