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understanding p25 trunk system information in database

kabriel

Newbie
Joined
Sep 8, 2019
Messages
2
Location
Indianapolis, Indiana
Hi,

Totally new to programming radios. Someone gave me a BCD996P2. I'm in the Indianapolis, IN area. I've read through various references and forum questions on this website, and have managed to install FreeScan and program some easy AM channels (e.g. Indy Airport communications, and CB frequencies).

I am now trying to program the public safety system. I managed to add a P25 standard system. I added a site with the trunk frequencies from site 001 here . I added the red first, and then the 3 blue ones. I also added a TGID group with TGIDs 1 (dispatch), 2 (car-to-car), and 3 (special), but I think this is wrong. Anyway, it does scan through IDs and picks stuff up. I have two questions.

1) Should I add the blue frequencies from the database, or even the gray ones, or just ignore that? Do I need to add a "APCO band plan" frequency?
2) Is the TGID actually the "DEC" code in the talk group sections of the database?

Thanks!
 

hiegtx

Mentor
Premium Subscriber
Joined
May 8, 2004
Messages
6,265
Location
Dallas, TX
Hi,

Totally new to programming radios. Someone gave me a BCD996P2. I'm in the Indianapolis, IN area. I've read through various references and forum questions on this website, and have managed to install FreeScan and program some easy AM channels (e.g. Indy Airport communications, and CB frequencies).

I am now trying to program the public safety system. I managed to add a P25 standard system. I added a site with the trunk frequencies from site 001 here . I added the red first, and then the 3 blue ones. I also added a TGID group with TGIDs 1 (dispatch), 2 (car-to-car), and 3 (special), but I think this is wrong. Anyway, it does scan through IDs and picks stuff up. I have two questions.

1) Should I add the blue frequencies from the database, or even the gray ones, or just ignore that? Do I need to add a "APCO band plan" frequency?
2) Is the TGID actually the "DEC" code in the talk group sections of the database?

Thanks!
Hi kabriel
Welcome to RadioReference

1) Should I add the blue frequencies from the database, or even the gray ones, or just ignore that? Do I need to add a "APCO band plan" frequency?
The frequency that is showing the red color is the primary control channel. The blue ones are alternate control channels. Your 996P2 only needs the control channels to track the system correctly. Normally, that would the frequency in red. However, if, for whatever reason, the transmitter for that frequencies is out of service, then one of the alternates, the 'blue' ones, would be used instead. The gray ones are voice channels, and are not normally needed for the scanner to track the system. While it does not hurt to have all of the site frequencies, they are not needed for a Motorola system, which is the most common. I would note that for systems manufactured by Harris, another company that sells trunked systems, you need to enter all of the frequencies, because their system may use any of the site frequencies as the control channel, and often they rotate regularly.

You do not need to enter a band plan. The scanner receives that data from the control channel. FreeSCAN usually tells you the 'band plan' is missing the first time or two you load the system to the scanner, and occasionally after you've made major changes.. You don't need it, so ignore the warning and after a few downloads to the scanner, it will go away.

FreeSCAN will also warn you at times about missing WX (weather) information. You can ignore that one as well.

2) Is the TGID actually the "DEC" code in the talk group sections of the database?
Yes, the DEC column is the talkgroup ID (TGID) that you need to program.

For more information on trunked systems, see this Wiki article: Trunking Basics - The RadioReference Wiki

If you have not already done so, also look at this page: Program your DMA Scanner - The RadioReference Wiki

You may have already seen this page: Easier to Read BCD996P2/XT Digital Scanner Manual

And, if you did not already know, there is a User Guide in the Wiki for FreeSCAN.
FreeScan User Guide - The RadioReference Wiki
 

tvengr

Member
Joined
Feb 10, 2019
Messages
497
Location
Monkton, MD
The red frequency is the control channel. The blue frequencies are alternates which may be used as the control channel if there is a problem. The red and blue frequencies (control channel and alternates) are the only frequencies you need to enter. All of the frequency information is transmitted on the control channel. You do not need a custom band plan. Standard is fine. Scanners usually use the Dec TGID. Some can be programmed to use either Dec or Hex.
 
Joined
Apr 18, 2009
Messages
1,864
Location
CT
it does scan through IDs and picks stuff up
Check your display while it's scanning. It should say "ID Scan". This means it is scanning only the TGID's you have entered.

If it says "ID Search", it is searching all TGID's. To revert to "ID Scan" mode, press in the silver knob and press "Scan/Search".
 
Joined
Jun 16, 2013
Messages
3,336
Location
Texas
You do not need to enter a band plan. The scanner receives that data from the control channel.
Careful, not all P25 systems are what are called explicit (where they advertise the band plan). 90% are...but there is always that 10% that are not. You see it more commonly with older, small GE/Ma-Com (pre-Harris). There are also a handful of Motorola Type I and Type II systems still out there which are also implicit. If you ever run across one and a standard band plan does not fit, the only way to figure it out is to log the channel messages and work backwards from the licensing database (if available).
 

GTR8000

Well Known Member
Database Admin
Joined
Oct 4, 2007
Messages
7,454
Location
BEE00
Careful, not all P25 systems are what are called explicit (where they advertise the band plan). 90% are...but there is always that 10% that are not. You see it more commonly with older, small GE/Ma-Com (pre-Harris). There are also a handful of Motorola Type I and Type II systems still out there which are also implicit. If you ever run across one and a standard band plan does not fit, the only way to figure it out is to log the channel messages and work backwards from the licensing database (if available).
You're confusing the terms Implicit and Explicit.

Implicit systems always broadcast the band plan, as that is how the subscribers know how to calculate the traffic channels (in conjunction with the Channel ID table in the codeplug). Further, an implicit system broadcasts single-block TSBK messages per traffic channel grant, as the subscribers don't need to be explicitly told what the inbound/outbound frequencies are.

Explicit systems also broadcast a band plan, however they also broadcast explicit instructions using multi-block TSBK messages per traffic channel grant, providing the subscribers with the actual inbound/outbound channel frequencies independent of the band plan. Explicit messaging is found primarily on VHF (and some UHF) systems, since no standard repeater offset plan exists.
 
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slicerwizard

Member
Joined
Sep 19, 2002
Messages
5,455
Location
Toronto, Ontario
^^^ What he said. ^^^

Implicit: GRP_V_CH_GRANT PRI4 TG=104 RID=110008 ch=413.4875-1

Explicit: GRP_V_CH_GRANT PRI4 TG=78 RID=7211026 TXch=158.8275-2 RXch=154.815-2
 
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