SDR# TETRA Demodulator Trunk Tracking Demonstration

[Ubbe]

There is no possibility of hearing 12104? Never?

Never.

/Ubbe

 

[ET-NL]

Never is a big word, find the site where 11001 is connected to and you will hear the voice of 12104 (but then you won't hear 11001 anymore).

ET

 

[NikoMAU]

Never is a big word, find the site where 11001 is connected to and you will hear the voice of 12104 (but then you won't hear 11001 anymore).

ET

Hello
Thank you for your reply.
I'm going to look for it lol
I have confirmation that my settings are working well because yesterday I listened to a conversation between 12104 and 12105 (the numbers may not be right, I don't remember) which was in duplex and I heard both speakers, so everything is working
Thanks for your advice and answers
Sincerely
Niko

 

[Ubbe]

Never is a big word, find the site where 11001 is connected to and you will hear the voice of 12104 (but then you won't hear 11001 anymore).

ET

11001 are connected to the same site where 12104 are, but as it is a private call including a dispatcher the 12104 are not heard as the system do not allow the mobile audio to be routed to be repeated out on the site, as no one are needed to listen to it, except the dispatcher listening directly to the RX line from the site.

/Ubbe

 

[ET-NL]

11001 are connected to the same site where 12104 are, but as it is a private call including a dispatcher the 12104 are not heard as the system do not allow the mobile audio to be routed to be repeated out on the site, as no one are needed to listen to it, except the dispatcher listening directly to the RX line from the site.

/Ubbe

Both parties need to hear the other one so a site needs to TX the voice data of the other. If both devices are connected to the same site the site will TX both voice channels. Both devices need to RX the audio of the other and this is only posible if it is transmitted by the site where the listening device is connected to.

 

[NikoMAU]

11001 are connected to the same site where 12104 are, but as it is a private call including a dispatcher the 12104 are not heard as the system do not allow the mobile audio to be routed to be repeated out on the site, as no one are needed to listen to it, except the dispatcher listening directly to the RX line from the site.

/Ubbe

Thank you for your reply.
But then how can the dispatcher hear 12104?
Is 12104 transmitting on a frequency?
I'm sorry if my questions are a bit silly, but I'm new to this and I like to learn, but I'm having a bit of trouble understanding lol
Sincerely

 

[Ubbe]

The site has one receiver on frequency X and one transmitter on another frequency Y. Dispatcher are listening by wire to receiver X and mobile 12104 are listening thru air RF to the transmitter Y, and you can also listen to transmitter Y using your receiver. You will then hear the dispatcher.

Mobile are transmitting using frequency X but you cannot hear frequency X and you cannot decode a mobile transmitter, unless it is transmitting in simplex to another mobile and not using the tetra system, and you must also use the experimental DMO mode in TTT. But you must then be very close to the mobile, maybe less than 1km to be able to hear it.

/Ubbe

 

[ET-NL]

That's true when dispatch is directly wired to the network, but what I see over here is that dispatch is just using normale mobile radio's to communicate. So alle communication goes over the air interface just like any other mobile station.

 

[Ubbe]

That's true when dispatch is directly wired to the network, but what I see over here is that dispatch is just using normale mobile radio's to communicate. So alle communication goes over the air interface just like any other mobile station.

Yes, then it's the same as a mobile to mobile call and it's just a matter of finding which site the dispatcher are using and set the second SDR receiver to listen to that site and the other mobile will be heard on that site.

/Ubbe

 

[NikoMAU]

Hello to you @Ubbe @ET-NL
Thank you for your answers.
Sorry, I use a translator for our conversations, there may be some translation errors sometimes.
As you can see on the picture of my two SDR on the band (42x xxx xxx) I have 6 frequencies in Tetra:
A: same as B but not as loud
B: Where I listen to the duplex
C: Encrypted
D : Encrypted
E : Nothing
F: if I put my CC SDR on this frequency it is automatically switched to B
When you say that I have to put the second SDR on another frequency to listen to the other mobile, is it the SDR CC or the SDR VC that I have to set?
Sincerely

Translated with DeepL

 

[ET-NL]

Hi Niko,

In the tab neighboring cell you should see the information about other sites of this network (if any). Then you have to tune your CC and VC to the other site. If there are no other sites within this network (single site network) than it's likely that dispatchers are directly connected (wired) to the network (like Ubbe suggested earlier) and the audio is not transmitted.

 

[NikoMAU]

Hi Niko,

In the tab neighboring cell you should see the information about other sites of this network (if any). Then you have to tune your CC and VC to the other site. If there are no other sites within this network (single site network) than it's likely that dispatchers are directly connected (wired) to the network (like Ubbe suggested earlier) and the audio is not transmitted.

You mean the "Neighbour cell" tab?
Like in the picture?
If so, what information can I retrieve?
Sincerely
Niko

 

[Ubbe]

You have been listening to LA2 which is site 2 and the neighboring site of LA1 have the channel 1135 which is 428.3875
Set the second SDR to that frequency and check if you can receive it and then if you can see the same call in that site and you should then hear the other party, if it is a mobile radio being used. if you can receive LA1 at 100% quality but there's no call there from the same user ID's as in LA2 then it is a wired dispatcher call and you will never be able to hear the mobile.

When you listen at F and it goes to B it means that both are the same site but B has the control channel and 3 voice slots and F have 4 voice slots.

