WMATA P25 Talkgroups

[tvengr]

According to the 2 new talkgroups in the database for the WMATA P25 system, you can calculate the remainder of the TGID's for P25 talkgroups by looking at the P16 talkgroups and dividing the TGID's by 16.

 

[tvengr]

This morning, I am receiving Branch Avenue 1 (TGID 2175) which supports the divide by 16 scenario in my previous post. I have seen a number of Motorola Type II systems follow that plan when they transition to P25. Surprisingly, I am able to receive the WMATA P25 system from my location in northern Baltimore County.

 

[tvengr]

I am receiving Shady Grove 1 on TGID 2151 which also supports the divide by 16 scenario.

 

[jtwalker]

Is there a reason behind the “divide by 16” logic?

 

[tvengr]

Is there a reason behind the “divide by 16” logic?

All Motorola Type II systems must have a TGID spacing of 16 or multiples of 16, beginning with 16. There are status bits for each talkgroup. For TGID 16, TGID's 17 through 31 control certain functions. For instance, TGID 16 is the normal talkgroup, TGID 17 is all talkgroups, and TGID 18 is emergency. Since the Motorola normal TGID's are spaced by 16, you can keep the P16 talkgroup names and divide the P16 TGID's by 16 and the P25 TGID's will appear sequentially. For example, P16 TGID's 16, 32, and 48 become P25 TGID's 1, 2, and 3. Since most of the P16 TGID's on the WMATA system are spaced by 32, the converted numbers will be every other odd number:

WMATA P16
34416 Shady Grove 1
34448 Shady Grove 2

WMATA P25
2151 Shady Grove 1
2153 Shady Grove 2

It is very easy to convert the P16 TGID's to P25 TGID's by dividing by 16. That is why it is often done when a P16 system transitions to a P25 system. That is why you will see every other TGID on many systems. This is all speculation based upon prior experience. I have no inside information on how it will be done.

Status Bits​

​

Dec ID + #	Usage
ID+0	Normal Talkgroup
ID+1	All Talkgroup
ID+2	Emergency
ID+3	Talkgroup patch to another
ID+4	Emergency Patch
ID+5	Emergency multi-group
ID+6	Not assigned
ID+7	Multi-select (initiated by dispatcher)
ID+8	DES Encryption talkgroup
ID+9	DES All Talkgroup
ID+10	DES Emergency
ID+11	DES Talkgroup patch
ID+12	DES Emergency Patch
ID+13	DES Emergency multi-group
ID+14	Not assigned
ID+15	Multi-select DES TG

 

[jtwalker]

All Motorola Type II systems must have a TGID spacing of 16 or multiples of 16, beginning with 16. There are status bits for each talkgroup. For TGID 16, TGID's 17 through 31 control certain functions. For instance, TGID 16 is the normal talkgroup, TGID 17 is all talkgroups, and TGID 18 is emergency. Since the Motorola normal TGID's are spaced by 16, you can keep the P16 talkgroup names and divide the P16 TGID's by 16 and the P25 TGID's will appear sequentially. For example, P16 TGID's 16, 32, and 48 become P25 TGID's 1, 2, and 3. Since most of the P16 TGID's on the WMATA system are spaced by 32, the converted numbers will be every other odd number:

WMATA P16
34416 Shady Grove 1
34448 Shady Grove 2

WMATA P25
2151 Shady Grove 1
2153 Shady Grove 2

It is very easy to convert the P16 TGID's to P25 TGID's by dividing by 16. That is why it is often done when a P16 system transitions to a P25 system. That is why you will see every other TGID on many systems. This is all speculation based upon prior experience. I have no inside information on how it will be done.

Status Bits​

​

Dec ID + #	Usage
ID+0	Normal Talkgroup
ID+1	All Talkgroup
ID+2	Emergency
ID+3	Talkgroup patch to another
ID+4	Emergency Patch
ID+5	Emergency multi-group
ID+6	Not assigned
ID+7	Multi-select (initiated by dispatcher)
ID+8	DES Encryption talkgroup
ID+9	DES All Talkgroup
ID+10	DES Emergency
ID+11	DES Talkgroup patch
ID+12	DES Emergency Patch
ID+13	DES Emergency multi-group
ID+14	Not assigned
ID+15	Multi-select DES TG

Thank you for the education.

 

[tvengr]

So far, all of the new just listed WMATA talkgroup ID's follow the P16 TGID divide by 16 for P25 TGID rule.

 

[N4VKF]

So far, all of the new just listed WMATA talkgroup ID's follow the P16 TGID divide by 16 for P25 TGID rule.

Yep I just reported what I caught while I was in NOVA for a bit.