Control Channel Only P25 Scanning Question

[KevinC]

That looks like a regular P25 system that uses bandplans.

Don't know what to tell you, it uses explicit entries for the VHF sites.

 

[JoeBearcat]

I wish I could direct you to the system type I'm talking about, but the one I knew of seems to have been updated to a Harris system.

The P25 frequencies had those little black numbers next to them like an LTR system so you knew which slot to program the frequency in.
Do you recall any of those?

I don't think I can search other systems, but other ones (if they still exist) are likely to be in the UHF Fedband.

 

[KevinC]

I wish I could direct you to the system type I'm talking about, but the one I knew of seems to have been updated to a Harris system.

The P25 frequencies had those little black numbers next to them like an LTR system so you knew which slot to program the frequency in.
Do you recall any of those?

I don't think I can search other systems, but other ones (if they still exist) are likely to be in the UHF Fedband.

I'm guessing if the system didn't support multi-block messages you could do it that way. Maybe it was some smaller manufacturer that didn't know how to implement multi-block and just did it the way you saw.

 

[JoeBearcat]

I found another reference to these system types. After the post, GTR again said both explicit and implicit transmit bandplans (contradicting what the poster said).

So what is the P25 system type called that DOES NOT transmit a bandplan? I've always known it as implicit. If it is not that, what are those called?

understanding p25 trunk system information in database

Hi, Totally new to programming radios. Someone gave me a BCD996P2. I'm in the Indianapolis, IN area. I've read through various references and forum questions on this website, and have managed to install FreeScan and program some easy AM channels (e.g. Indy Airport communications, and CB...

forums.radioreference.com

 

[JoeBearcat]

I'm guessing if the system didn't support multi-block messages you could do it that way. Maybe it was some smaller manufacturer that didn't know how to implement multi-block and just did it the way you saw.

This was EF Johnson, and it's not surprising they tried to make the system like LTR where the radio is programmed with the bandplan and the system only sent the table number for the channel assignment data.

But, if neither explicit or implicit applies to those systems, what are they called?
I'm pretty sure the sysop called them implicit.

Do you have access to legacy data from trunked systems that have been updated in the database?
The system I was familiar with is now a Harris system per a RR update a few months ago.

It's entirely possible all these systems have been updated by now, and the terms implicit/explicit have since changed to mean other things.

The Uniden implementation of this is to program the table with the system frequencies (in the correct slot/order) and set the step to any value since it was not used.

I found this excerpt from the BCD996T manual:
" The BCD996T includes two operation modes for P25 systems: explicit mode and implicit mode channel assignment. Explicit mode systems include all information needed to determine voice frequencies on the control channel. You must supply the system’s band plan for implicit systems for the scanner to correctly determine voice frequencies."

That falls in line with my understanding as well - that implicit USED to mean no bandplan was sent on the control channel.

 

[garys]

I've listened to this system a number of times on x36HP scanners. It's Control Channel only, if that helps clear up the confusion. Which I think makes it an implicit system. At least for the 700/800 parts. I've never listened to the VHF section so can't comment.

Is it possible to use different modes for different sites? That system covers a large geographic region, so a mix of implicit and explicit sites may be the only way to get it running.

Greater Austin/Travis Regional Radio System (GATRRS) Trunking System, Austin, Texas

Greater Austin/Travis Regional Radio System (GATRRS) Trunking System Profile

www.radioreference.com

 

[KevinC]

I've listened to this system a number of times on x36HP scanners. It's Control Channel only, if that helps clear up the confusion. Which I think makes it an implicit system. At least for the 700/800 parts. I've never listened to the VHF section so can't comment.

Is it possible to use different modes for different sites? That system covers a large geographic region, so a mix of implicit and explicit sites may be the only way to get it running.

As I posted the VHF sites are explicit.

 

[garys]

The thread posts seem to indicate that it's one or the other as far as how systems work. Which doesn't seem to be the case here. The VHF counties are far from the Travis County area, in some cases I'd estimate a couple of hundred miles away. As such, I'd have to figure that they are using the controller core, but are otherwise independently operated.

The obvious answer is that a mixture of implicit and explicit sites are in operation. I'd guess that systems like this are fairly rare, so maybe it's not a good example to use to explain implicit versus explicit.

As I posted the VHF sites are explicit.

 

[GTR8000]

I've listened to this system a number of times on x36HP scanners. It's Control Channel only, if that helps clear up the confusion. Which I think makes it an implicit system. At least for the 700/800 parts. I've never listened to the VHF section so can't comment.

