Determining LCN for Connect Plus w/ DSDPlus and one SDR

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Gilligan

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I've been searching out a bunch of systems with DSDPlus and so far I've come across a challenge that I don't understand. At the time, let's say that I'm limited to using a single RTL-SDR unit as opposed to having two. If I had two units, one could watch the control channel and the other could determine the LCN of the voice channels.

With Capacity Plus systems, DSDPlus seems to have no problem determining LCN if there is enough traffic on the system. After monitoring a huge bunch of Connect Plus frequencies, however, it seems unable to be able to determine the LCN of those Con+ voice channels.

Also confusing is that here is the info from the Uniden page for the BCD436HP LCN Finder: For MotoTRBO Connect Plus and DMR Tier III systems, the LCN finder will help to determine the correct LCN assignments for each frequency. Note that this function depends on the system having voice traffic. If this is a slow system, it can take a very long time to determine the correct LCNs.... For a Capacity Plus system to find another LCN, there must be at least two simultaneous comms on the system. On a slow system, it could take many hours to determine all the LCNs. If the control channel signal is lost for more than 10 seconds, the LCN finder will reset.

Honestly I don't know that I've ever had success determining LCN of a Connect Plus system on my BCD436HP. But according to the 'manual', it's possible. So my question is this: If it is indeed possible to determine the LCN of a Connect Plus system with the BCD436HP, which can only monitor one frequency at a time, is this also possible with DSD+? And if so, is there a trick to getting it to display that as opposed to with Capacity Plus systems? It seems like if the theory is openly known, it would be implemented. Maybe I'm missing something...
 
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DaveNF2G

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Are you sure you don't have CON+ and CAP+ reversed.

Connect Plus has a control channel and will tell you the LCNs.
 

mtindor

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Are you sure you don't have CON+ and CAP+ reversed.

Connect Plus has a control channel and will tell you the LCNs.

Conn+ does not provide LCN information on the voice channel. Sure, the control channel will reveal what LCNs are in use, but of course those aren't mapped to frequencies until you manually or otherwise determine the LCN<-->frequency relationship.

Just monitoring a Conn+ control panel via any method (scanner / SDR) will never reveal actual voice frequencies are associated with particular LCNs, and that is what Gilligan is asking about.

Mike
 

Gilligan

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Conn+ does not provide LCN information on the voice channel. Just monitoring a Conn+ control panel via any method (scanner / SDR) will never reveal actual voice frequencies are associated with particular LCNs, and that is what Gilligan is asking about.

Mike
Exactly... I don't understand how Uniden can advertise this capability and yet it isn't possible in DSDPlus. I'm thinking perhaps it's a mistake in the Uniden write-up, since DSDPlus usually gives way more information about a frequency than the scanner.
 

UPMan

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We use a statistical correlation of channel grants/updates vs active frequencies. It is not a mistake.
 

mtindor

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I've been searching out a bunch of systems with DSDPlus and so far I've come across a challenge that I don't understand. At the time, let's say that I'm limited to using a single RTL-SDR unit as opposed to having two. If I had two units, one could watch the control channel and the other could determine the LCN of the voice channels.

With Capacity Plus systems, DSDPlus seems to have no problem determining LCN if there is enough traffic on the system. After monitoring a huge bunch of Connect Plus frequencies, however, it seems unable to be able to determine the LCN of those Con+ voice channels.

Also confusing is that here is the info from the Uniden page for the BCD436HP LCN Finder: For MotoTRBO Connect Plus and DMR Tier III systems, the LCN finder will help to determine the correct LCN assignments for each frequency. Note that this function depends on the system having voice traffic. If this is a slow system, it can take a very long time to determine the correct LCNs.... For a Capacity Plus system to find another LCN, there must be at least two simultaneous comms on the system. On a slow system, it could take many hours to determine all the LCNs. If the control channel signal is lost for more than 10 seconds, the LCN finder will reset.

Honestly I don't know that I've ever had success determining LCN of a Connect Plus system on my BCD436HP. But according to the 'manual', it's possible. So my question is this: If it is indeed possible to determine the LCN of a Connect Plus system with the BCD436HP, which can only monitor one frequency at a time, is this also possible with DSD+? And if so, is there a trick to getting it to display that as opposed to with Capacity Plus systems? It seems like if the theory is openly known, it would be implemented. Maybe I'm missing something...

The LCN finder does work on Con+. But it requires that you at least know what frequencies could be / are part of the trunked site and program them in.

The reason why the manual states that there needs to be activity is because the LCN info is only obtained from the control channel. When using the LCN finder, it will watch the control channel. When the control states that a particular LCN is in use, the scanner will immediately attempt to scan through all of the frequencies you have programmed in for that site to find a DMR voice signal. [I'm not sure if it requires a valid color code]. The voice channel transmission will indicate that it is part of system ###, Site ###.

So if the control channel says that LCN 3 is active, it then searches the other frequencies programmed in for that site. When it finds a DMR voice signal that is part of that system-site, it'll tag it with the LCN that was obtained from the control channel. I'm sure that it has more logic to deal with the possibility that multiple LCNs are active at the same time. Obviously if two LCNs are active and it goes searching for voice channels, it has no way of knowing which voice frequency is associated with which LCN. The only way it can determine that 100% is for 1 LCN to be active and one voice channel for system-site to be found. And I'm guessing that once a particular LCN<->frequency pairing is discovered, it knows not to bother checking that voice frequency in the future and it probably ignores further activity reported on that particular LCN by the control channel.

If the system is not active with voice, there is absolutely no way for the LCN finder to do it's job. The LCN finder specifically relies upon (a) grabbing the system#-site# info from the control channel, (b) waiting for the control channel to state that an LCN is active, and then (c) searching through the voice frequencies to determine which ones are active and part of system#-site# so that it can attempt to pair them up.

Because of the way LCN finder has to work [and I really don't think there is a better way], the more frequencies you add to the site, the longer it'll take to find the LCNs. And if you add frequencies to the site that aren't actively part of the site, you'll never get a x/y report stating that all channels have been found. the ratio will always be something less than 100% unless you have the active frequencies on the site, and no others, programmed into that site. Of course, none of us ever do that because we are using LCN finder to actually find out whihc ones are active.

I've probably only served to make this very confusing . Sorry for that.

Sans LCN Finder, you can attempt to mimic this behavior manually, to some extent.

1. Run DSDPlus on the control channel
2. Program all frequencies that you think may be part of a site into a scanner

For #2, it makes no difference if you are using a digital scanner or not. You're going to get your mind / ears involved in the process.

Let's assume you have 8 frequencies programmed into a conventional bank on a scanner -- frequencies that you think could be part of a specific site. Well, when you see DSDPlus report an active LCN (talkgroup activity indicated on a particular LCN), the scanner [which by then would be scanning the conventional bank] would stop on a DMR signal and you would hear that DMR signal. You could then determine (not with 100% certainty but likely close enough) that LCN # is associated with whatever frequency the scanner stopped on.

Of course you will want do this more than once for a particular LCN, because there i a chance that more than one of the programmed frequencies in the conventional bank could have DMR on them simultaneously (but not both be part of the same system#-site#).

If it were me, I'd watch DSDPlus and wait for it to report an LCN in use with voice comms. I'd then make note of what DMR signal the scanner stopped on. While the LCN was still reported as active with a voice conversation, I'd hurry up and force the scanner to continue scanning again to see if it stops on the same frequency/DMR signal. I'd do that as fast as possible a couple of times to be sure [in my mind] that that particular frequency with DMR audio (or raw DMR) is actually associated with the LCN being reported on DSDPLus.

The LCN Finder has a benefit of (a) being able to detect a DMR signal, (b) likely being able to read the system#-site# ID broadcast by the voice channel to provide additional confidence in the finding -- that extra bit of confidence is what you dont' have when you are doing it "by ear".

But doing it by ear is extremely effective and is how I've discovered many LCN<->frequency relationships for Con+ systems.

Mike

PS: As a disclaimer, I have no idea what logic is included in the LCN Finder. I just know it works, and I've guesstimated as to how it might be functioning. Paul obviously knows the nitty gritty about it.
 

mtindor

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Exactly... I don't understand how Uniden can advertise this capability and yet it isn't possible in DSDPlus. I'm thinking perhaps it's a mistake in the Uniden write-up, since DSDPlus usually gives way more information about a frequency than the scanner.

I'm not saying that DSDPlus cannot do it. The Fast Lane verisons can do many things. But I'm not sure if DSDPlus is programmed to provide an LCN finder feature at this time.

Basically [if DSDPlus supported this in the future] you would have to program a scanlist of frequencies into a file. Then you'd have to be able to tell DSDPlus that you were performing an LCN find. DSDPlus would have to monitor a control channel until it indicates voice trafffic on an LCN. Then DSDPlus would have to quickly instruct the SDR device to switch through all of the frequencies listed in the text file and attempt to find a DMR signal that could be related to that trunked system/site. And of course it would have to check the control channel regularly (even if it is currently searching / stopped on a possible voice channel).

So I'm not saying it could not be done, but I don't think DSDPlus does it currently. And I'm thinking there are probably numerous ways that logic could be programmed in. The difficulty would be that as soon as some sort of LCN finding functionality is programmed into DSDPlus for one type of system [let's say Con+], you'll suddenly have everybody and their mother pushing the author to then add that functionality for Cap+ and any other type of system that uses LCNs and relies upon being preprogrammed with the LCN<-->frequency mapping.

