Questions about GATRRS/Austin P25

[RadeoZee]

So just to preface this, I'm a newbie in a large context here, so I apologize if I missed a post or am asking stupid questions here.

So, I've been playing around with DSDPlus and Unitrunker. I've got a dual dongle setup with two R820Ts, controlled by UniTrunker and piped out to DSDPlus via VAC. I've been monitoring things and trying to customize my setup within DSDPLus so it'll list the correct sites, groups, frequencies, etc. I've noticed some oddities that I can't reconcile.

1) Band plan for GATRRS lists 762.00625 as one of the bands, but apparently 763mhz is where it should start at. Is this a configuration issue with the P25 system? I've deleted the UniTrunker data I downloaded from here and it seems like the system is broadcasting that information, rather than it being a typo in the RR database.

2) I think the site 001-010 "Central Austin" has a different control channel now. The control channel detected by DSDPlus doesn't match with Unitrunker or any of the frequencies I've input. It reports a control channel of 5250. In UniTrunker, we have a CC of 01-1154 at 769.21875 mhz. I don't think that is the case anymore. In the past week, the alternative CCs for 001-010 have disappeared and it's just that one I listed. I have no idea what to make of this.

3) The way the DSDPLus.groups and DSDPlus.sites for GATRRS on here, is constructed doesn't seem to jive with the data I've been working with. For example, the Simulcast sites are listed as 001-001 001-002 but DSDPlus detects them as 1.1 and 1.2. It was easy enough to tweak the files, but wasn't sure if that discrepancy was a format thing between versions or if the GATRRS system has been undergoing changes.


If anyone could clarify these things, I would greatly appreciate it.

 

[nd5y]

1) That is normal. Unitrunker should get the band plans from the control channel data stream. The band plan frequency is kind of meaningless, that is just the lowest channel where the logical channel numbering starts. It doesn't necessarily mean that frequency is used on the system.

2) I can't help with that because I'm too far to receive the system and don't know that much about it. You can't always count on the frequencies in the RRDB to always be accurate.

3) That is probably normal. It probably shows RFSS.SITE instead of RFSS-SITE and drops the leading zeros but I have never used DSD+ with a dongle for trunking.

 

[RadeoZee]

I appreciate the clarification there. Thanks!

 

[motorola_otaku]

Someone local to ATX can correct me if I'm wrong but I believe the Central Austin 700 site is only used for Capitol Security and other DPS units working at the Capitol. If that's the case you should treat it as a separate system from the two Simulcasts and the IR sites.

Also, virtually every Motorola P25 system deployed in the US uses the same channel ID table (band plan.) 762.00625 is the correct base frequency.

 

[RadeoZee]

>Also, virtually every Motorola P25 system deployed in the US uses the same channel ID table (band plan.) 762.00625 is the correct base frequency.

That helps a lot. Thank you for that tid-bit.

 

[rbarker]

Simulcast 1 control channel is 851.2875 ; Simulcast 2 control channel is 851.1375 as of right now 9:18 am Wednesday; from what I have heard Capitol DPS which are the ones inside the capitol and the security for the state buildings are on the 700 Mhz tower. DPS units that do traffic police activity downtown are on the regular 800 System. I know it's confusing. But I have also heard some Austin police Narcotics activity on the 700 that was being simulcast from some of their regular 800 Mhz talkgroups. I dont regularly monitor the 700 tower so i don't know if anything might have changed lately. I have never heard any radio traffic on it however that is outside of the Capitol Complex (which includes state office buildings)

 

[RadeoZee]

I dont regularly monitor the 700 tower so i don't know if anything might have changed lately. I have never heard any radio traffic on it however that is outside of the Capitol Complex (which includes state office buildings)

I have seen some very, very limited traffic in Unitrunker for the 700 over the past week or so but it's one of the only sites that seems to actively deny a lot of radios more than anything else. I can't figure out where DSDPlus is pulling the control channel as 5250, since I can't find that anywhere on the whole GATRRS system at all. It's definitely a little odd ball.

 

[Project25_MASTR]

Simulcast 1 control channel is 851.2875 ; Simulcast 2 control channel is 851.1375 as of right now 9:18 am Wednesday; from what I have heard Capitol DPS which are the ones inside the capitol and the security for the state buildings are on the 700 Mhz tower. DPS units that do traffic police activity downtown are on the regular 800 System. I know it's confusing. But I have also heard some Austin police Narcotics activity on the 700 that was being simulcast from some of their regular 800 Mhz talkgroups. I dont regularly monitor the 700 tower so i don't know if anything might have changed lately. I have never heard any radio traffic on it however that is outside of the Capitol Complex (which includes state office buildings)

It's going to be interesting when A/T County Wide (Simulcast 1) and E620 (Simulcast 2) are merged along with the standalone "Intelli" sites.

