I'm kind of curious if there's any activity around modifying older radios. I have a couple of HTX-202's that I'm eyeing for some work one day. My favorite one is actually the first Ham Radio I ever owned, it was new in box from Radio Shack circa 1993/1994. Probably 1994, but I'm not sure how long I had it before I officially had my ticket. The other one is a Hamvention special some guy in the flea market was apparently desperate to get rid of.
My original is exhibiting the ER-1 code, for a dead/dying memory backup battery. The Hamvention one has some weird squelch problem where it won't always open squelch when it receives a signal. It also had ER-2 when I first turned it on, but that was easily cleared. It also is in seriously bad need of being disassembled so I can spit and polish the case some. This Hamvention 202 was really beat up in it's former life.
According to the service manual, these radios are split up into two main PCBs, an RF board and a CPU board. I wonder if I can figure out how to control the RF board with a homebrew CPU board. Then flash, or some other non-volatile memory could be used to store the programming. Other features could be added as well. DCS maybe?
I remember finding a page about EF Johnson radios for 900mhz where someone made an external control system for one that made it frequency agile. Of course, now that I want to link to it, it's nowhere to be found.
Here are a couple of relevant links but talking about FRS radios: