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.