CAP+ DMR System Question

[kruser]

How does a Capacity+ system tell the radios what channel to steer too when a repeater is about to drop and the current conversation comes up on a new frequency?

I know with a true P25 System that that info is transmitted in the data stream as well as a database of active voice channels.

I'm just curious how this is done on a CAP+ TRBO system.
I would assume the info is transmitted by channel number being as CAP+ systems do not rely upon LCN's in the same fashion as LTR systems or Connect + systems do.
In fact, I don't think CAP+ systems rely upon LCN's at all but probably rely upon the actual channel number.
I'd also suspect they may broadcast channel numbers somehow being as TRBO systems are found on VHF and UHF frequencies where there may not be channel numbers associated with actual frequencies like we have in the 700 and higher bands.

It sure would be nice if CAP+ systems also broadcast all possible voice channels or frequencies as well!

How about a CWID broadcast, is that broadcast in a digital format like a P25 system or do they send that in analog on an unused channel?

I've never really studied much about TRBO systems and how they work being as it required more work to receive them using DSD or something similar.
Now that scanners are coming out with TRBO capabilities, it would be nice to understand how these systems work.

Thanks for any info or links anyone may be able to provide.

 

[Voyager]

It is conveyed via the Rest Channel. (that's the pulsing channel which will rotate among the system frequencies)

All radios will tune there once they are done monitoring the active channel.

 

[adcockfred]

these rotating pulse freqs you talk of? will that make the freqs change or shift or inter change? my 2 or 3 cap and con systems that run in the low 490"s when I bring them up on sharp they all seem to staying in one place. but there're 2 or 3 diff wave forms

 

[kruser]

It is conveyed via the Rest Channel. (that's the pulsing channel which will rotate among the system frequencies)

All radios will tune there once they are done monitoring the active channel.

That makes sense.
For this particular system, the Rest Channel seems to stay on a certain frequency say 80% of the time before it will finally go silent and then can be heard on one of the other listed frequencies for the licensee.

Just a close guess, it seems to send out a burst of data every 1.25 to 1.75 seconds that lasts about .25 to .50 seconds reach burst unless the channel becomes active for voice traffic.
I guess that short burst of data contains enough info to make the subscriber radios work.

If the Rest Channel does become a voice channel, the Rest channel data can be heard almost immediately on another unused channel for other users that may need to bring up a repeater.
It seems to work well.

Now I need to search and see if there is a program that will display the Rest channel data. That could be handy info for setting up a CAP+ system where all the frequencies are not known.

Thanks for the info!

 

[adcockfred]

Well that is where I started in the FCC for all the freqs. for each player say 3 big one here. sothey know witch sys are being abandoned. and run on those freqs for a while my dump freqs is .2125 Every weekend they change something. our big p-25 change was when tier3 went to simulecast. we have a cap sys here with range of 800 miles

 

[kruser]

Well that is where I started in the FCC for all the freqs. for each player say 3 big one here. sothey know witch sys are being abandoned. and run on those freqs for a while my dump freqs is .2125 Every weekend they change something. our big p-25 change was when tier3 went to simulecast. we have a cap sys here with range of 800 miles

Did you know Mr. Mahoney?

edit: I've not used my SDR Stick in ages and then I only followed aircraft so I can't help with those questions.
I did mess with it for a few hours one day years ago and it could have been Monsanto or Pfizer as I needed a local P25 signal with good signal.
I was still using that tiny antenna they give you with the SDR Sticks!
I can't recall if Monsanto or Pfizer had any P25 on the air back then though. Ameren was EDACS and all I wanted to do was try my luck at decoding a P25 signal with the SDR dongle. It worked quite well actually using DSD and DSD was not very well developed back then.
You had to run it under Linux as there were no Windows versions yet.
After I confirmed I could use it for P25, I went back to monitoring aircraft and never did any more with it.

 

[adcockfred]

No that name doesn't ring a bell. Who was he with? I have a couple retirees that were n at the time of the old Houston system when it was on the tower in the gallieria. I re member being up there a couple times.

 

[garys]

The rest channel does not rotate in all systems. I have been monitoring one where the same frequency is always the default Rest Channel. If both OTA channels on that frequency are busy, the system will change to another frequency.

It is conveyed via the Rest Channel. (that's the pulsing channel which will rotate among the system frequencies)

All radios will tune there once they are done monitoring the active channel.

 

[garys]

DSD+ displays the Rest Channel data, but it usually takes a few minutes for it to figure it out. The less busy the system is, the longer it takes.

That makes sense.
For this particular system, the Rest Channel seems to stay on a certain frequency say 80% of the time before it will finally go silent and then can be heard on one of the other listed frequencies for the licensee.

Just a close guess, it seems to send out a burst of data every 1.25 to 1.75 seconds that lasts about .25 to .50 seconds reach burst unless the channel becomes active for voice traffic.
I guess that short burst of data contains enough info to make the subscriber radios work.

