800MHz Trunked Radio - How does it work

wtnfs · Mar 6, 2015

I am trying to better understand how all these 800MHz trunked systems work. I am not completely stupid with it, but some of it just makes very little sense to me. When I try to have it explained by some, I get lost in translation.

What are the different systems in Colorado? - DTRS, West Metro/Lakewood, Denver (MetroNet?), Westy (?), FRCC

Are these different systems using different 800MHz frequencies?

How do the MAC and Network First talkgroups tie into each of these systems? (I think the NF are IP connected but not sure on the MAC's).

Can a talkgroup on DTRS work on FRCC or other system if given the info? (System Keys, NAC's, etc.)

When someone says "channel" in reference to a repeater, I am sure they are not talking about a talkgroup so what is a channel? Is this a trunked channel?

What are some causes that would have a handheld XTS2500 hit a repeater (gets the chirp with pressing the PTT) but no voice being transmitted?

Thanks for any insight.

fireemt55 · Mar 6, 2015

Use the Wiki

Agreed it can be confusing at times. Click the Wiki Button at the top of the page and read the excellent information contained within, especially Trunking Basics - The RadioReference Wiki. This will likely answer a majority of your questions.

LMR_Dude · Mar 6, 2015

Ill take a stab at some of your questions.

wtnfs said:
I am trying to better understand how all these 800MHz trunked systems work. I am not completely stupid with it, but some of it just makes very little sense to me. When I try to have it explained by some, I get lost in translation.

What are the different systems in Colorado? - DTRS, West Metro/Lakewood, Denver (MetroNet?), Westy (?), FRCC.

- DTRS is the statewide Motorola radio system used by CSP and some counties and cities. West Metro/Lakewood/Denver/Arvada use the MARC (Metro Area Radio Consortium) which is a Harris radio system. Westy uses Cassidian radio system (I'm hazy on the details). FRCC is a Motorola system up north, I don't know its boundaries.

Are these different systems using different 800MHz frequencies?
- Yes, however its possible the same frequency could be used IF interference concerns are mitigated.

How do the MAC and Network First talkgroups tie into each of these systems? (I think the NF are IP connected but not sure on the MAC's).
- MAC (Mutual Aid Channels) are DTRS talkgroups (TGs), they can be programmed into radios if there are agreements between CNCC, the folks who manage the DTRS, and the requesting agency. Network First TGs exist in all systems that want them (MARC, Denver EDACS, DTRS etc.) communications on ANY of the NF TGs will appear in the others systems as that same NF TG name. So if you transmit on Blue SE while logged into MARC your voice would also come over the DTRS system on Blue SE. Totally different radio systems, frequencies and models of radio but complete interoperability.

Can a talkgroup on DTRS work on FRCC or other system if given the info? (System Keys, NAC's, etc.)
- IF, and I capitalized it intentionally, there is the will to have TGs appear on other systems it can be made to happen. Since the adoption on P25, different vendors radio can be used on another vendors systems.

When someone says "channel" in reference to a repeater, I am sure they are not talking about a talkgroup so what is a channel? Is this a trunked channel?
-Channel, in the technical sense, does refer to a repeater or frequency. However, the terms channel, frequency and TG sometimes get used interchangeably (which sometimes results in confusion).

What are some causes that would have a handheld XTS2500 hit a repeater (gets the chirp with pressing the PTT) but no voice being transmitted?
-Sorry, there are to many variables for me to answer this question.

Thanks for any insight.

Spitfire8520 · Mar 6, 2015

LMR Dude has a fairly comprehensive answer, so I'll see if I can improve on some of them.

wtnfs said:
What are the different systems in Colorado? - DTRS, West Metro/Lakewood, Denver (MetroNet?), Westy (?), FRCC

Most of this has been answered, but FRCC is a Motorola system that primarily services agencies within Adams and Weld County only. MetroNet is not a system, but a talkgroup that is shared between the systems that is used for dispatcher to dispatcher communications, very similar to a Network First talkgroup.

wtnfs said:
How do the MAC and Network First talkgroups tie into each of these systems? (I think the NF are IP connected but not sure on the MAC's).

MAC only applied to DTRS users (at this time). FRCC may see MACs in the future (see the next question). I'm under the impression that anyone who is a DTRS user will have the MAC talkgroups programmed into their radios for interoperability.

Network First only applies in the the Denver Metro area as this time. Network First is (I believe) a Harris solution that was deployed by Denver for Denver Metro area interoperability to patch dissimilar radio systems into each other. It currently patches DTRS, Denver EDACS, MARC, Aurora EDACS, Boulder VHF. It formerly included Arvada/Westminster EDACS before both cities moved system. I believe Westminster no longer has a NWF patch and is using DTRS for NWF. NWF is not currently connected via IP, but it is currently being moved to IP via P25 ISSI.

wtnfs said:
Can a talkgroup on DTRS work on FRCC or other system if given the info? (System Keys, NAC's, etc.)

I believe it may be possible via P25 ISSI once it is deployed, but it depends on the politics of how the different radio admins want to do this. Currently, there is no agency has talkgroup roaming between systems (NWF would likely be the first to do so), however you can have talkgroups on a different system programmed into your radio if you have the proper keys.

poltergeisty · Mar 10, 2015

Here's my simple explanation. :lol:

You have a control channel (frequency) that for lack of a better word issues system frequencies to users. There may be a total of ten frequencies for the tower with a control channel. At any one time PD and fire can use the same frequency depending on who is currently using it. It's like standing in line at a self check out in a store and waiting for the next available POS (Point Of Sale) to become available. Each POS is the system frequency.

Another way of looking at it is by a traffic cop directing traffic. The traffic cop is the control channel and he is directing which car to go left or right which would be like a system channel. Basically the control channel dictates what system channel you will use.

Cell phones work in the same way. And did you know text messages ride on the control channel? Yet they nickel and dime you for it. :lol:

Channel is another name for frequency. Talkgroups are just voice paths (for lack of a better word) that share the set amount of system frequencies (channels) on a tower. So I guess if a tower had 10 system channels then ten talkgroups could all talk at the same time. But that never happens most of the time. With a trunked system you may have a talkgrop ID of 3000 and when you key up on the radio you may be transmitting on 867.700. Then when you key up again you may be transmitting on 867.600. It all depends who is is using what system channel dictated by how the control channel assigns you that system frequency, (channel). At the same time talkgroup 3000 is transmitting on one system frequency talkgroup 4000 can be on another system frequency. All the system frequencies get reused. At one moment you could be on system frequency 867.600 and at another moment you could be on system frequency 867.700.

Do you know how sub codes work in analog radio? It's kinda like that where a sub code could be analogous to a talkgroup. You can have multiple users per frequency.

The nature of digital is a headache. But if you think of it logically it makes sense. Each user = A talkgroup. Each talkgroup can talk on any one given system frequency dictated by the control channel.(frequency). The control channel ( frequency) dishes out what system frequency you (the talkgroup) will use from one transmission to the next.

800MHz Trunked Radio - How does it work

wtnfs

Member

fireemt55

Member

LMR_Dude

Member

Spitfire8520

I might be completely clueless! =)

poltergeisty

Truth is a force of nature

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