Is it possible to use different modes for different sites? That system covers a large geographic region, so a mix of implicit and explicit sites may be the only way to get it running.

The thread posts seem to indicate that it's one or the other as far as how systems work. Which doesn't seem to be the case here. The VHF counties are far from the Travis County area, in some cases I'd estimate a couple of hundred miles away. As such, I'd have to figure that they are using the controller core, but are otherwise independently operated.

The obvious answer is that a mixture of implicit and explicit sites are in operation. I'd guess that systems like this are fairly rare, so maybe it's not a good example to use to explain implicit versus explicit.

I thought we covered this already in my earlier post?

Note that a system can use a combination of implicit and explicit signaling. The PA-STARNet system, for example, uses implicit signaling for the UHF, 700, and 800 MHz sites within the system, whereas the majority of VHF sites are using explicit signaling. There are some VHF entries in the band plan, however that does not cover all of the possible channels used on the system, and thus explicit signaling must also be used.

The entire system shares a single band plan, which can contain up to 16 entries. If certain frequencies at certain sites aren't covered by that band plan, they can use explicit mode signaling to provide the subscribers with the RX/TX of the traffic channels.

So whether or not the entire system is implicit or explicit depends on what bands it operates in, and what considerations need to be taken for the frequencies in use. You are most likely to see explicit signaling in use on a system that uses VHF frequencies, either exclusively or mixed with other bands (as in the example of the PA-STARNet P25 system I gave earlier). Most systems that are exclusively implicit are those in the UHF, 700, 800, 900 bands where the repeater offsets are normally fixed.

 

[garys]

So the question is why are you and others beating this to death? It seems to be pretty straightforward.

Note that a system can use a combination of implicit and explicit signaling. The PA-STARNet system, for example, uses implicit signaling for the UHF, 700, and 800 MHz sites within the system, whereas the majority of VHF sites are using explicit signaling. There are some VHF entries in the band plan, however that does not cover all of the possible channels used on the system, and thus explicit signaling must also be used.

 

[GTR8000]

So the question is why are you and others beating this to death? It seems to be pretty straightforward.

I'm sorry, is our discussion bothering you? No one forced you to participate in this thread, last I checked.

I'm not beating anything to death, I'm simply pointing out that Uniden America's new Product Manager has at least twice posted something inaccurate when it comes to implicit/explicit P25 signaling. Sorry, but someone in that position should probably get a handle on the concept before making inaccurate posts.

I tried to explain this to him a month ago in this thread: SDS200 Squelch. 1= Static , 2= Not sensitive enough

 

[MStep]

So the question is why are you and others beating this to death? It seems to be pretty straightforward.

Let them keep beating it to death----- I'm learning a lot about "Control Channel Only" operations, and sometimes it's gotta be explained 20 different ways before I start to get the gist.

Keep it going guys.

 

[GTR8000]

It is worth pointing out that "Control Channel Only" is not necessarily exactly the same concept as P25 implicit/explicit signaling.

What I mean by that is, P25 is inherently a "control channel only" type of trunking, whereby the actual subscriber radios process the information being broadcast over the site's control channel, and act on those messages. The majority of systems use implicit signaling to direct the radio to the proper traffic channel (voice or data frequency) based on the predefined band plan that is both in the radio's codeplug as well as broadcast over the control channels (the IDEN_UP messages), while other systems use explicit signaling to direct the radio to the proper traffic channel not based on the predefined band plan, but instead by providing explicit instructions on which frequencies to use for both RX and TX.

"Control Channel Only" has a specific meaning as pertains to Uniden scanners trunk tracking P25 systems, in particular some of the older models, as all of the newer models are inherently "CC Only" from at least the XT series forward. In a nutshell, some of the older models required a band plan to be manually entered, along with all system frequencies (control and traffic) in order for the scanner to properly track the conversations. Those models were apparently unable to decode the over-the-air band plan for implicit systems or the multi-block messaging for explicit systems.

That is all a thing of the past, as all modern Uniden scanners are able to tune to the correct traffic frequencies even when only the active control channel's frequency has been programmed. None of the traffic frequencies need to be programmed, nor does a band plan need to be manually programmed. It's all figured out via the control channel messaging, same way a real subscriber radio would do so.

I'm not really sure where the disconnect is between these fairly simple concepts and the misunderstanding or conflating with other system types. At this point I'm not sure there is anything else I could possibly add to provide more clarity. I suppose from that standpoint, maybe I do agree with @garys that we're beating a dead horse. Either you understand implicit/explicit and how it does or doesn't relate to Uniden's "Control Channel Only" mode, or you don't. I just don't appreciate being told that I'm beating it to death, when all I'm trying to do is clarify and educate, in order to actually prevent further confusion. When the Uniden Product Manager posts, people are naturally going to take some of that as gospel, and so errors in those posts (especially when they have been repeated multiple times) should be addressed.

