Toronto Transit Commission - PowerTrunk TETRA

[EricCottrell]

View attachment 96400

Something else I've recently noticed... The Main & Current control channel frequencies are separate on Greenwood & Finch, but Birchmount & Malvern are still single, and the control channel takes up a time slot.

Hello,

The GSSI and ISSI information is sent along with the audio on any active timeslot. The Main frequency is the only one with a control channel. The result is you only see information on the Current frequency for Greenwood and Finch.

I can give an example using the image in your Sep 17, 2020 post. If the Current frequency was 937, you would only see Timeslot 1 active from GSSI 102723. You see the whole site because you are monitoring 933.

You are missing activity on Greenwood and Finch as the activity on the Current frequency is likely due to all the timeslots on the Main frequency being active.

73 Eric

 

[HiVolt]

Actually if I click on the green Main frequency, it changes Main & Current to be the same. But I don't get any traffic at all then.

 

[EricCottrell]

Hello,

That is interesting. I find TETRA an interesting system as the systems I have monitored keep all the site frequencies active. I would think that it would only keep the Main frequency with the control channel active when there is no activity, but maybe it is a method for roaming radios to quickly find the Main frequency.

DMR capacity plus systems will alternate between time slots on a frequency when only one talkgroup is active and you need two active talkgroups at the same time for the rest channel to switch to another frequency. This makes it difficult to scope out a lightly used Capacity Plus system. Since all the frequencies are active at a TETRA site, the controller may keep allocating timeslots on the last used frequency when the site is lightly loaded.

Current is always the frequency you are tuned to. Main just indicates the frequency containing the main control channel for the site.

73 Eric

 

[HiVolt]

Yeah, TETRA is a weird beast. Here's a screenshot of two talkgroups that are simulcast across all towers, working perfectly in this configuration.

There's not enough TETRA here in North America for local knowledge.

But this configuration changed recently on two of the towers that I can monitor, so maybe its still evolving.

 

[Andy_SDS100]

I'd like to hear what it sounds like as I can't hear it when I'm in Toronto as my scanner doesn't monitor TETRA.

 

[Enjoi19]

I'd like to hear what it sounds like as I can't hear it when I'm in Toronto as my scanner doesn't monitor TETRA

There’s an online feed of a few channels here: Toronto Transit Control Live Audio Feed

 

[HiVolt]

Yeah that's my feed, hehe. When the TTC shut off the analog scanner frequencies, it also killed the previous analog stream someone was running.

Then I stumbled upon this thread, and a week later or so had the stream up. Kinda a blessing in disguise, cuz there's way more stuff to listen to on this system than there ever was on the analog.

Downside is, no easy or cheap way to monitor live on the go. I have seen mobile two way TETRA radios for sale, but I havent found anything that includes standalone software and programming capabilities. I don't want a two way radio either, cuz thats not my intention, just to listen.

 

[HiVolt]

Few updates... Events channels were renamed to Incident channels.

102719 - Incidents Ch.1 - Used by Subway Superindentent
102720 - Incidents Ch.2 - Other incidents
102721 - Incidents Ch.3 - Shuttle Bus coordination

Few more stray Line 2 train TG's

100287 - Run 287
100290 - Run 290
100291 - Run 291
100296 - Run 296

Line 1 TG's

100187 - Run 187

 

[HiVolt]

Has anyone noticed a change on some towers? I Noticed on Greenwood & Finch this morning, seems 3 timeslots are taken up by this stuff like in the screenshot. Seems that only 1 timeslot is available for voice? Those two also reverted to using 1 frequency as shown in Main & Current, from the January 3rd post from earlier. Malvern & Birchmount seem unaffected.

 

[mciupa]

Your demodulator shows more information than mine does, so I'm unaware of this. I get my best decodes from Finch and Arrow towers.

I'm using SDR#v1.0.0.1732

 

[HiVolt]

I just noticed it this morning. The 3 timeslots being used up for this have greatly reduced the number of decoded transmissions, as even though in the Net Info button the talkgroups do show up, they sometimes do not get decoded even if time slot 4 is empty, or if you have priorities set.

I loaded the old SDR# plugin (the russian one), and all the transmissions come on TS4, even though the first 3 slots appear unpopulated in this client. But if you hit Net Info, you can see others that would normally be there (on Finch Tower). The first slots appear to be taken by the MCCH (which used to be normal) but are now populated with SCCH1 & 2.

In the old Russian plugin, there would never be anything in the top TS1. The newer demodulator just shows it.