Anyway, to help the OP out, the band plan is how the radio tracks the system. If the radio can't find an active control channel in it's preprogrammed list and the option is enabled, it'll begin to scan the channels according to the band plan until and active control channel is found with a matching WACN and System ID. The bandplan tells the radio where to go. Instead of the control channel saying TG: 01FE got to 851.3250 MHz it simply says TG: 01FE >1-0025 which is calculated based on the bandplan. I.E. 25 channels up from the base frequency on channel ID 1 which in the case of GATRRS is a base of 851.0125 MHz with 12.5 kHz channels and a -45 MHz transmit offset (25*0.0125+851.0125=851.3250 MHz, transmit at 806.3250 MHz).

For the casual observer, the bandplan is how your radio tracks the system. To actual subscribers on the system...it's the beauty of what makes P25 trunking tick (you can actually learn a lot just looking at control channel data) such as the system capabilities, adjacent sites, active control channels, encrypted talkgroups, pages (which in Williamson county are also used to remotely activate KNOX boxes for some gated neighborhoods), affiliations, etc.

 

[RadeoZee]

It's going to be interesting when A/T County Wide (Simulcast 1) and E620 (Simulcast 2) are merged along with the standalone "Intelli" sites.

Anyway, to help the OP out, the band plan is how the radio tracks the system. If the radio can't find an active control channel in it's preprogrammed list and the option is enabled, it'll begin to scan the channels according to the band plan until and active control channel is found with a matching WACN and System ID. The bandplan tells the radio where to go. Instead of the control channel saying TG: 01FE got to 851.3250 MHz it simply says TG: 01FE >1-0025 which is calculated based on the bandplan. I.E. 25 channels up from the base frequency on channel ID 1 which in the case of GATRRS is a base of 851.0125 MHz with 12.5 kHz channels and a -45 MHz transmit offset (25*0.0125+851.0125=851.3250 MHz, transmit at 806.3250 MHz).

For the casual observer, the bandplan is how your radio tracks the system. To actual subscribers on the system...it's the beauty of what makes P25 trunking tick (you can actually learn a lot just looking at control channel data) such as the system capabilities, adjacent sites, active control channels, encrypted talkgroups, pages (which in Williamson county are also used to remotely activate KNOX boxes for some gated neighborhoods), affiliations, etc.

Thank you for this explanation. I just kinda dove into Radio with both feet and am still figuring out how steep the learning curve is. Specifically, the reason my question about the band plan came up when I took a Uniden BCP325P2 for a test drive and during my attempts to load in the network, it kept complaining about the bandplan being incorrect. A deeper look shows that 762mhz was why FreeScan was complaining. According the FCC database, 762mhz is for "Low Power Auxiliary Service, and the Low Power Television (LPTV) Service (including TV Translator, TV Booster, and Class A Stations). Operation of unlicensed Part 15 devices is permitted between 698 and 763 MHz."

So my question is, why would the band plan start "outside" of the allotted frequency? I've noticed a lot of even numbers for various groupings of frequencies, so does that the system would need to start at 762mhz in order to allocate channels on 763mhz?

 

[Project25_MASTR]

It's simply the default 700 MHz band plan from Motorola. Want to see something really weird...look at how VHF band plans operate (even the VHF portions of GATRRS). The bandplans define unrealistic splits (since VHF and UHF is known as Other Band Trunking) which are only used to calculate where the SU should RX...TX information is updated live on per channel basis. To do this, look at an adjacent channel and then pull up the license on the FCC database...you'll note the bandplan split is nowhere near similar to what is actually licensed.

 

[RadeoZee]

Thank you very very much for your explanation.

 

[hiegtx]

Thank you very very much for your explanation.

Zee,
That "complaint" from FreeSCAN about the incorrect (or in some cases, missing) band plan is an error message you can ignore. It usually comes up a few times with any new programming file, then will, at some point, disappear. You may also, on occasion, see an error message stating that weather data is missing. That one can also be ignored. As already noted, on a P25 system, the band plan information needed is carried on the control channel data, and requires no action on your part.

 

[DanRollman]

It's going to be interesting when A/T County Wide (Simulcast 1) and E620 (Simulcast 2) are merged along with the standalone "Intelli" sites.

