DMR System & alternating Color Codes

[natedawg1604]

Hi there,

In DSD+ I've been tracking a UHF frequency that registers as type "DMR", and the Color Code alternates between 1 and 7. While the Color Code changes between 1 and 7, I can hear/watch people talking and it sounds like the same individuals using the same talkgroup. Notably, when the Color Code changes the slot and channel remain constant. Based on comments made by radio users, it seems the subscriber radios have at least two channels.

In DSD+ the channel activity window never shows more than one channel active at a time, and it's never displayed 3 or more channels. I'm not seeing error messages, so I don't think I'm getting interference between two systems. Has anyone encountered any DMR systems (whether conventional or trunked) that change color codes like this within the same system?

 

[Forts]

Can you make a recording and post it somewhere? Just hit R in DSD+ and let it run for a bit during some voice activity. How's your signal quality? The only time I usually see oddities with color code is with weak signal or two overlapping systems on the same frequency.

 

[sm0vec]

The colour code shouldn't be able to change on the same site and frequency. The most likely is that it's overlapping systems on the same frequency. I've seen this quite many times, and even really bad cases where the overlapping systems are using the same colour code and talkgroups, which means that they sometimes might hear eachother (in this case, one system is an indoor system, but still it's a risk for overhearing).

One question though, what kind of radio do you use? If you are using a physical radio with discriminator output it's a possibility that you are listening to a frequency in between two frequencies on the same site of a Capacity+ system. This would explain that it's the same users that you are hearing.

As an example; if the system have two frequencies 420,00625 (CC1) and 420,01875 (CC7), but your radio is set to 420,0125, then you will for sure with most scanner-type radios get the traffic from both frequencies when the active channel changes.

However, in a Capacity+ system when jumping between channels, you should at least have seen 4 channels in the channel window.

 

[natedawg1604]

Well I think I solved the puzzle; I happened to find two conventional DMR repeaters on adjacent UHF frequencies, and my dongle was getting co-channel interference. I don't get great reception from either repeater, so that only added to the confusion.

Previously I'd been using the "standard" 12.5 Khz step size for these UHF freqs. However, in SDR# I just changed the step size to 6.25 Khz, and it seems to have eliminated the Co-channel interference! Way cool.