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  #1 (permalink)  
Old 07-26-2017, 6:02 PM
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Default Has anyone made a program to listen to digital trunked police radio?

Thats one thing I have never seen. I still have to use my radio shack scanner if I want to listen to maryland police or government radio. Its not encrypted so I don't see why it would work. But I have also heard that someone tried to make a an analog trunked system from dongles but they needed two. Couldn't the SDR listen to two frequencies at once? I have an SDRPlay so I know it does alot more then the dongles but yet to see SDR replace a scanner.
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Old 07-26-2017, 6:40 PM
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There are several programs that do trunking-most recommend two receivers. I think DSD Plus is popular. I have not tried any SDR for trunking as I use normal scanners for that. You might browse this and the Voice/Control Channel Decoding software forum for other information.
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Old 07-26-2017, 6:52 PM
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Quote:
Originally Posted by beamin View Post
Thats one thing I have never seen. I still have to use my radio shack scanner if I want to listen to maryland police or government radio. Its not encrypted so I don't see why it would work. But I have also heard that someone tried to make a an analog trunked system from dongles but they needed two. Couldn't the SDR listen to two frequencies at once? I have an SDRPlay so I know it does alot more then the dongles but yet to see SDR replace a scanner.
Most of the inexpensive RTL-SDR dongles have a limited bandwidth and can only receive about 2 MHz at a time. If you only have one of them, it can be difficult for the trunk tracking software to listen to the trunking control channel and various voice channels if they are more than 2 MHz apart in frequency. That is why most people use two of them.
Here is an example using only one RTL-SDR dongle.
Listening to Trunked Radios with One RTL-SDR

Here is a tutorial using two RTL-SDR dongles to follow trunked radio:
RTL-SDR Tutorial: Following Trunked Radio with Unitrunker

Here is more information on decoding digital audio using a RTL-SDR receiver:
RTL-SDR Tutorial: Decoding Digital Voice (P25, DMR, NXDN, D-STAR) with DSD
DSD+ Version 1.5 Released
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Old 07-26-2017, 7:29 PM
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If you run Linux you might want to checkout the trunk-recorder project.
https://github.com/robotastic/trunk-recorder

I use it for recording my trunk system and love it.
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Old 07-26-2017, 10:02 PM
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Quote:
Originally Posted by beamin View Post
Thats one thing I have never seen. I still have to use my radio shack scanner if I want to listen to maryland police or government radio. Its not encrypted so I don't see why it would work. But I have also heard that someone tried to make a an analog trunked system from dongles but they needed two. Couldn't the SDR listen to two frequencies at once? I have an SDRPlay so I know it does alot more then the dongles but yet to see SDR replace a scanner.
First thing to figure out is what type of system you wish to monitor and from there you can determine what software and hardware you'll need. The software for P25 Phase 2 is very different from Motorola Smartzone for example.
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Old 08-04-2017, 1:01 AM
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I use DSD plus with SDRSharp and have no problems decoding P25 and DMR. No bandwidth issues or anything like that. I use one rtl sdr dongle with virtual cable installed on my windows 10 laptop. DSD plus also auto selects between various modes to decode and playback. I really like these cheap sdr dongles. Never heard of then till about 3 months ago.
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Old 08-06-2017, 6:35 AM
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Default guide dsd+ sdr# p25

BamaChad
would you mind posting a guide I could follow to set my dongle up using dsd+ and sdr# for p25. I tried some methods/guides. Finally got it working using unitrunker but would like to learn other methods. thank you

kenny70452@gmail.com

Last edited by Dufus; 08-06-2017 at 6:36 AM.. Reason: add info
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Old 08-06-2017, 9:19 AM
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Quote:
Originally Posted by boatbod View Post
First thing to figure out is what type of system you wish to monitor and from there you can determine what software and hardware you'll need. The software for P25 Phase 2 is very different from Motorola Smartzone for example.
Smartzone is what Motorola calls their multi-site arrangement regardless of whether or not it's Type 2 (SmartNet/Privacy Plus), Astro 25 (Phase 1) or Astro 25 TDMA (Phase 2).

However, OP25 will work with all three systems.
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Old 08-06-2017, 11:55 AM
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Quote:
Originally Posted by MCore25 View Post
Smartzone is what Motorola calls their multi-site arrangement regardless of whether or not it's Type 2 (SmartNet/Privacy Plus), Astro 25 (Phase 1) or Astro 25 TDMA (Phase 2).

