Determining DMR info for monitoring?

[KA2ZEY]

Now that I have a CS700 for DMR Ham, the other benefit is that I can finally monitor some local DMR business frequencies w/o using my computer. I've programmed in a few in the CS700 with the software. I've used a combination of SDR#, DMRDecode and DSD+ to find the color code. The part I don't quite understand is the group call number. I already have the DMR-MARC contact list programmed in (1,2,3,4). What info do I need to listen to the Business DMR transmissions besides the color code? I can hear some of them on my CS700 but not all. I'm guessing I'm missing some information on some? I've also tried both time slots.

I notice that DMRDecode will display group ### to group ### when there is a voice call down at the bottom.

 

[EricCottrell]

Hello,

Three things are needed, color code, time slot, and talk group.

Each repeater has two time slots. They can be treated like separate channels with two groups of users, or like a pseudo-trunk where users can use time slot one or time slot two.

Talk groups work similarly to trunked systems. You could consider a repeater to be a single channel or dual channel trunked system.

A lot of users in my area use defaults (Color Code 1, TS1, Talkgroup 1). Some users use the all-call (broadcast) talkgroup 16777215.

73 Eric

 

[SCPD]

What you will really need to do is listen for a while on DMRdecode, and note down all the talkgroups in use on the channels you want to listen to. Then, put them into the radio as group calls, and don't forget to add them to a group list. Then assign this group list to the channels.
If there are too many groups, you can use separate group lists e.g. one group list per frequency, or even per slot.
I don't know if the CS700 has an "RX only" checkbox in the channel parameters, but if it does, you may wish to make sure it is filled in, just to be safe.

 

[KE5MC]

Eric,
Naive question. Does the all-call work to hear leaser number groups or still treated as unique all-call group to all-call group used when a leaser number has not been defined?

bben95,
Yes, there is a Receive-only check box at the channel level data.

Hello,

snip..

Some users use the all-call (broadcast) talkgroup 16777215.

73 Eric

 

[SCPD]

Hope you don't mind if I answer instead of Eric.
The all call doesn't allow you to listen to all other groups. In fact, it doesn't allow you to listen at all. Everyone hears an all call, even without having it programmed in to the radio. The all call contact is transmit only, and does not allow you to hear any other groups/all groups.

 

[KE5MC]

No problem here about who answers the question. Just looking to sort out the details and how they work. Lots of info about what its 'called', what you can change it 'too'. Little on what it all means.

Thanks, bben95

P.S. Thinking again! Sounds like it would be what you would use for an emergency mode activated situation.

Hope you don't mind if I answer instead of Eric.
The all call doesn't allow you to listen to all other groups. In fact, it doesn't allow you to listen at all. Everyone hears an all call, even without having it programmed in to the radio. The all call contact is transmit only, and does not allow you to hear any other groups/all groups.

 

[Forts]

In a nutshell, to monitor *any* DMR user (ham or otherwise) you need: frequency, timeslot, group code and color code. If they are not using any sort of encryption you are good to go.

 

[WA0CBW]

Unlike analog where in the monitor mode you hear everything on the frequency in the digital mode you only hear if you have the correct time slot, color code, and talk group ID. There isn't really a monitor (all)-mode.

 

[SCPD]

Is it possible for a user to only use time slot and color code? and not utilize the talkgroup function? my police just went DMR from analog so I'd like to be able to continue monitoring them. They use XPR 7550 VHF. Also, apparently the coverage is so good, they decided to save money and just use portables. Kind of like how Cincinnati, Chicago, New York City do... they don't have mobile radios installed.

 

[SCPD]

No, it's not possible to use only timeslot and colour code. They have to use a group/s as well.
You can find the groups they are using with DMRdecode, and a RTL SDR if you don't have a discriminator tapped scanner. The RTL SDR is the cheapest way to go about it.
Systems who don't have any need to use the groups still have to use them, so usually they will just pick a group number and have all radios programmed for that one group.