Batboard

I've just started to get interested in DMR and MotoTRBO. I'm trying to make sense of Capacity Plus. I've come to think of it as vaguely like LTR, with the 'rest channel' with periodic data bursts. (I understand it's not actually the same as LTR; it's just the best analogy I've found.)

I'm having a hard time learning exactly how it works, though. In a single-frequency setup, does it still support two voice slots, or does the control signaling require a slot to be kept open? (Is a single-frequency Capacity Plus system even valid?)

Motorola also says that Capacity Plus supports "as many as 1,200 radio users." Where does that limit come from? Is it an actual hard limit from something, or estimated based on channel capacity or something? (This is purely academic; I have no intention of setting up a 1200-radio repeater, and certainly not on one frequency!)

Yes, a single repeater Capacity Plus system is viable. Most of ours are single repeater.

Just as you suggested. a single repeater Capacity Plus is somewhat similar to a 2 channel LTR site. It supports 2 simultaneous voice conversations. No dedicated control channel.

As far as capacity, it all depends on how much people talk. I have a single repeater capacity Plus (2 time slots) with 175 radios on it with little busies and another with 30 radios and constant complaints of busies.

RFguy wrote:Yes, a single repeater Capacity Plus system is viable. Most of ours are single repeater.

Just as you suggested. a single repeater Capacity Plus is somewhat similar to a 2 channel LTR site. It supports 2 simultaneous voice conversations. No dedicated control channel.

Thanks! I suspected that was the case, but couldn't find it confirmed anywhere. Had a fear I'd set this up to tinker with and find that the second slot couldn't be used because of the occasional beacon there or some nonsense. Glad that's not the case.

RFguy wrote:As far as capacity, it all depends on how much people talk. I have a single repeater capacity Plus (2 time slots) with 175 radios on it with little busies and another with 30 radios and constant complaints of busies.

I'm mostly wondering where this number came from, and whether it was a ballpark estimate someone in marketing at Motorola came up with, or if there's an actual limit somewhere, e.g., a maximum radio ID of 1200. Does Capacity Plus even have a notion of a user/radio/subscriber ID, or is it all TG-based like LTR?

Obviously I need to buy some gear and start playing.

A Capacity Plus system can have a maximum of 6 repeaters, which gives you 12 talk paths.

I looked in the system planner and it looks like they are using a maximum of 100 radios per talk path, so that's where the "up to 1,200" users comes from. You in fact can have far more (or less) than that depending on the users usage patterns.

The 100 users per channel has been an FCC / Industry Canada trunking system design guideline forever. Basically, if you want more channels, you should have more than that many users before they will consider granting an additional frequency pair. If it's a public safety system, they may relax the guideline & go with 50-75 users per channel. As RF Guy says, what users experience in reality have little to do with total subscriber numbers. It's far more affected by how many distinct user groups (talkgroups) are being used on a regular basis. You can have 1000 radios, if they are all on the same talkgroup, there are no capacity issues on a single repeater. Split those users into 20 talkgroups, now you need those 10 channels/slots!

RFguy wrote:A Capacity Plus system can have a maximum of 6 repeaters, which gives you 12 talk paths...

I had read that they can have a maximum of 8 frequencies for a total of 16 talk paths. Now I have to do some more research to see which is accurate.

Jim1348 wrote:

RFguy wrote:A Capacity Plus system can have a maximum of 6 repeaters, which gives you 12 talk paths...

I had read that they can have a maximum of 8 frequencies for a total of 16 talk paths. Now I have to do some more research to see which is accurate.

The planning Guide indicates "maximum of eight Trunked Repeaters (16 logical channels) at a site". But goes on to indicate "For the Data Revert Repeaters at a site, up to eleven Revert Repeaters (22 logical channels) can be supported.However, the number of Trunked Repeaters plus the number of Data Revert Repeaters must not exceed a total of 12. For example, if there are eight Trunked Repeaters at a site, only up to four Data Revert Repeaters
can be supported at that site."

Hope that helps --

Thanks for the update. I was looking at an older system planner.

Apparently, prior to R02.30.00, Capacity Plus Single Site allowed up to 6 trunked repeaters (12 logical channels) and twelve Data Revert repeaters (24 logical channels).

From software version R02.30.00 up to 8 trunked repeaters (16 logical channels) and twelve Data Revert Repeaters (24 logical channels) are allowed.