So in my mind it is best to just use DSDPlus and a scanner to accomplish this. If you've listened to raw DMR for even a short while, it's very easy for your ears to tell what a DMR voice channel sounds like.

Mike
 
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Gilligan

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We use a statistical correlation of channel grants/updates vs active frequencies. It is not a mistake.
I was thinking it was something like that but wasn't sure since statistical analysis can never be confirmed as 100% correct. Either way, if it gets the job done, that's great. I will try using the LCN finder again for Connect Plus on my BCD436HP and see if I can get it working again.

I agree with mtindor that it would be a challenge for DSDPlus to incorporate this capability since it seems like a lot of back and forth comms between FMP24 and DSDPlus, but I'm sure it could be implemented at a future time and would definitely be a huge help.
 

slicerwizard

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I don't understand how Uniden can advertise this capability and yet it isn't possible in DSDPlus.
Programs do what the coders put in them. If they didn't put it in, the program won't do it. Might as well also ask why DSD+ doesn't support Phase II. BTW, I don't see an LCN finder feature as that big of a deal. It's not that hard to manually compare what's being broadcast on the control channel vs what's showing up on each known voice channel. What would impress me is an RF channel and LCN finder. Manually finding trunk voice channels, especially in crowded urban spectrums, can be a pain. Control/rest channels are easy to find - give me a way to tell the scanner or decoder to go find the voice channels (and their LCNs) that go with that NXDN or DMR control/rest channel I just found. It shouldn't be hard - just find the RF channels that are using the same protocol and are carrying the same talkgroups that the control/rest channel is announcing.
 
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DaveNF2G

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That is where the FCC database becomes useful. You can narrow your voice channel survey to frequencies licensed to the same entity that owns the control channel.
 

mtindor

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It shouldn't be hard - just find the RF channels that are using the same protocol and are carrying the same talkgroups that the control/rest channel is announcing.

It shouldn't be hard, except for many systems out there like the ones in my area (even wide area CON+) are mostly vacant. No traffic / channel grants, and it becomes a bit more difficult to do that.

In the absence of "busy" systems, the brain, DSPlus and a second scanner with voice frequencies from licenses programmed in goes a long way.

Incidentally, PA/OH people are missing opportunities the past few days/mornings. VHF tropo was excellent the past two days, during most of the day and at night here in Ohio. UHF tropo was great over into PA both nights from Ohio. That damned tropo will get you though, when you are trying to figure out systems outside of the local area.

Mike
 

slicerwizard

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That is where the FCC database becomes useful. You can narrow your voice channel survey to frequencies licensed to the same entity that owns the control channel.
There are many systems where that doesn't work. Those who've had to deal with them can chime in if they want.


It shouldn't be hard, except for many systems out there like the ones in my area (even wide area CON+) are mostly vacant. No traffic / channel grants, and it becomes a bit more difficult to do that.

In the absence of "busy" systems, the brain, DSPlus and a second scanner with voice frequencies from licenses programmed in goes a long way.
I've run into that here as well. With Con+, the voice channels seem to wake up every minute or so to do a repeater test. When they do, they broadcast their NID and site number, so again, an automatic hunt for those RF channels would be nice. It doesn't get you LCNs, but it's a start.
 

mtindor

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That is where the FCC database becomes useful. You can narrow your voice channel survey to frequencies licensed to the same entity that owns the control channel.

You sometimes have to be real savvy. Sometimes multiple licensees are involved in a system. PADRN comes to mind. Sometimes there are numerous FRNs bearing different ownership names but related in nature, and if you don't know that the FRNs are related you never know to look at the additional frequencies. Oh, and people shouldn't be mislead by lack of proper emissions on the license, nor should they disregard non-trunking licenses. Everything is fair game -- even expired licenses. Here in Ohio, for a long time it was quite common for a certain radio shop to use frequencies that had licenses that had been expired for 6+ years.

Then, just when you think it is safe to go in the water, part 22 rears its ugly head and you find one or more active frequencies on one or more sites being in the VHF / UHF paging spectrum and then usually have no way to actually pin down the location of a site short of following the signal until you pinpoint the location.

I rely heavily on the FCC database, no doubt about it. But it's not the holy grail.

If one wants to get serious [and anybody who has went through the trouble of buying SDR stuff / antennas / etc should get serious], you actually need to scan the spectrum on a regular basis. Some [ok, the majority] of people get data from the DB and program their scanners and never realize how much there is out there, in their area, that has not been documented / discovered all because people are too lazy to run searches across the full spectrum.

Mike
 
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