If the Rest Channel does become a voice channel, the Rest channel data can be heard almost immediately on another unused channel for other users that may need to bring up a repeater.
It seems to work well.

Now I need to search and see if there is a program that will display the Rest channel data. That could be handy info for setting up a CAP+ system where all the frequencies are not known.

Thanks for the info!

 

[EricCottrell]

Hello,

DMR voice transmissions have voice headers and terminators like P25, so there is a data stream before and after a transmission.

Capacity Plus systems have data messages the radios on the system use to determine what frequency and slot, i.e. channel, to use or monitor. The rest channel is the channel radios monitor while the radio is not receiving or transmitting on a talkgroup. The data on the rest channel is sent in short busts.

When a radio transmits, the rest channel becomes the voice channel for the talkgroup the radio is using, and another rest channel is assigned. The radios monitoring the talkgroup stay on the channel and receive the transmission. The radios monitoring other talkgroups move to the rest channel. When the transmission is over, the first batch of radios on the voice channel move to the current rest channel.

When only one talkgroup is active, the rest channel and active channel stay on the same frequency. They swap slots on each voice transmission. For example, if the rest channel is four on a transmission, the voice channel will be four and the rest channel will change to three. On the next transmission, the voice channel will be three and the rest channel with change to four.

When two or more talkgroups become active, then the rest channel will move to another frequency.

So when the system is not very busy, the voice transmissions and the rest channel will remain on the same frequency.

73 Eric

 

[kruser]

Mahoney was the CEO of Monsanto back in the day.
I took your post that you may or did work for them and may have known him.

Mahoney was a very private guy. He would have business meetings away from the Monsanto headquarters where he probably had super secure meeting rooms and instead, he would hold these meetings at local country clubs he was a member of.
He'd send in a security team with tons of RF sniffing equipment and scan your entire building for hidden bugs. We also had to key up every radio we may use on the day he held these meeting so they could capture the RF footprint of every radio we used.
Each radio has a slightly different 'fingerprint' than the next so they would program ours into their equipment as safe radios. If a local signal came on the air that did not have a matching fingerprint, the security team would stop the meeting until they could investigate the source.
In some cases, the security team would sniff the building the afternoon before the meeting day. Then they would actually stay overnight above and below the room the meeting was in.
They had tons of money invested in RF sniffing equipment.
Probably better than the NSA had or whatever 3 letter agency did that kind of thing back in the mid 80's.

I got to know the security team guys fairly well over the years.
They needed about 20 feet of table length to set all their equipment up!

The main things I can recall were lots of spectrum analyzers and service monitors and scopes for watching certain radio's IF output. And of course a ton of handheld RF sniffing devices.

We never had many problems where I worked where they had to halt the meeting. On the few occasions they did, it was almost always a delivery company calling in and letting his dispatcher know where he was.

Most of these secure meetings were to cut down on industrial espionage but I always suspected they were discussing other things like Agent Orange or some other really bad chemical that was probably banned.
We did get a lot of free AstroTurf from him! It held up well in staircase's where members would climb the stairs with the old steel spiked golf shoes.
Mahoney would not let the clubs publish his home address or work phone numbers in the clubs roster books. Basically just his name and what year he became a member.
When it came to billing time, they would get his address info out of the safe and later when we finally installed a computer system, it could pull up his mailing address.
He seemed to be a very worried man like someone was out to get him.
I'd hate to live like that carrying around that worry all day and night.
His security team was armed or they would bring in members of the FBI to provide gun security for him.

You could spot those guys a mile away with their dark sunglasses and coily cords coming out of their ears for their communication amongst themselves!

 

[kruser]

Hello,


So when the system is not very busy, the voice transmissions and the rest channel will remain on the same frequency.

73 Eric

Thanks for the detailed response Eric.
That helped me understand these system much more.

It also explains why the Rest Channel did not move around much through the night as the only users where several security guards so the system was very lightly loaded.

When the Rest channel did change, it was usually when another TG would become active while security was talking.
I know one of the other TGs I heard sort of often appeared to be workers in the Plant Science's building.
I guess some of those guys work day and night watching plants grow.
That division is housed in a pretty neat and very large building with lots of solar panels on the roof and a TON of windows for letting natural sunlight in. I don't know if the solar panels are for power generation or possibly heating water.
I'm sure they have a pretty high demand for electrical power and water being one of their main plant sciences labs. I've never driven by the building at night to see how much artificial light they may use but I bet it's a fair amount. The building does not have an open roof so they lose several hours of natural sunlight each day. They also have greenhouses at the plant sciences building as well as some out at the old Pfizer drug lab that would get a full days worth of real sunlight.
I don't know if the old Pfizer location is used for plant sciences or its greenhouse's are used in the manufacturing or research of medical drugs.
I know it has pretty tight security as you see guards using mirrors to look under vehicles and trucks as they come and go.
The Pfizer location also has a Capacity Plus system with 8 or 9 channels.
It is tied in with their main headquarters Cap+ system.

