Adding/Changing CTCSS in Military Radios

[Wire Fox]

I realize this is a very optimistic request, but with the practical benefit it might serve me in the future, it seemed worth asking...

I haven't divulged too much into the design of a CTCSS circuit, but I'm curious as to what it takes to actually add CTCSS into a radio...or in the case of "newer" military radios, how to make use of more tones other than 150.0Hz. In the amateur radio world, there are kits and commercially available add-in PCBs intended to insert CTCSS into the output of very old VHF radios...these usually simply provide a 3.5mm jack that remains connected to an external tone generator, such as a cell phone, computer, or discreet hardware device. All of the how-tos I came across were very specific to a certain radio "solder the red wire to pin #xyz", but didn't describe what was actually being connected to what circuit so that I could understand exactly what they did.

Considering much newer radios that are software-controlled and sometime software-defined, I have to wonder if there's any simple way to control the built-in CTCSS to have it transmit a tone of my choosing... A specific case would be my PRC-138. I haven't found anything in the documentation for it, so I have to assume that it's not a finely controllable option.

Anybody have any ideas on how to accomplish adding improved CTCSS to enable interaction with most amateur repeaters?

 

[papakb]

In most of the military radios like the VRC-12 series you would have to change the tone generator and then the 150Hz filter that I think is down in the discriminator to receive the new tone. And even after doing that you could talk to civy rigs but not other military radios unless they were similarly modified.