How is traffic currently split between Simulcast 1 and Simulcast 2? Do they completely overlap eachother, and is the split just for capacity reasons?

If so, that would be a lot like Simulcast A and Simulcast B on the PCWIN system in Tucson, Arizona (Pima County Wireless Integrated Network (PCWIN) Trunking System, Tucson, Arizona - Scanner Frequencies). All radios have both simulcasts available, but as you can see there we've been able to document which of the two identical simulcasts particular agencies are primarily on. This is important, since it means you know which simulcast to listen to for a particular agency you want to monitor.

Dan

 

[rbarker]

I'm not aware of the Simulcast 1 and Simulcast 2 in Austin merging. Simulcast 1 is mostly public safety including the jail, police, sheriff, EMS and fire. Simulcast 2 is mostly city and county agencies such as Road, trash, parking, Austin Energy, animal control, etc. It was my understanding that If the trunking were to go down, then the fail safe was that they would default to a single frequency but that has never happened. I know it's supposed to be fast but with more channels added it would seem like they may get occasional errors where they go to press their microphone to talk and get a buzz which means there are no frequencies available since all are being used. The Intelli sites are there in fringe areas where some of the regular towers do not reach. I was also told those are at a slower baud rate but not sure if that's still correct.

 

[hiegtx]

I'm not aware of the Simulcast 1 and Simulcast 2 in Austin merging. Simulcast 1 is mostly public safety including the jail, police, sheriff, EMS and fire. Simulcast 2 is mostly city and county agencies such as Road, trash, parking, Austin Energy, animal control, etc. It was my understanding that If the trunking were to go down, then the fail safe was that they would default to a single frequency but that has never happened. I know it's supposed to be fast but with more channels added it would seem like they may get occasional errors where they go to press their microphone to talk and get a buzz which means there are no frequencies available since all are being used. The Intelli sites are there in fringe areas where some of the regular towers do not reach. I was also told those are at a slower baud rate but not sure if that's still correct.

I think Dan may have been thinking of this previous post (earlier in this thread).

Questions about GATRRS/Austin P25

So just to preface this, I'm a newbie in a large context here, so I apologize if I missed a post or am asking stupid questions here. So, I've been playing around with DSDPlus and Unitrunker. I've got a dual dongle setup with two R820Ts, controlled by UniTrunker and piped out to DSDPlus via VAC...

forums.radioreference.com

I'm well out of the area, so I would not have any further details.

 

[Project25_MASTR]

How is traffic currently split between Simulcast 1 and Simulcast 2? Do they completely overlap eachother, and is the split just for capacity reasons?

If so, that would be a lot like Simulcast A and Simulcast B on the PCWIN system in Tucson, Arizona (Pima County Wireless Integrated Network (PCWIN) Trunking System, Tucson, Arizona - Scanner Frequencies). All radios have both simulcasts available, but as you can see there we've been able to document which of the two identical simulcasts particular agencies are primarily on. This is important, since it means you know which simulcast to listen to for a particular agency you want to monitor.

Dan

Some sites are co-located, some are not. The site alias for "Simulcast 1", is A/T County Wide. The site alias for "Simulcast 2" is E620. Some talkgroups are currently steered to a specific "site" while others are capable of utilizing whichever currently provides the best coverage.

I'm not aware of the Simulcast 1 and Simulcast 2 in Austin merging. Simulcast 1 is mostly public safety including the jail, police, sheriff, EMS and fire. Simulcast 2 is mostly city and county agencies such as Road, trash, parking, Austin Energy, animal control, etc. It was my understanding that If the trunking were to go down, then the fail safe was that they would default to a single frequency but that has never happened. I know it's supposed to be fast but with more channels added it would seem like they may get occasional errors where they go to press their microphone to talk and get a buzz which means there are no frequencies available since all are being used. The Intelli sites are there in fringe areas where some of the regular towers do not reach. I was also told those are at a slower baud rate but not sure if that's still correct.

The reason for dual layering of simulcast systems is one of capacity. Many P25 systems (especially the earlier ones) were bound by the limitations of a T1 circuit (these are known as circuit switched systems as they use traditional telco switching techniques). Basically, the control functions of simulcast required four of the 24 timeslots which left 20 available to support the physical repeater channels which put a hard limit of 20 channels on a simulcast "site". Now with the transition to IP, that limit has been expanded to 28 channels if my memory serves correctly. Now, in terms of trunking theory, each repeater added to a site increases the call handling capability exponentially.Two stacked systems only provided the capacity of the number of channels by 2 where one system with 3 or 4 more channels can handle 4 times as much. Think of 2^4+2^4=32 versus 2^6=64 (not quite that simple in expansion though).