 

[JoeBearcat]

I thought we covered this already in my earlier post?

You described two systems for implicit and explicit - neither of which are the system type I'm talking about that was said to be implicit by the system manager because it did not transmit bandplans, but only table assignments.

Note that a system can use a combination of implicit and explicit signaling. The PA-STARNet system, for example, uses implicit signaling for the UHF, 700, and 800 MHz sites within the system, whereas the majority of VHF sites are using explicit signaling. There are some VHF entries in the band plan, however that does not cover all of the possible channels used on the system, and thus explicit signaling must also be used.

I happen to be familiar with this system, and I have never seen any frequency assignment that is not using a bandplan assignment. Virtually every frequency is covered. The first four entries are always 800/700 MHz. The remainder are for the band used by the site.

In fact, let's review it: (if this will post correctly)



As you can see, the bandplan covers every 800, 700, and VHF frequency in Phase I or Phase II in 2.5 kHz steps. UHF excludes some of the T-band but covers every frequency 450-481(and change)MHz at 6.25 kHz steps. So every frequency used is in the table allocation. BTW, CH# = max except for one entry I forgot to max out. So freq calc is the max frequency for that entry except for table 4 (which covers to 174.9975 MHz). VHF would use tables 8 and 11 for the most part to cover 150-174 MHz. Checking a few sites, they are using 8, 10, and 11 on VHF.

So Starnet seems to be a regular P25 system just like nearly any other Motorola Phase II system. It definitely uses tables for the assignments.

 

[JoeBearcat]

I'm not beating anything to death, I'm simply pointing out that Uniden America's new Product Manager has at least twice posted something inaccurate when it comes to implicit/explicit P25 signaling. Sorry, but someone in that position should probably get a handle on the concept before making inaccurate posts.

I tried to explain this to him a month ago in this thread: SDS200 Squelch. 1= Static , 2= Not sensitive enough

That's funny after I said very early on that I might be wrong, but there has yet to be an answer given on the type of system I have always known as implicit that uses no bandplans and assigns voice channels based on one of the 16 table entries. Everyone seems to say that is not implicit, but defines implicit and explicit as bandplan-based.

If I'm wrong, what type system have I been describing? What is the new name for that system type? Nobody can seem to answer that.

My terms USED to be accurate based on the industry. It seems some definitions changed, and I am the person who asked for clarification which I have yet to receive.

The longer this thread continues, the more it seems to prove there is no standard and no answer. You keep describing systems that do not match what used to be called an implicit system. I'm fine with admitting this is yet another area where terms are mutable, but if there is an answer I would like to know it. So far, there seems to be none aside from the statement that implicit means something different now, and there is no terms for the old implicit system type that uses no bandplan (or more specifically one frequency per bandplan table).

 

[JoeBearcat]

Those models were apparently unable to decode the over-the-air band plan for implicit systems or the multi-block messaging for explicit systems.

This is rather difficult to do when no bandplan is transmitted as is the case in the system I have been trying to get the accurate term for.

 

[GTR8000]

You described two systems for implicit and explicit - neither of which are the system type I'm talking about that was said to be implicit by the system manager because it did not transmit bandplans, but only table assignments.

I very much doubt it was a P25 system if it didn't transmit IDEN_UP messages, aka a Channel ID plan, aka a Band Plan, aka the 16 channel table.

I happen to be familiar with this system, and I have never seen any frequency assignment that is not using a bandplan assignment. Virtually every frequency is covered. The first four entries are always 800/700 MHz. The remainder are for the band used by the site.

As you can see, the bandplan covers every 800, 700, and VHF frequency in Phase I or Phase II in 2.5 kHz steps. UHF excludes some of the T-band but covers every frequency 450-481(and change)MHz at 6.25 kHz steps. So every frequency used is in the table allocation. BTW, CH# = max except for one entry I forgot to max out. So freq calc is the max frequency for that entry except for table 4 (which covers to 174.9975 MHz). VHF would use tables 8 and 11 for the most part to cover 150-174 MHz. Checking a few sites, they are using 8, 10, and 11 on VHF.

So Starnet seems to be a regular P25 system just like nearly any other Motorola Phase II system. It definitely uses tables for the assignments.

I know you're familiar with that system, which is why I used it as an example. You are being fooled into believing that this 16 channel band plan covers every VHF possibility, which it most certain does not.

