How is a system both Type II and P25?

[RaleighGuy]

Our local county TRS is a Type II system, the CC is Type II and it is decoded on the scanner and Unitrunker as Type II. But all the voice channels and traffic decode as P25 in DSD+ and Unitrunker, though I still am picking it up as a Type II on the scanner. Several of the radios are also able to operate on the statewide P25 system as well as the Type II county system.

Will someone explain what I'm seeing here and why this is possible?

 

[GTR8000]

It's a Motorola Type II system using the P25 CAI (Common Air Interface). In other words, P25 voice with a 3600 baud control channel, vs a "true P25" 9600 baud control channel. It's actually very common, countless examples of Type II systems with P25 CAI. Most of these systems predate P25 trunking becoming available/common, and so it was a way to get digital talkgroups on the Type II system, by using the IMBE vocoder.

 

[RBMTS]

Wake County? It is a Type II system but also allows for digital traffic. Thus why the system info states:

System Type:	Motorola Type II SmartZone
System Voice:	Analog and APCO-25 Common Air Interface

So Type II systems can be a combination of both analog and digital 3600 baud. Unlike Phase I or II that are digital only.

 

[ecps92]

And, depending on how the system was designed, Not all of the Voice channels maybe allocated to the P25.

Here in MA the old State Police TypeII has some P25 Voice TG's but they have been only observed on 2-3 frequencies per Site.

Some [such as the Federal Bureau of Prisons] allocated all frequencies to use P25 Voice.

It's a Motorola Type II system using the P25 CAI (Common Air Interface). In other words, P25 voice with a 3600 baud control channel, vs a "true P25" 9600 baud control channel. It's actually very common, countless examples of Type II systems with P25 CAI. Most of these systems predate P25 trunking becoming available/common, and so it was a way to get digital talkgroups on the Type II system, by using the IMBE vocoder.

 

[RaleighGuy]

Thank you gentlemen, now I understand.

 

[DJ11DLN]

And, depending on how the system was designed, Not all of the Voice channels maybe allocated to the P25.

Here in MA the old State Police TypeII has some P25 Voice TG's but they have been only observed on 2-3 frequencies per Site.

Some [such as the Federal Bureau of Prisons] allocated all frequencies to use P25 Voice.

This is how our statewide system (Safe-T) was prior to the cutover a couple of years back. There were a few analog TGs in my area right up to the end but most were P25 though it was a Type II Smartzone system. Now it's pure P25...I get a little nostalgic for those analog TGs sometimes even though it seems to work better than the old system did.

 

[GTR8000]

And, depending on how the system was designed, Not all of the Voice channels maybe allocated to the P25.

Here in MA the old State Police TypeII has some P25 Voice TG's but they have been only observed on 2-3 frequencies per Site.

Some [such as the Federal Bureau of Prisons] allocated all frequencies to use P25 Voice.

Cost saving measure, as it would require adding the P25 CAI to some of the repeaters at each site or subsite, vs all of them. The digital talkgroups are steered towards those traffic channels, while the analog talkgroups are setup to prefer the remainder of the repeaters, but can obviously use the ones with the P25 CAI if necessary.