APCO 25 9600 baud Digital talkgroups

rescueone · #1 (**permalink**) 12-02-2005, 02:44 PM

I'm monitoring a new APCO 25 9600 baud Digital system in my area. The system is still under construction and only being tested at this time. The only talkgroups that have turned up are 00001 and 01000. Do these look like valid 9600 digital talkgroups? I'm used to the 36 baud systems with the talkgroups in multiples of 16. (34000, 34016, 34032 etc).

mikey60 · #2 (**permalink**) 12-02-2005, 02:54 PM

Yes those are valid talkgroups on a 9600bps P25 system. Any decimal number from 1 to 65535 could be considered valid.

Mike

seamusg · #3 (**permalink**) 12-02-2005, 03:29 PM

What new system are you monitoring?

Joseph11 · #4 (**permalink**) 12-02-2005, 04:08 PM

It's not 36 baud, it's 3600 baud.

N_Jay · #5 (**permalink**) 12-02-2005, 05:49 PM

Quote:

Originally Posted by Joseph11

It's not 36 baud, it's 3600 baud.

And it's not 9600 baud, it's 9600 BPS, 4800 baud.

P.S. The 3600 baud, is also 3600 BPS

Joseph11 · #6 (**permalink**) 12-02-2005, 05:56 PM

You got me. I always confuse those two. Thanks.

seamusg · #7 (**permalink**) 12-02-2005, 08:04 PM

Quote:

Originally Posted by N_Jay

And it's not 9600 baud, it's 9600 BPS, 4800 baud.

P.S. The 3600 baud, is also 3600 BPS

Quote:

Originally Posted by Joseph11

It's not 36 baud, it's 3600 baud.

Why are you guys being nit picking THE ORIGIONAL ORIGIONAL QUESTION WAS ABOUT TG'S ON AN P25 SYTEM!!!!!

Joseph11 · #8 (**permalink**) 12-02-2005, 09:59 PM

Calm down, sorry about that. The original question has been answered.

seamusg · #9 (**permalink**) 12-02-2005, 10:09 PM

Quote:

Originally Posted by Joseph11

Calm down, sorry about that. The original question has been answered.

You cold be nice to the guy. it was only his third post.
I take it MA is not on the east coast?
Covering all of CT, DE, DC, NJ, and RI - plus parts of NY and PA

N_Jay · #10 (**permalink**) 12-02-2005, 10:28 PM

Quote:

Originally Posted by seamusg

Why are you guys being nit picking THE ORIGIONAL ORIGIONAL QUESTION WAS ABOUT TG'S ON AN P25 SYTEM!!!!!

Relax, just having fun.

Joseph11 · #11 (**permalink**) 12-02-2005, 10:36 PM

I was being a nice guy, I corrected his error. I'll add Massachusetts sometime in the future.

Al42 · #12 (**permalink**) 12-02-2005, 10:53 PM

Quote:

Originally Posted by Joseph11

You got me. I always confuse those two.

Most people aren't even aware that bps and baud are different. Of those (relatively) few who are, most don't know which is what. Only those actually in the field usually know what the words really mean.

seamusg · #13 (**permalink**) 12-02-2005, 10:56 PM

Quote:

Originally Posted by N_Jay

Relax, just having fun.

I think you chased the guy away

seamusg · #14 (**permalink**) 12-02-2005, 11:01 PM

Quote:

Originally Posted by Al42

Most people aren't even aware that bps and baud are different. Of those (relatively) few who are, most don't know which is what. Only those actually in the field usually know what the words really mean.

OK I'll bite . how many bits to a binary unit as in BAUD.

N_Jay · #15 (**permalink**) 12-03-2005, 12:35 AM

Quote:

Originally Posted by seamusg

I think you chased the guy away

Couldn't have been ME, cause I did not comment on anything HE said.

I commented on Joseph11's correction. (and he is still here).

N_Jay · #16 (**permalink**) 12-03-2005, 12:38 AM

Quote:

Originally Posted by seamusg

OK I'll bite . how many bits to a binary unit as in BAUD.

Bits is information.

Baud is symbols.

1 bit per baud in a 2 level system. (ie 2 level FSK)
2 bits per baud in a 4 level system (QPSK)

rescueone · #17 (**permalink**) 12-03-2005, 09:33 AM

Hey guys, I didn't get chased away, I was at work till this morning. No offense taken about the correction to my typo (3600 not 36), so with that said, the system I'm watching is the new RI Statewide system.

aka_ramon · #18 (**permalink**) 12-06-2005, 11:34 PM

Since we're being particularly picky in terms of definitions, let's be precise, yes? Baud is not the number of "symbols" but rather it is the number of "symbol state changes per second."

Computer folks know the difference, as well as radio professionals.

As was correctly pointed out previously, in a 4-level phase shift keying system (QPSK), the number of times the phase shifts per second is the BAUD rate. Since each phase shift conveys two bits of information, the effective throughput in bits per second is two times the baud rate: Hence P25 systems at 4800 baud, but at 9600 bps.

Knowing the baud rate really isn't very important, unless you have to deal with the physical properties of the channel... like if you're writing software to decode a P25 CAI data stream: You'd have to know the baud rate to ensure that you sampled the signal often enough to capture the signal transitions.

R