Confused About How To Figure Out LCNs

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CanesFan95

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How come when I run DSDPlus on a Capacity Plus trunking frequency, sometimes I'll see more than 2 different channel pairs on a single frequency. For example, this is on 462.4000 MHz in Tampa. It shows channels 3, 4, 5, and 6 that have been keyed up by talk groups. (Most of the time, it's either channel 5 or 6 in the Event Log.) So how do I tell what the LCN of this frequency is? Thanks.
 

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EricCottrell

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Hello,

If you were just sitting on the one frequency, then that frequency is Channel 5/6. The site will also send information on what other channels are busy occasionally.

I find a Capacity Plus system will sometimes send out long transmissions on non-rest channels indicating the current rest channel. If you tune into a brief transmission that occurs every couple of seconds, then the rest channel indication should be the frequency you are monitoring.

If only one talkgroup is active then the rest channel will stay on the same frequency. When two talkgroups get active, then the rest channel will move to another frequency. You need to search out the new frequency.

You can also match the Channel Activity talkgroups with the voice information. If you are on channel 5/6 and see TG 12 being assigned to channel 4, you should see a transmission from TG 12 on the frequency for channel 4.

73 Eric
 

CanesFan95

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I find a Capacity Plus system will sometimes send out long transmissions on non-rest channels indicating the current rest channel. If you tune into a brief transmission that occurs every couple of seconds, then the rest channel indication should be the frequency you are monitoring

So does that mean that even though the Channel Activity window has the word "Rest" lit up, the RF frequency I'm monitoring might NOT actually be where the rest channel is currently assigned?

And, is there any limit to how how the channel number can go? Is 7/8 the max?
 

slicerwizard

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How come when I run DSDPlus on a Capacity Plus trunking frequency, sometimes I'll see more than 2 different channel pairs on a single frequency.
Because you're seeing every channel that the rest channel announces.


So how do I tell what the LCN of this frequency is? Thanks.
The latest DSD+ (2.10) displays that information.


So does that mean that even though the Channel Activity window has the word "Rest" lit up, the RF frequency I'm monitoring might NOT actually be where the rest channel is currently assigned?
It's quite likely.


And, is there any limit to how how the channel number can go? Is 7/8 the max?
16 should be the limit.
 

natedawg1604

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Just another tip: Do not rely too heavily on ULS to find new/missing system frequencies! And, never assume you will find all frequencies associated with a particular system by pouring through all the FCC licenses of the apparent system owner. You might, or you might not (and it's easy to waste lots of time analyzing dozens or even hundreds of FCC licenses from a single system owner - I know from personal experience).

If you have a hardware scanner (or just SDR# with the scanner plugin), you can look for new DMR/Nexedge/IDAS etc. frequencies by scanning through the entire UHF or VHF bands in plain-old Analog NFM mode, and simply listen for the distinctive sound associated with the relevant protocol. DMR is probably the easiest to recognize - it's VERY annoying and sounds like a boat anchor. The other protocols also have distinctive audio characteristics. You can also use SDR# with DSD+ (don't specify any protocol flag), and just scroll around on different frequencies to find new systems, as well as any missing or otherwise unidentified frequencies associated with a particular system.
 

WX4JCW

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Just another tip: Do not rely too heavily on ULS to find new/missing system frequencies! And, never assume you will find all frequencies associated with a particular system by pouring through all the FCC licenses of the apparent system owner. You might, or you might not (and it's easy to waste lots of time analyzing dozens or even hundreds of FCC licenses from a single system owner - I know from personal experience).

If you have a hardware scanner (or just SDR# with the scanner plugin), you can look for new DMR/Nexedge/IDAS etc. frequencies by scanning through the entire UHF or VHF bands in plain-old Analog NFM mode, and simply listen for the distinctive sound associated with the relevant protocol. DMR is probably the easiest to recognize - it's VERY annoying and sounds like a boat anchor. The other protocols also have distinctive audio characteristics. You can also use SDR# with DSD+ (don't specify any protocol flag), and just scroll around on different frequencies to find new systems, as well as any missing or otherwise unidentified frequencies associated with a particular system.

also if you use an SDR with DSD+ and SDRSharp when you look at the waterfall you can quickly see a pattern the different systems make
 

CanesFan95

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If you have a hardware scanner (or just SDR# with the scanner plugin), you can look for new DMR/Nexedge/IDAS etc. frequencies by scanning through the entire UHF or VHF bands in plain-old Analog NFM mode, and simply listen for the distinctive sound associated with the relevant protocol. DMR is probably the easiest to recognize - it's VERY annoying and sounds like a boat anchor. The other protocols also have distinctive audio characteristics. You can also use SDR# with DSD+ (don't specify any protocol flag), and just scroll around on different frequencies to find new systems, as well as any missing or otherwise unidentified frequencies associated with a particular system.

That's exactly what I've been doing. I have several scanners with discriminator mods. The BCT-15X proved to have a weaker waveform for some reason, but the BC780XLT with the discriminator mod has a much bigger waveform. It's easier to just search from 460 - 465 MHz and 450 - 455 MHz and just find stuff. I do use the FCC search on RadioReference which helps immensely, but I know licensing data isn't foolproof.