 

[Ubbe]

MCCH are the Main Control Channel and SCCH are a Second Control Channel.

You do that to split the load of data transmission from users over several timeslots to avoid congestions. Usually when a lot of GPS positions are transmitted or other frequently sent status messages of the vehicles sensors.

If there are other frequencies to that site, it would have some SCCH to its timeslots but no MCCH as there can only be one main control channel for each site.

TETRA are not simulcast, the sites are on different frequencies, but it transmits the same call over several sites, the ones that the system have registered that a user are listening to the TG. Other sites will not transmit that call. Sometimes you might hear a TG from a site and sometimes you don't if all users on that TG have moved over to another site.

No standard TETRA radio can be used as a listening device as it needs to transmit and register to the system before it can start to listen. The firmware in the radio needs to be modified to "fool" it that it have already done the registration part.

/Ubbe

 

[HiVolt]

Yeah, I understand the way that works. I'm just reporting that the way these control channels seem to take up spots in this demodulator software, it prevents the decoding of talkgroups. I have done a lot of testing today, and a whackload of stuff is not being decoded, because 3/4 time slots in the software are taken up.

Unfortunately, we don't have a luxury of a better easy to use decoder for TETRA.

 

[Ubbe]

There's shouldn't be any problem monitoring using thewraith2008 tetradecoder.

SDR# - TETRA Demodulator Trunk Tracking Demonstration

I've been messing around with SDR# TETRA Demodulator plug-in to see what I could come up with in regards to trunk tracking TETRA. I did this as a stop gap until the big players have come up with something. And in true SDR form, here is the setup. I used 2 instances of SDR# (for CC and VC)...

forums.radioreference.com

My local system has usually 4 frequencies at each site and 2 SCCH's at each frequency and works 100% to monitor.

Some systems has a configuration that only key up as many frequencies that are necessary at each site to handle the load and other configurations key up all there is. Using SCCH's will usually require all frequencies to be keyed up.

TETRA sends out all info in one site about all adjacent sites control channel frequencies. The TETRA radio then samples all the adjacent sites and then keep constant track of the 3 strongest of them. The radio can then switch instantly to the strongest one when their current connection are getting worse without any noticeable glitch in the audio.

The system admin can configure the MCCH and SCCH to use any slot in any frequency at the site.

There seemed to be some misunderstanding of how a TETRA system works, that would make it confusing to try and map out the Toronto system.
All TETRA systems needs to follow the TETRA specification and will need to work in the same way, being it in Toronto or any other part of the world.

The only thing that differs are the configurations like TG's, user ID, number of sites and frequencies. Everything else works in the same way in all TETRA systems to be able to use equipment from different suppliers. Many systems have several different suppliers of radios that different branches of users selects that they think would work the best in their particular work area.

/Ubbe

 

[HiVolt]

Looks like the SRT is being converted to TETRA. I just heard testing on the 100030 talkgroup, talking to SRT car number 3001 and 3002.

Also 100039 for the Passenger PA.

This was on the Malvern tower.

 

[AOD999]

Looks like the SRT is being converted to TETRA. I just heard testing on the 100030 talkgroup, talking to SRT car number 3001 and 3002.

Also 100039 for the Passenger PA.

This was on the Malvern tower.
View attachment 99186

What a waste, set it up for 3 years to get rid of it

 

[HiVolt]

What a waste, set it up for 3 years to get rid of it

It's not that many trains, and they want to consolidate everything onto TETRA comms. The old analog system sounds horrible at times and they can't call individual trains.

Plus, given the TTC and city politics, it could go on for longer...

 

[mapleradio]

After listening last time I was in the area, I am pretty impressed with the TETRA system, very clear and has limited jitter. I am using 2x SDRs on a laptop that is convertible to a tablet in my vehicle with Shark fin Antenna.

 

[HiVolt]

Yeah it is pretty good voice quality. However I still hear a lot of field personnel audio break up and complain about TETRA reception.

Thats sort of the problem with digital systems, once it starts to garble it sounds all robotic or completely nothing... On the old analog systems, even with static you could still make stuff out.

 

[HiVolt]

Well, looks like Birchmount was converted to have these extra control channels... so much less audio coming in now, since this demodulator just can't handle it correctly, even with the trunking addon. Right now the only one that still works well in my end of the city is Malvern, but I suppose it will be converted too because the two other control channels for it are there just not operational yet.



Has anyone figured out how to get anything to make this work? basically no comm coming thru unless it happens to be assigned to Time slot 4.