Middlesex County, NJ-USA EDACS system had a few of the base station consoles in the Sheriff's Dept that was transmit-analog, and the mobiles and portables in the field were ProVoice digital when that system was on the air...
When I was creating fleetmaps, and master personality files for customers, I strongly discouraged
the use of mixed format on a single talkgroup.
On an EDACS system, you have 2048 available talkgroups, regardless of A/F/S structure.
If a talkgroup is analog. Keep it that way.
Unencrypted digital. Keep it that way.
Encrypted digital. Keep it that way.
Don't mix formats.
That is why you see systems were one side of a conversation is secure (or unencrypted digital) and the other-side is clear. This is how people accidentally screw-up and discuss something sensitive in the clear and not in secure. (I personally saw Reagan's motorcade have to be rerouted because someone was given the route back to the airport in secure, and repeated it back to his Supervisor in the clear!)
This is called AUTOSELECT
mode, and is a throwback to conventional, were the users/agency only had one conventional frequency or repeater for all of their comm traffic. With AUTOSELECT, if someone calls you (trunked or conventional) in secure mode, and you reply within a predetermined time period, you reply in secure mode. Past that time period, you reply in clear mode. The timing value is your SCAN HANG TIME. The big issue comes in were users have their radios programmed for zero (Ø) hang time.
Back in the edacs and conventional era, clear equaled analog voice. Digital has a 'digital' sound to it. Users could tell the difference. With the advent of P-25 systems, everything is digital, and therefore has the 'digital sound' to it. You cannot tell !!!
This is why I would always program radios for FORCED ON
encryption mode. (Moto called this 'strapped' encryption.)
No chance to screw-up.
My humble 2¢ worth....