[ETS/PARC List] P25 Trunking Followup Notes

[Len Griffin]

Hope everyone enjoyed the presentation as I enjoyed researching it.

 

Here are some points I may have forgotten:

 

1] The scanner will be listening to ' SYSTEMS ' that have MANY subscribers.
If you allow it to SCAN all the systems you have programmed, it will take a
LONG time to return to the current conversation. It is best to stay on ONE
system and let it scan the talkgroups on a single system. Remember, it takes
time to find and lock onto the control channel, so if you are scanning
SYSTEMS, transmissions may not be complete.

 

2] The Trunked SYSTEMS use mainly directional antennas. You have to be in
the antennas pattern to hear them. Most have multiple sites, so it is
usually not a problem. Lots of the die hard scanner people have put up
multiple directional antennas, and use combiners fed by hardline to feed
their scanner. Too much for me!

 

3] At RadioReference, there is a terrific discussion at the top of the '
FORUMS ' page about the NJICS system, started in July 2017. It has new info
added every day. This system is still evolving, with new users joining the
system. Note that many counties have their own trunked system, as well as
access to NJICS.

forums.radioreference.com

 

4] The NJICS has 538 talkgroups, as you saw. Not ALL of them will be on a
given tower at the same time. I was reading a radio reference NJICS
discussion this morning, and came across this great explanation:

 

The most important variable is that the NJICS system is comprised of many
individual standalone sites, along with a few simulcast cells. ASTRO 25
(Motorola P25) systems are by nature designed to default towards conserving
channel resources. If a standalone site only has a limited pool of 3-4
channels (one of which is a full-time control channel), then you want to
make sure you're not wasting channels by having talkgroups broadcasting at
that site that aren't required by the users in the area. In that respect,
the system is designed to only carry talkgroup traffic when a radio
registered at the site is affiliated with said talkgroup(s).

Of course there are always exceptions to the basic rules, and in this case,
the exception is that the system administrators can "force" any talkgroup
they want to be carried at any site(s) they want, regardless of whether any
radios are affiliated with those talkgroups at said sites. There are some
examples of those talkgroups on the NJICS which seem to be carried at every
site 24/7 no matter what, DEP Park Police Dispatch seemingly being one of
them.

As far as the SmartX converters are concerned, they simply allow for the
matching talkgroups to be linked together on both systems. The link is
bidirectional, so that no matter which system a radio is operating on, the
audio will be heard on the same talkgroup on the other system. The caveat is
as noted above, that at least one radio must be affiliated with that
talkgroup at one or more sites on the other system, or the talkgroups must
be forced by the system admins to be carried regardless of affiliation
status. If neither of those criteria are met, then the talkgroup will remain
active on only one system. The default setting is "on-demand", so to speak.

That's why often the NJSP talkgroups come and go across various sites on the
NJICS system. If a 700 MHz radio happens to affiliate with 2-COMM in
northwest Sussex County, it will cause the 2-COMM talkgroup to be carried on
High Point. If that radio roams south, it will eventually find a stronger
signal from the Walpack site, at which point two things will happen: #1 the
radio will deregister from High Point, causing the 2-COMM talkgroup to stop
being carried at that site (assuming no other radios are affiliated with
that talkgroup at that site), and #2 the radio will register on Walpack and
will cause the 2-COMM talkgroup to follow it to that site.

The same holds true for talkgroups that are primarily on the NJICS system
now. Even if there is a matching counterpart on the 800 system (DRJTBC
talkgroups, for example), they will only be heard if #1 a radio is
affiliated with one of the 800 MHz simulcast cells, or #2 they are being
forced to be carried on the 800 MHz even in the absence of any radios
actually registered on 800 MHz and affiliated with one of those talkgroups.

Oh and finally, talkgroups can actually be restricted by site. Newark Fire
talkgroups, for example, are only permitted on certain sites. A radio that
tries to affiliate with one of those talkgroups on High Point in Sussex
County is going to be denied affiliation. This is also to preserve channel
resources. Other talkgroups are permitted at any site throughout the state.

Basically, there is quite a bit of flexibility in how these systems operate,
and therefore the answer is wholly dependent on how the systems and
individual talkgroups are setup.

 

LEN

WB2HKK