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Old 04-30-2017, 10:36 PM
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Default P25 Phase I question

Hello,
This may be a rather stupid question, but I have recently purchased a TRX-2 and am monitoring my first P25 system. Being used to listening to EDACS with one site, I have a rather simple question about P25. Are all talkgroups of the system available at all sites of a system? Specifically on a state-wide system like Colorado's DTRS? For example, if I am receiving a site across the state from a particular talkgroup, will the site still transmit it regardless of distance?
Thanks,
Mike
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Old 05-01-2017, 8:48 AM
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It all depends on how the system is geographically and how its set-up.
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Old 05-01-2017, 8:57 AM
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In Illinois on Starcom21 (P25), the towers only transmit a talk group if a client radio in range. So say if a Belvidere unit goes to Springfield, they could talk to the local dispatch like they're in the county. But I could not be in Springfield and listen to Belvidere on a scanner. Around here, you might get 1 or 2 counties away and not be able to listen to the county you want.
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Old 05-01-2017, 9:07 AM
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AstroTrunking in multi-zone applications functions essentially the same as SmartZone trunking.

As a general proposition, a talkgroup can be programmed to be handled one of three ways:

1) System-Wide: A group call channel grant in any zone will cause the assignment of a voice channel on all zones (or selected zones) and audio will be passed regardless of non-initiator affiliation. This should be used sparingly, as it is very intensive of resources; in general, it is intended for applications where field personnel are distributed throughout the system area but all dispatch is handled at one location.

2) Local Only: This talk group is limited to use in only a single zone. A user selected on this talkgroup will not affiliate in any other zone. This option is intended for applications where a talkgroup use is limited to an institution whose users are confined to a single geographic area.

3) Typical SmartZone: A group call channel grant in any zone will cause a voice channel also to be allocated in any other zone in which a user selected on the talkgroup has previously affiliated. This is intended to address two situations: where users have system wide duties that may result in their roaming anywhere in the system coverage area, and users whose duties tend to draw them proximate to nominal zone geographic "boundaries."

Caution: the foregoing is simplified. There are umpteen different ways to configure a system to meet different needs while minimizing the load on system resources.
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Old 05-01-2017, 6:17 PM
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Quote:
Originally Posted by MCD95 View Post
Hello,
This may be a rather stupid question, but I have recently purchased a TRX-2 and am monitoring my first P25 system. Being used to listening to EDACS with one site, I have a rather simple question about P25. Are all talkgroups of the system available at all sites of a system? Specifically on a state-wide system like Colorado's DTRS? For example, if I am receiving a site across the state from a particular talkgroup, will the site still transmit it regardless of distance?
Thanks,
Mike
Hi!

Pretty much all of the multi-site networked systems in Colorado operate on the concept of affiliation. In order for a site to carry a particular talkgroup's traffic, a user radio would need to affiliate (or "check in) to that site with that particular talkgroup.

It is due to the limitation that each site has a limited number of frequencies it can use at once. This can be seen in the database for each individual site. If all the sites carried all the talkgroups for the system, they would likely need hundreds of frequencies per site.

An actual system radio is pretty much be able to use any talkgroup from anywhere in the state. A scanner needs to find a site that has a system radio affiliated to that talkgroup. It is unlikely for a scanner to hear talkgroups used outside of the site's coverage area. The exception is if radio roams into the area while actively using that talkgroup. This happens occasionally with things like jail and ambulance transports from across the state, but it is not a reliably way of listening to traffic from across the state.

There are a few special cases for Colorado DTRS that I won't get into unless you are interested. If you have Colorado specific questions in the future, fell free to ask them in Colorado Radio Discussion Forum. We have a good group of very knowledgeable users over there.
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Old 05-01-2017, 6:27 PM
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Quote:
Originally Posted by Spitfire8520 View Post
Hi!

Pretty much all of the multi-site networked systems in Colorado operate on the concept of affiliation. In order for a site to carry a particular talkgroup's traffic, a user radio would need to affiliate (or "check in) to that site with that particular talkgroup.

It is due to the limitation that each site has a limited number of frequencies it can use at once. This can be seen in the database for each individual site. If all the sites carried all the talkgroups for the system, they would likely need hundreds of frequencies per site.

