Batboard

We are getting a new P25 Trunking system. The county is buying the Kenwood P25 radios with the trunking option installed.

My first question is what type of P25 is kenwood using and what Motorola digital would be compatible?
Second what type of trunking is their option board doing and what Motorola would be compatible with that?

Thanks in advance, w4ekg

Not sure just what your asking here. The P25 is an open standard so that all radios that
are P25 capable can operate on any P25 trunking system. P25 is a digital only system.

The rub comes with some systems not being a true P25 compliant system. They also
throw in for good measure some proprietary functions that only the system designed
radios will do. As time goes on, these special functions are going by the roadside.

If you want to look at it from the customers point of view, there are now a number
of companies that have a true P25 trunking radio on the street. As you well know
Motorola and Kenwood have them. Also there is some E.F. Johnson, Icom, MA-COM,
Daniels and others that have made the jump into the frenzy. When an agency is
now looking to buy new P25 trunking radios, there is competition building to force
the prices down. It is no longer a one way street with only mother Motorola
able to demand what ever blood money they can extract.

To go back to your original question, you have to be careful today when people
talk about a P25 trunking system. Unless the data rate on the control channel
is at the 9600 baud rate it is not a true P25 system. The older 3600 baud rate
control channels are not P25. They are what is called P16. These systems are
a mix of analog and digital operation. Sort of the first steps into trunking. You
could have some mixed systems today, but they don't work well. The migration
to the 9600 data rate is slowly being phased in.

As with everything that Motorola does, they are jacking up the cost of maintaining
the older trunking systems. In a drastic move to speed the migration, support
for some of the older systems and software has been shut off. It's the old adage
of shortening the life cycle to make customers purchase new equipment. What
this has done is open sores in customer's attitudes and allow outside competition
to walk in with other company radios.

Jim

CPD534 wrote:We are getting a new P25 Trunking system. The county is buying the Kenwood P25 radios with the trunking option installed.

My first question is what type of P25 is kenwood using and what Motorola digital would be compatible?
Second what type of trunking is their option board doing and what Motorola would be compatible with that?

Thanks in advance, w4ekg

Jim202 wrote:Unless the data rate on the control channel
is at the 9600 baud rate it is not a true P25 system.

Please do not continue to propagate this error. The data rate on an APCO-25 CAI channel, be it control or voice, is 4800 BAUD. If you doubt me, get the APCO spec and look it up.

Yes, the data rate is 9600 bits per second, but that is because APCO-25 CAI transmits 2 bits per symbol.

But it transmits 4800 symbols per second - that is the DEFINITION OF BAUD.

Wowbagger wrote:

Jim202 wrote:Unless the data rate on the control channel
is at the 9600 baud rate it is not a true P25 system.

Please do not continue to propagate this error. The data rate on an APCO-25 CAI channel, be it control or voice, is 4800 BAUD. If you doubt me, get the APCO spec and look it up.

Thank you for your pedantry. Saved me from having to do it.

tvsjr wrote:Thank you for your pedantry. Saved me from having to do it.

Y'know, I'm just about *this* close to taking the relevant section of the TIA document - just that paragraph - and posting it here under "fair use", just to deal with the folks who say "Duuuh but da Motorola salesguy calleded it 9600 baud".

Some folks here may not realize that I *have* the TIA spec on my desk at work, and refer to it frequently.

i would like to see that made a sticky as well....

"we dun gots us a 9600 baud scanner..."

ugh

OK, I'll see if I can get into the documentation system at work tomorrow and get that paragraph as text, and put it here along with the full attribution.

Failing that I'll scan that page, crop it, and post it.

One paragraph should fall under Fair Use according to the Copyright Act.

OK, to put this to bed:

First, from the U.S. Institute for Telecommunication Sciences definition of baud:

U.S. Institute for Telecommunication Sciences wrote: baud (Bd): 1. A unit of modulation rate. Note: One baud corresponds to a rate of one unit interval per second, where the modulation rate is expressed as the reciprocal of the duration in seconds of the shortest unit interval. 2. A unit of signaling speed equal to the number of discrete signal conditions, variations, or events per second. (188) Note 1: If the duration of the unit interval is 20 milliseconds, the signaling speed is 50 bauds. If the signal transmitted during each unit interval can take on any one of n discrete states, the bit rate is equal to the rate in bauds times log2n . The technique used to encode the allowable signal states may be any combination of amplitude, frequency, or phase modulation, but it cannot use a further time-division multiplexing technique to subdivide the unit intervals into multiple subintervals. In some signaling systems, non-information-carrying signals may be inserted to facilitate synchronization; e.g., in certain forms of binary modulation coding, there is a forced inversion of the signal state at the center of the bit interval. In these cases, the synchronization signals are included in the calculation of the rate in bauds but not in the computation of bit rate. Note 2: Baud is sometimes used as a synonym for bit-per-second . This usage is deprecated.

(emphasis mine)

Now, from TIA-102.BAAA-A, Project 25 FDMA Common Air Interface:

TIA-102.BAAA-A, page 41 wrote: Section 9: Modulation
9.2 Symbols
The modulation sends 4800 symbols/sec with each symbol conveying 2 bits of information.

(again, emphasis mine).

You can legitimately call APCO-25 a 9600 bit per second protocol, a 4800 baud protocol, but it is NOT a 9600 baud protocol.

Yes Sir!
Seriously though, I do appreciate the follow up with the service document.

Even with a computer background, I used to get that all mixed up... Thanks for the clarification...

But back to the subject if I may, as it is actually very relevant to my situation here. I'm currently writing up a proposal to our powers-that-be for more interoperability for our unit. We provide some fairly specialized emergency services over a very wide area (no, not whackers, actually a government dept...) and we've been asked to ensure we can talk to everyone. My current issue is that one of them is a VHF P25 Trunking system. We have the appropriate authority to 'join' it, but we're to procure and manage our own equipment. The roll-out is all MA-COM, but we'd prefer a Ma M solution to keep the types of radios in our truck to a minimum (affects training, etc.). Anyone had any issues with 'true P25' from other vendors and Ma M radios?