 

[kruser]

One other thing I notice about both main locations is when I program all the frequencies into a standard conventional system and set the audio type to digital, most signals do report Cap+. Every so often though., the 536HP will show it is hearing plain DMR and display DMR.
I use an Icom R9000 to monitor the actual frequencies and can usually tell by the sound if the channel is being used by a Cap+ system or plain DMR.
You also lose the Rest channel for a while if a channel was used for plain DMR. You don't really lose the Rest channel, it just moves to another channel but usually moves back to what I consider its primary frequency after maybe 5 to 10 minutes even of there is no use of the system at all.

When a DMR radio appears on a channel that is usually CAP+, it uses the repeater like a standard single channel repeater would. So no LCNs come into play as the DMR channel stays on a single repeater and LCNs appear to be unused or ignored on CAP+ systems.

Is this normal that they would allow plain DMR radios on a CAP+ repeater channel?

Usually when a radio comes up on a CAP+ repeater in DMR mode, there is a color code detected and I can set that color code on the frequencies used by CAP+ so the CAP+ signals do not tie up the scanning of my conventional system.
It just seems odd that plain DMR radios are seen on channels used by TRBO CAP+ radios.
I'd guess the plain DMR radios have a pre-populated list of available frequencies and they just listen for an unused channel and key up that repeater when needed. The channel appears to stay in DMR mode for several minutes before CAP+ radios can use it again.
I've seen this happen on pretty much every CAP+ channel.
The users using DMR are not the same users heard when running in CAP+ mode either. They sound more like scientists that wear lab coats while the CAP+ users are mostly security as they read off their location and findings as they reach each security check point.

 

[adcockfred]

Kruser, yes sir I know of which you speak. I have been driving US 81 sense the 60' we are K-staters. the first time I saw the out door tables with tablecloths in K. C, I could surmise something was amiss from the normal. But also they paid a heavy price for success. Roundup came out and they went 7 years while a trait was added every year to the bean plant before it could be used. And we never had the good bean plant here in US until after W.W. II.

 

[KevinC]

Well that is where I started in the FCC for all the freqs. for each player say 3 big one here. sothey know witch sys are being abandoned. and run on those freqs for a while my dump freqs is .2125 Every weekend they change something. our big p-25 change was when tier3 went to simulecast. we have a cap sys here with range of 800 miles

What system is that???

 

[mancow]

Mahoney was the CEO of Monsanto back in the day.
I took your post that you may or did work for them and may have known him.

Mahoney was a very private guy. He would have business meetings away from the Monsanto headquarters where he probably had super secure meeting rooms and instead, he would hold these meetings at local country clubs he was a member of.
He'd send in a security team with tons of RF sniffing equipment and scan your entire building for hidden bugs. We also had to key up every radio we may use on the day he held these meeting so they could capture the RF footprint of every radio we used.
Each radio has a slightly different 'fingerprint' than the next so they would program ours into their equipment as safe radios. If a local signal came on the air that did not have a matching fingerprint, the security team would stop the meeting until they could investigate the source.
In some cases, the security team would sniff the building the afternoon before the meeting day. Then they would actually stay overnight above and below the room the meeting was in.
They had tons of money invested in RF sniffing equipment.
Probably better than the NSA had or whatever 3 letter agency did that kind of thing back in the mid 80's.

I got to know the security team guys fairly well over the years.
They needed about 20 feet of table length to set all their equipment up!

The main things I can recall were lots of spectrum analyzers and service monitors and scopes for watching certain radio's IF output. And of course a ton of handheld RF sniffing devices.

We never had many problems where I worked where they had to halt the meeting. On the few occasions they did, it was almost always a delivery company calling in and letting his dispatcher know where he was.

Most of these secure meetings were to cut down on industrial espionage but I always suspected they were discussing other things like Agent Orange or some other really bad chemical that was probably banned.
We did get a lot of free AstroTurf from him! It held up well in staircase's where members would climb the stairs with the old steel spiked golf shoes.
Mahoney would not let the clubs publish his home address or work phone numbers in the clubs roster books. Basically just his name and what year he became a member.
When it came to billing time, they would get his address info out of the safe and later when we finally installed a computer system, it could pull up his mailing address.
He seemed to be a very worried man like someone was out to get him.
I'd hate to live like that carrying around that worry all day and night.
His security team was armed or they would bring in members of the FBI to provide gun security for him.

You could spot those guys a mile away with their dark sunglasses and coily cords coming out of their ears for their communication amongst themselves!

Sounds like a crooked bastard.

 

[adcockfred]

Not much different than the S S. Remember your not to speak bad of mother or google. Remember when they came by your house to take a picture?