[ScanIndiana] RE: Indianapolis Fire Dept. Questions

[David L Norris]

> What do you mean patched?

Good question...  I'll post the answer to the group (names removed :-)
since I'm sure others may want to know.

By patch I mean: to temporarily connect multiple talkgroups together as
if they were a single talkgroup.


To go into some depth (for those who may care to know):

Control operators can patch multiple talkgroups so everyone on all of
the patched talkgroups can communicate with each other.  For example, if
the control operator patches 115 (112 + 3) to 5171 (5168 + 3) then
everyone formerly on 5168 and 112 can talk to each other as if they were
on the same talkgroup.  A 115-to-5171 patch is fairly common when there
is a car chase from IPD-West into County-West, for example.  On 112 you
might hear control say "I'm patching to CountyWide" and 112 goes dead
until after the chase ends.

TrunkTrackers don't fully support patches and just latch on to the first
talkgroup added to a patch.  A TrunkTracker might refer to the
115-to-5171 patch as "talkgroup" 115.  If 5171 is patched to 115 then
the TrunkTracker may refer to it as 5171 rather than 115.  So, to hear
all traffic on a patch between 5171 and 115 you may need to scan _both_
5171 and 115.  Tricky isn't it?  Which one it is depends largely on the
order the control operator pushes the buttons on the console.  During a
given incident (i.e. car chase) it may flip-flop several times or go
somewhere else entirely.


Also, beware that if you are scanning only talkgroup 112 then the older
Uniden TrunkTrackers will go silent whenever that talkgroup changes
status (i.e. car chase, officer emergency, broadcast, etc).  To catch
all the traffic on 112 you may need to monitor 112, 114, 115, 119 on
older Trunktrackers.  Refer to your scanner's manual if you aren't sure
how it operates in this regard.  (There are also tricks to make older
TrunkTrackers treat 112, 113...127 as a single talkgroup.)


What a TrunkTracker calls talkgroup 3283 is really talkgroup
(hexadecimal) CD3 in status 3 (0xCD33) to the Motorola radios.

Common talkgroup status used by MECA (112 is just an example):
112 = 112 (+0) normal status
114 = 112 (+2) radio(s) in emergency status
115 = 112 (+3) patched to one or more talkgroups
119 = 112 (+7) multiselect (one-way broadcast to many talkgroups)

120 = 112 (+0 +8) with normal encrypted traffic
...


I've written some programs to make sense of TrunkTracker talkgroups:
  http://webaugur.com/wares/trunkid.html

Lots of information here about how trunking systems work:
http://www.radioreference.com/modules.php?name=Content&pa=showpage&pid=1

MECA operates several Type-II Simulcast systems covering all of Marion
and (by summer 2004 most of) Hendricks County.  Statewide SAFE-T system
is several (currently two?) ASTRO-25 SmartZone (Omnilink?) systems with
(eventually) over 150 sites.

-- 
 David Norris
  http://www.webaugur.com/dave/
  ICQ - 412039