I primarily monitor Chicago federal conventional frequencies and have never heard mixed mode used. It's either all Clear/Code analog or all Clear/Code P25, never a mix of the two on a frequency/system.
And... certain Chicago FBI frequencies/systems and DEA (original 6 channels) still use Clear/Code analog.
I've been hearing for over a year now that the St. Louis City P25 system is to go fully encrypted. About a year ago, I did start noticing encrypted radios but the dispatcher would come back in the clear. So I started taking notes of the encrypted radio ID's using a 996XT set manually on a talkgroup. I only did that for a couple months as it was boring. Now a year later, it seems the amount of encryption has not really changed or maybe I'm just not noticing it. I used to monitor that system with a PSR600 but the encryption sounds annoyed me so I settled on using the 996XT as it skipped over them. The drawback was that the GRE did a much better job at decoding the P25 data than the 996XT. I finally put up a 12 element Yagi and that helped the 996 a bunch. If there is more encryption on the system, I'm not noticing as I use the 996 now. The amount of clear traffic seems the same though so who knows. My guess was that they were slowly adding encryption a radio at a time while working towards total system wide encryption. I keep expecting to hear no traffic some day with an in the clear guy every now and then as they get down to the last few radios but it is still the other way around. Much more clear talk than encrypted. I should dig out my list and see if my list still matches what is heard today.
Maybe a budget cut cancelled the encryption plans or perhaps someone figured the benefit of the extra public ears and eyes outweighed the benefits of encryption. That does not really make sense though as most tac and undercover is also still in the clear. I'm thinking maybe the encrypted radios are the ones used by the shift supervisors perhaps. All just a guess really so I guess only time will tell.
Having a mixed system like this does play hell for those with the scanners that will not mute it out or skip over it (encryption that is).
I've heard a few live feeds that were broadcasting similar systems. Those I found very annoying as I could not reach up and hit a resume button! All you can do is mute your audio or stop listening to the feed. If I were into broadcasting live feeds, I don't think I could leave a feed like that up as I know how annoying it can be. I'd go out and get a Uniden or PSR800 instead so the listeners do not have to put up with it. I'm sure it does not bother some people and especially those that do not own or cannot afford a digital scanner. They are probably very happy even when the encrypted radios come on the air. You know what it sounds like, it sounds almost exactly like a Uniden does when getting a poor signal on a simulcast site! When I first heard it, I thought for sure something had failed with my antenna or worse yet, the PSR-600! Then I fired up the 996XT and parked it on one of the TG's that I'd heard the broken speech on and waited until I heard it again from the PSR600's speaker. Sure enough, the 996 display showed the letters ENC in its display. Then I just knew this was the beginning of the end but a year later, it's still about the same.
Go figure.
Good you say "I guess", otherwise you may incriminate yourself.
It was really an old high school buddy that did the "I guess"! He worked at the hospital and was speculating what this new company may have been saying or not saying over the radios. I myself have heard speech inversion use in the area but I do not have the means of decoding it. Back when you could purchase inversion decoders from the back of magazines, I checked and never ever heard any speech inversion in use in this area at all so I never wasted my money on any of them. I seem to recall that they were not very cheap back then. The old Police Call books even reported some of the local muni's as using it here but I guess I was out of their range as I never picked it up. So I did not waste my money on a decoder as there was nothing to decode. It's kinda funny though as now you have all this new technology and only recently did I start hearing yesterday's technology around here! None of it is a strong signal though except for what I assume is still my buddies hospital using it.