An actual system radio is pretty much be able to use any talkgroup from anywhere in the state. A scanner needs to find a site that has a system radio affiliated to that talkgroup. It is unlikely for a scanner to hear talkgroups used outside of the site's coverage area. The exception is if radio roams into the area while actively using that talkgroup. This happens occasionally with things like jail and ambulance transports from across the state, but it is not a reliably way of listening to traffic from across the state.

There are a few special cases for Colorado DTRS that I won't get into unless you are interested. If you have Colorado specific questions in the future, fell free to ask them in Colorado Radio Discussion Forum. We have a good group of very knowledgeable users over there.
So if I live in county 1 and want to receive the neighboring County 2's comms, should I just add the nearest County 2 site into the system? I'm barley outside of the range circle according to RR database, would I be able to receive the neighboring counties comms on my town site, or just program both and see how good the signal is?
Thank all of you,
Mike
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Old 05-01-2017, 8:19 PM
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Listening to a statewide system has two major components. One is the sites and the other is the talkgroups.

In the beginning, its better to cast a wide net and program any sites you think you might hear. So yes, programming adjacent county sites is worth trying. At some later time you can revise your programming to lockout sites too far away to receive.

Also, you'll want to program the talkgroups for adjacent counties.

Lastly, don't forget about including any statewide mutual aid channels. They could show up on any given site.
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Old 05-01-2017, 8:54 PM
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Quote:
Originally Posted by MCD95 View Post
Are all talkgroups of the system available at all sites of a system? Specifically on a state-wide system like Colorado's DTRS? For example, if I am receiving a site across the state from a particular talkgroup, will the site still transmit it regardless of distance?
No. It would be impossible for a large system to carry every call on every site. How would a ten channel site carry fifty simultaneous calls?


Quote:
Originally Posted by MCD95 View Post
So if I live in county 1 and want to receive the neighboring County 2's comms, should I just add the nearest County 2 site into the system? I'm barley outside of the range circle according to RR database, would I be able to receive the neighboring counties comms on my town site, or just program both and see how good the signal is?
Range circles don't account for terrain. Manually tune to the County 2 site's control channel and see if your scanner can receive it. That should dictate your actions.
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Old 05-02-2017, 2:24 AM
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Quote:
Originally Posted by MCD95 View Post
So if I live in county 1 and want to receive the neighboring County 2's comms, should I just add the nearest County 2 site into the system? I'm barley outside of the range circle according to RR database, would I be able to receive the neighboring counties comms on my town site, or just program both and see how good the signal is?
Thank all of you,
Mike
There are a lot a variables that go into monitoring, so it is hard to say without more specifics. The site in County 1 might have very good coverage over County 2, so it is possible that County 2's traffic will be on your local site all day long. There is also a special case where the site near you might be configured to reject radios from County 2. Experimenting would probably be the best way of figuring out what works out in your area.

If you want to be certain about receiving County 2, it would probably be a good idea to program a site located within County 2. Those that are really picky about which site they are scanning will duplicate the system multiple times and only program a single site for each duplicated system. I have a system where I have a bunch of sites for general scanning, and I have several sites programmed as their own system with a few talkgroups that I know can be heard for listening to specific traffic.

Specific examples are sites like Riley (1-002), Thorodin (1-005), Squaw (1-006), Smoky Hill (1-007), and Lookout (1-008) which cover large areas and can have a lot of varied traffic. This is why you tend to see a lot of frequencies associated to those sites as they can be busy during the day. At night, when there are a lot less radios, they may become less reliable since there is a reduced chance that there is a radio actively using that site.

Some of the sites are configured to only let very specific talkgroups through. DIA (1-068) and Birch (1-069) is an example of RTD owned DTRS sites which basically only ever carry RTD traffic. Those sites are pretty much useless to program unless you want to monitor RTD.

The range circles in the database is fairly inaccurate (and it is a pain to try to correct them). I would not trust them over your personal experience. Terrain is a very big factor for this. You will likely find that you can't receive sites that the database says you can and get sites clearly that the database said you can't.
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