I'll also note, Intelli site referrers to a standalone, non-simulcast site to CoA. Intelli sites are actually what standalone sites used to be called in Type II trunking as one of the "features" of the Motorola Quantar repeater was that it had the ability to be a trunking site controller. Astro 25 does not have this ability and requires a site controller be present. All of the Intelli sites are full blown P25 trunking at 9600 bps but used to be older Type II sites. Also, the newer releases of Astro 25 no longer support the Quantar and last I heard, the city had actually gotten everything upgraded to GTR8000's in preparation for the merger of the simulcast system but my understanding is that the Permian Basin merger Middle Rio Grande portion of the system has introduced some delays into the initial planning.

 

[motorola_otaku]

Some sites are co-located, some are not. The site alias for "Simulcast 1", is A/T County Wide. The site alias for "Simulcast 2" is E620. Some talkgroups are currently steered to a specific "site" while others are capable of utilizing whichever currently provides the best coverage.

In the early days of the system "E620" stood for "east of FM 620" and was only supposed to provide city limits coverage for public works users, though I'm sure things have probably changed somewhat in the last 16 years.

This was the original site map: File:Austin.jpg - The RadioReference Wiki

The IR sites were never Type II and I think some of OP's confusion about "baud rates" came from early discussions about the simulcasts using LSM/CQPSK while the IR sites ran C4FM (and were the only sites early P25 9600 scanners i.e. the 796T could track.)

 

[KTR722]

In regards to LE/FD/EMS traffic, I have found Simulcast 1 (CW) is generally the preferred site to monitor. *Currently*, most of the primary Police/Fire/EMS is also being carried on Simulcast 2 (E620). That is not always the case however. CTECC has the ability to shift TGIDs between sites on the fly depending on radio load and other factors. Some examples: 1) About a year ago, for whatever reason, all of the EMS traffic except MCOM S was also on Simulcast 2. 2) Currently all of the ESD TGIDs are only on Simulcast 1 but not also on Simulcast 2. Given where I live (close to Lake Travis), I generally monitor Simulcast 2 since the signal quality is better so I am more attuned to seeing TGIDs being added and dropped off E620.

In any case, your best bet is to monitor both sites initially and get a good feel on where most TGIDs you want to monitor currently reside. If you dont hear a TGID that your are looking for on one of the sites, be sure to check the other site. Using some logging software such as ProScan will also give you a good idea if any of the TGIDs you are looking to monitor are currently being simulcasted on both sites or just on one site.

 

[garys]

This, along with a couple of the other posts in this thread, has cleared this up for me. Since I only get to Austin about once a year, I've had a hard time sorting this out. I'm up in the 69000 area of Research and have been having trouble getting reliable coverage. Setting Simulcast 2 to "Avoid" has helped that quite a bit.

It's a busy traffic accident day in Austin, so AFD is very busy dispatching both city and county units.

For once, I'm also getting the Bastrop Simulcast pretty well too. .

Thanks for the clarification.

In regards to LE/FD/EMS traffic, I have found Simulcast 1 (CW) is generally the preferred site to monitor. *Currently*, most of the primary Police/Fire/EMS is also being carried on Simulcast 2 (E620). That is not always the case however. CTECC has the ability to shift TGIDs between sites on the fly depending on radio load and other factors. Some examples: 1) About a year ago, for whatever reason, all of the EMS traffic except MCOM S was also on Simulcast 2. 2) Currently all of the ESD TGIDs are only on Simulcast 1 but not also on Simulcast 2. Given where I live (close to Lake Travis), I generally monitor Simulcast 2 since the signal quality is better so I am more attuned to seeing TGIDs being added and dropped off E620.

In any case, your best bet is to monitor both sites initially and get a good feel on where most TGIDs you want to monitor currently reside. If you dont hear a TGID that your are looking for on one of the sites, be sure to check the other site. Using some logging software such as ProScan will also give you a good idea if any of the TGIDs you are looking to monitor are currently being simulcasted on both sites or just on one site.

 

[KI5IRE]

I have a few questions about this system, what sites are the Police, Fire, EMS talkgroups on for Austin/Travis County and TxDPS in Austin and at the Capitol?

Also, what are the "IR" sites?