You are forgetting about one key fact, which is that VHF does not use standard offsets (inputs), and in many cases sites are using a variety of inputs that don't necessarily jive up with that broadcast band plan. You may have a repeater output of 155.670 in the western part of the state using 159.08 as the input, whereas a repeater output of 155.670 in the eastern part of the state uses 151.8175 as the input. Now, do you see the problem with that 16 channel band plan, and how it could not possibly cover every permutation of output/input for VHF? The other bands aren't an issue...+5 on UHF, +30 on 700, -45 on 800...done.

Run Unitrunker or your favorite P25 decoding software on your local STARNet VHF site(s), and enable control channel logging. Look at the raw log whenever there is a TDMA transmission on VHF, and look for the multi-block signaling. That is explicit mode, using two TSBK's to provide both the RX and TX frequencies for the channel.

If you're lucky enough to be within range of an 800 site, which I believe that you are, do the same and watch how all of the channel grants are single-block signaling referencing the Ch ID from the band plan. That is implicit mode, using one TSBK to direct the radio to reference the channel plan/band plan/16 channel table.

That's funny after I said very early on that I might be wrong, but there has yet to be an answer given on the type of system I have always known as implicit that uses no bandplans and assigns voice channels based on one of the 16 table entries.

Band plan = "16 table entry". You are literally describing the same thing using different terms. Any site in a system that relies solely on the band plan/16 table entry/Channel ID plan/etc. is using implicit signaling, period. If the channel assignments are not able to be covered by the 16 entries in the table/band plan, then the system must use explicit signaling to some degree.

If you want to take this discussion off the forum so we can go into more detail, feel free to PM me and we'll either chat there or via email. This is probably getting a bit tedious for most users on the forum.

 

[MStep]

If you want to take this discussion off the forum so we can go into more detail, feel free to PM me and we'll either chat there or via email. This is probably getting a bit tedious for most users on the forum.

Hi GTR and Joe,

I think a lot of folks (like myself) are getting quite an education about the many intricacies of "Control Channel Only"--- I for one did not realize the complexity of systems and/or how the SDS series handles these complexities.

It may be "repetitive" to some, but I find your knowledge about this stuff fascinating, both of you guys. I wish you would just keep it public so that anyone and everyone who wants to learn can pick up as much knowledge as possible can do so.. GTR, you're practically writing a manual right here on Radio Reference about stuff that I imagine many of us have only scratched the surface of. So unless there is some Uniden propriety information and/or military secrets involved, I would love to keep reading about this stuff. There have to be at least a few others trying to follow along and gain knowledge.

That's all I can possibly contribute to this conversation. But this is the kind of real "meat & potatoes" that keep many of us so fascinated about different communications systems.

Those who find this boring or repetitive can simply ignore the thread. Of course, it's up to you guys, but that's my 2 cents.

 

[GTR8000]

@JoeBearcat If I'm coming across as impatient or salty, I apologize. I'll take a few deep breaths and check back tomorrow to see if I've clarified anything or if we need to go through some more examples, or a deep dive to try to find out what system you might be thinking about from yesteryear.

 

[KevinC]

You described two systems for implicit and explicit - neither of which are the system type I'm talking about that was said to be implicit by the system manager because it did not transmit bandplans, but only table assignments.



I happen to be familiar with this system, and I have never seen any frequency assignment that is not using a bandplan assignment. Virtually every frequency is covered. The first four entries are always 800/700 MHz. The remainder are for the band used by the site.

In fact, let's review it: (if this will post correctly)

View attachment 101483

As you can see, the bandplan covers every 800, 700, and VHF frequency in Phase I or Phase II in 2.5 kHz steps. UHF excludes some of the T-band but covers every frequency 450-481(and change)MHz at 6.25 kHz steps. So every frequency used is in the table allocation. BTW, CH# = max except for one entry I forgot to max out. So freq calc is the max frequency for that entry except for table 4 (which covers to 174.9975 MHz). VHF would use tables 8 and 11 for the most part to cover 150-174 MHz. Checking a few sites, they are using 8, 10, and 11 on VHF.

So Starnet seems to be a regular P25 system just like nearly any other Motorola Phase II system. It definitely uses tables for the assignments.

In your example how does the system calculate what TX frequency the subscriber should use for VHF? It can't as VHF doesn't have a standard TX/RX split, whereas 7/800 and UHF do. So the TX OTA assignment must be coming form somewhere else and that somewhere else is the multi-block messages (which have both the TX and RX frequencies the subscriber is to use for that channel assignment in them, hence explicit).