A are probably site LA1 and it could have one additional frequency E. When you receive A it should say channel 1135 and have a neighboring site LA2. The spectrum looks as if you could increase the gain more in SDR# settings and perhaps improve the reception of E.

/Ubbe

 

[NikoMAU]

You have been listening to LA2 which is site 2 and the neighboring site of LA1 have the channel 1135 which is 428.3875
Set the second SDR to that frequency and check if you can receive it and then if you can see the same call in that site and you should then hear the other party, if it is a mobile radio being used. if you can receive LA1 at 100% quality but there's no call there from the same user ID's as in LA2 then it is a wired dispatcher call and you will never be able to hear the mobile.

When you listen at F and it goes to B it means that both are the same site but B has the control channel and 3 voice slots and F have 4 voice slots.

A are probably site LA1 and it could have one additional frequency E. When you receive A it should say channel 1135 and have a neighboring site LA2. The spectrum looks as if you could increase the gain more in SDR# settings and perhaps improve the reception of E.

/Ubbe

Hello
Thank you for all this information.
I will test this and let you know if it works.
Thanks for your time
Sincerely
Niko

 

[NikoMAU]

Hello @ET-NL and @Ubbe

Thank you for your answers.

If you are talking about the value I circled in red on the image, I can find another site with this value.
Is this the right way to set it up?




If so, I don't understand (sorry I'm a beginner, and I use a translator to communicate with you).
The one I hear is the public transport offices, the one I don't hear is the buses.
As they are buses, they communicate by mobile radio, so I can't understand why I can't receive their signal.

I've tried in every direction but nothing
Maybe I'm just too far away to hear the ones I can't hear, because they're buses with mobile phones?

Anyway, I'm still looking, I'm stubborn lol
Have a nice weekend
Sincerely
Niko

Translated with DeepL

 

[thewraith2008]

Here is the most likely scenario:

Here:
The dispatcher is connected to BS via a land line gateway. (does not use the OTA (Over The Air) uplink or downlink)
The dispatcher voice is sent from the BS gateway to the BS OTA downlink where the MS (and you) here them.
The MS transmits to the uplink and the voice is sent to the dispatcher via the BS land line gateway.
There is no usage of the OTA downlink for MS voice (as it is not needed in this case since the dispatcher does not receive via OTA downlink).

You will not ever hear the MS voice in this scenario.



Latest version (v1.8.6.0) can be found here: MEGA - Download
Release post here

 

[Ubbe]

You don't have to use the Enable AFC function. Calibrate your SDR stick by adjusting the Frequency Correction ppm until your signal looks symetrical inside the blue window. Tetra basestations uses GPS calibration so once you have adjusted the ppm it will be correct for all other use and if you remember the ppm value you can use that in other programs.



I don't know if the Tetra plugin can decode the mobile transmissions. If you tune to 418.3875 in SDR# without starting TTT, do you see any signalling there from the mobiles? They are probably so low powered that you cannot receive them.

/Ubbe

 

[NikoMAU]

Good evening to all
Thank you for your explanations.

It's already a bit clearer in my little brain

MS = Mobile Station, right?
BS = Base Station?

Where I still have trouble understanding if MS is a mobile station, which is the case since they are buses that drive, you say (well the translator), "voice is sent to the dispatcher via the landline gateway" with the translator it means that MS is connected by a cable to the BS. I guess it's not that at all, that would be way too much cable behind the buses lol

Or as @Ubbe suggests the MS signals are too weak for me to hear.

Thanks to both of you for spending time to explain how it all works. If you get tired of doing it, feel free to tell me I'll totally understand :/

Have a nice evening
Niko

Translated with DeepL

 

[NikoMAU]

You don't have to use the Enable AFC function. Calibrate your SDR stick by adjusting the Frequency Correction ppm until your signal looks symetrical inside the blue window. Tetra basestations uses GPS calibration so once you have adjusted the ppm it will be correct for all other use and if you remember the ppm value you can use that in other programs.

Good evening

Thank you for your information on the settings that I have just changed on my side.

I don't know if the Tetra plugin can decode the mobile transmissions. If you tune to 418.3875 in SDR# without starting TTT, do you see any signalling there from the mobiles? They are probably so low powered that you cannot receive them.

/Ubbe

I have tested but all I hear is the noise of the Tetra.
So you are probably right, if I could hear them they are probably too weak for me

Thanks again for your time
Have a nice evening
Niko

 

[Erik211]

"voice is sent to the dispatcher via the landline gateway" with the translator it means that MS is connected by a cable to the BS. I guess it's not that at all, that would be way too much cable behind the buses lol

Maybe your translator messed that up. If you look at thewraith2008's sketch, you see that the land line is between the dispatcher and the base station. In real life the land line can be over internet, private fibre cable or even microwave radio link. (In the old analogue days it used to be a copper cable or sometime a telephone line).

The point is that for that call there is no point of retransmitting the audio of the bus over the base station, because the dispatcher is listening to the basestation's receiver via the land line.

But if two buses talk to each other all transmissions would of course be transmitted from the base station. (At least if they are in a group call. If it's a direct call it could be that they are in different areas and thus one base station transmits the audio from one bus and vice versa).

As Ubbe points out - your only option to hear the buses is to listen to the "uplink" frequency. I'm not sure if that's possible in TTT or with Tetra demodulator. It's for sure not DMO, but I'm not sure it would be the same as decoding TMO either?