And you're not kidding about what an obnoxious noise DMR is. It's hellacious and it interferes with other analog conventional frequencies in a bad way. We seem to have a lot of frequencies that are doubled and tripled up where you have multiple different agencies on the same frequency in the same county. Some are analog and some are MotoTRBO, and it's a mess.

There are times where you can hear the DMR bursts underneath an analog signal and it sounds like a nasty grunting sound. Prolly leaves mall security and drive through cashiers confused what that noise is. In the car I like to scan conventional analog business repeaters on the ham rig, but there's so much DMR noise and interference that you really have to program the PL encodes and decodes. Otherwise, the radio constantly stops on that hideous noise blaring out the speaker.

Well, I've been piecing together an Excel file to try and figure out some of the system in our area. It seams like we have a lot of small 2 and 3 frequency Cap+ systems all with RAS. I wish we could just have like 1 big system that has everyone on it instead. It seems like the Tampa area is plagued with lots of these small systems. It was the same way with LTR before DMR so rudely moved in. Lots of 1 or 2 frequency LTRs around. I just wish I really understood how Cap+ trunking works and can't seem to find anything online that really explains it.
 

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CanesFan95

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And, I'm guessing repeaters on the same system have to have the same color code. So that's one way to filter in Excel and start narrowing it down. If each radio has to be programmed with the color code, then as it trunks around, each repeater would have to have the same color code on the whole system. In fact, I think I just figured out my first system!
 

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CanesFan95

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If they don't all have the same color code, then would that mean a radio on one color code can't trunk around to frequencies on a different color code than what's programmed in the radio?
 

wx5uif

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Each frequency is programmed into the radio with the corresponding color code. When told to go to a certain freq/ slot the radio knows what color code it should have on the frequency.
 

CanesFan95

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So anyway, exactly what IS a color code? What does that mean and why does it matter?
 

EricCottrell

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Hello,

The Color Code is like PL or DCS, to prevent other users from accessing a repeater or interfering. I have one Connect Plus system that sets it to zero at all sites and another that sets it to the site number modulus 16. Most Capacity Plus and Connect Plus systems around me use the same color code for all frequencies at a site, but I would not depend on it. All the radios that use a site are programed with the frequency and color code of each repeater (Channel pair) at the site.

The Capacity Plus system will do a brief burst every couple of seconds on the rest channel. So if you hear it and DSDplus displays rest, then you have the channel pair. Other channels displayed gives you clues of other channels in the system. All the radios that are idle are listening to the rest channel.

What makes things a little complicated is the long, maybe 5 seconds plus, idle bursts. A rest channel is displayed but it is for another frequency. The radios know the frequencies at the site so they will move to the rest channel. I suspect this transmission is for straggler radios. Sometimes activity on other channels will be shown.

The system will allocate the rest channel to the next active talkgroup and move all the idle radios to another channel, the new rest channel. When the transmitting radio is finished, all the radio in the talkgroup will move to the current rest channel. If another radio transmits a response in the talkgroup, the current rest channel will become allocated to the talkgroup and a new rest channel will be allocated, if available.

As I mentioned before, if only one talkgroup is active at a time, the above action results in the talkgroup and the rest channel switching channels on the same frequency (1->2->1->2). This makes it difficult to figure out other channels. As soon as a second talkgroup is active, both channels on a frequency are active so the rest channel has to move to a channel on another frequency if available. It the system becomes moderately busy, the rest channel will tend to rotate up through all the channels.

It takes some work to piece systems together. I started by searching each band and making note of the frequency, color code, channel pair, and signal strength of bursts I heard. I also noted any active capacity plus channels and any channels displayed, but did not pin the channel pair to that frequency. Signal strength can be helpful as frequencies at the same site tend to be of similar signal strengths.

You need to search over time as the system will only send the brief burst only on one frequency at a time. So if you find brief bursts on Channels 1/2 on one frequency and Channels 3/4 on another frequency at the same time, then they are likely different systems. If the rest channel moves off of Channel 1/2 then search and see what frequency with Channels 3/4 becomes active. See if the same talkgroups appear on different channel pairs.

73 Eric
 

CanesFan95

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Thanks for the advice. I will prolly have to read it like 8 more times to really get it. But I do notice that seeing the same talk group and radio IDs moving to different frequencies is a clue. This is really hard...
 
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DaveNF2G

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I have only seen color code vary by site or system. However, YMMV, obviously.

It helps to have data on previously existing systems when they switch to DMR. Different licensees won't be swapping frequencies. So if it used to be ABC Communications' LTR system, then the new DMR system should also be ABC Communications and will generally use the same frequencies and sites.
 

CanesFan95

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Is it possible that a system can skip LCNs and just have no frequency? Like, can you have 1 system with a 3/4 frequency and a 5/6 frequency, but no 1/2 frequency?
 

slicerwizard

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I don't see why not. A system could have three repeaters with the first one manually disabled due to interference or some other reason - maybe it was a borrowed frequency and the lender wants it back. Just yank the power cord and it's gone - and the system keeps running.

I should add - there may be an option to set a repeater to "use last", i.e. only use if all other slots are in use. So there may be a 1/2 repeater, but you won't see it until the system is loaded up.
 
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