[ScanIndiana] Re: New SAFE-T sites in Indianapolis, Newport, Greencastle, Terre Haute

[David L Norris]

On Tue, 2003-08-12 at 21:57, Kyle Thomas wrote: 
> Does anyone know a good website that explains how this SAFE-T system works
> and how to monitor the system.

I don't know of any websites specific to SAFE-T but that would be nice.


Here's an overview. (I really think it needs some diagrams to make much
sense.)

SAFE-T is a Motorola ASTRO-25 Networked system.  The most important
difference with SAFE-T is that it's networked.  This means that
talkgroups can span multiple tower sites.  A talkgroup might exist on
any combination of towers across the state.


Let's say that Officer A in Indianapolis wants to talk to Officer B in
Terre Haute on a statewide mutual aid talkgroup.

When Officer A selects the SW-MA1 talkgroup (statewide mutual aid 1) his
radio contacts the nearest tower (e.g. ISP-52, cell 1) and requests an
affiliation with the SW-MA1 talkgroup.  At that point radio traffic over
SW-MA1 can be trunktracked _only_ on the Indianapolis' trunked system.

When Officer B selects the SW-MA1 talkgroup his radio contacts the
nearest tower (e.g. Terre Haute, cell 8) and requests an affiliation
with the SW-MA1 talkgroup.  Now, radio traffic over SW-MA1 can be
trunktracked on both the Terre Haute _and_ Indianapolis towers.

What does that mean to scanner listeners?  Simple, only trunktrackers in
Terre Haute and Indianapolis trunktracking cell 8 and cell 1
respectively can receive this conversation on SW-MA1.  From a scanning
perspective this is really no different than any other trunked system. 
>From a user perspective it allows the system to scale to large
geographic areas.


Another new feature of SAFE-T is digital modulation.  Some SAFE-T
talkgroups are digital and others are analog.  Generally, only the
police departments are digital.


How to monitor the system:
The analog talkgroups can be monitored with your typical Uniden and
Radio Shack trunktracker scanners.  The digital talkgroups work the same
as the analog except you need an APCO-25 compatible digital
demodulator/decoder.  One such APCO-25 compatible trunktracker would be
a Uniden BC250D with the optional APCO-25 card.  Theoretically, this
could also be an add-on box or maybe even a computer program.

Current digital scanners are nowhere near as good at demodulating the
digital signals as the Motorola 2-way radios.  Basically, you need a
very strong signal to decode APCO-25 modulation with a Uniden BC250D. 
The Radio Shack PRO-96 promises to be a much nicer radio and hopefully
will provide better digital audio.


Some background on various Motorola Systems:
  http://www.trunkedradio.net/modules.php?name=Content&pa=showpage&pid=1

SAFE-T is a Motorola ASTRO-25 system:
  http://www.trunkedradio.net/modules.php?name=Content&pa=showpage&pid=3


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