However, OP25 will work with all three systems.
OP25 works well for 9600bps P25 control channel / Phase 1 (fdma) and Phase 2 (tdma) voice, but not as far as I know on the old Moto Type II Astro 3600bps system. Unitrunker does, but of course that runs under Windows not Linux.
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Old 08-06-2017, 1:56 PM
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Quote:
Originally Posted by boatbod View Post
OP25 works well for 9600bps P25 control channel / Phase 1 (fdma) and Phase 2 (tdma) voice, but not as far as I know on the old Moto Type II Astro 3600bps system. Unitrunker does, but of course that runs under Windows not Linux.


Now I remember, there are previsions in the software to support Type II but it looks like it isn't (and likely won't be) implemented.


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Old 08-06-2017, 4:58 PM
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Quote:
Originally Posted by MCore25 View Post
Now I remember, there are previsions in the software to support Type II but it looks like it isn't (and likely won't be) implemented.


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Trunk Recorder (which uses a modified form of op25) can handle the older systems, but it's not likely to be something added to native op25 since they are gradually being replaced out in the field.
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Old 11-13-2017, 5:10 PM
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Easy - (2) RTLSDR USB receivers ----> Unitrunker ---> VB or similar audio software cable ---> DSD decoder to your sound card. Need to download the band plan for the trunked system from Radio Reference.

Woops! I think I replied to the wrong post.

Last edited by KF6ORX; 11-13-2017 at 5:15 PM.. Reason: Replied to wrong post.
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Old 11-13-2017, 6:15 PM
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As boatbod mentioned, OP25 won't support type 2 systems as they are not P25 compliant - in that they use 2 level FSK control channel.

These systems do (did?) occasionally have P25-CAI-esque voice channels in them, that OP25 is capable of decoding, but it can't trunk-track the conversations on them unfortunately.


Quote:
Originally Posted by MCore25 View Post
Smartzone is what Motorola calls their multi-site arrangement regardless of whether or not it's Type 2 (SmartNet/Privacy Plus), Astro 25 (Phase 1) or Astro 25 TDMA (Phase 2).

However, OP25 will work with all three systems.
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Old 11-13-2017, 11:42 PM
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Quote:
Originally Posted by beamin View Post
Thats one thing I have never seen. I still have to use my radio shack scanner if I want to listen to maryland police or government radio. Its not encrypted so I don't see why it would work. But I have also heard that someone tried to make a an analog trunked system from dongles but they needed two. Couldn't the SDR listen to two frequencies at once? I have an SDRPlay so I know it does alot more then the dongles but yet to see SDR replace a scanner.
DSD+ FastLane with the included FMP program and two cheap dongles works great for digital trunked systems. One dongle monitors the control channel and the other is auto tuned to the voice channels. Fine for NXDN, P25P1, etc. Does not do P25P2 yet.
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Old 11-14-2017, 9:00 AM
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Quote:
Originally Posted by M105 View Post
DSD+ FastLane with the included FMP program and two cheap dongles works great for digital trunked systems. One dongle monitors the control channel and the other is auto tuned to the voice channels. Fine for NXDN, P25P1, etc. Does not do P25P2 yet.
That's where some setups differ. If just interested in P25 (my former thoughts were corrected) you can trunk track with a single SDR using the linux based OP25. The setup can monitor multiple channels at once via the SDR's available instantaneous bandwidth including the control channel. If a talk group is issued a resource out of the bandwidth though...the program will get off of the control channel and follow the talk group appropriately.
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Old 11-14-2017, 12:04 PM
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You can monitor communications on a trunked system with a single dongle, provided the software knows to retune the dongle to the control channel when the channel grant expires or is terminated.

Doing it that way, you can't prioritize talkgroups or monitor overall activity on the system.
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Old 11-14-2017, 9:24 PM
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Originally Posted by DaveNF2G View Post
You can monitor communications on a trunked system with a single dongle, provided the software knows to retune the dongle to the control channel when the channel grant expires or is terminated.

Doing it that way, you can't prioritize talkgroups or monitor overall activity on the system.
True but the dongles are cheap and it takes time to reacquire the control channel and start decoding it again and time to tune to a voice channel and start decoding it. It just makes sense to use two dongles.

What I do wish for is a piece of software that truly emulates a scanner. It would provide a user interface similar to a desktop scanner and control two dongles doing the work on USB ports. I think a lot of users are turned off by all the .bat files, drivers, text files full of frequency lists etc. It would be great to have it all combined into a familiar scanner like a Uniden or Whistler style with programmable channels, talk groups, etc. I would be willing to pay for a Windows version of that!
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Old 11-15-2017, 10:09 AM
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I think if you want an idea of how much it will cost, you should look at some of the existing commercial SDR lines such as Flex. It is doubtful that someone is going to develop another version of something that sells for hundreds or thousands of dollars and give it away (unless they are pirating the software).
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Old 11-15-2017, 12:30 PM
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Quote:
Originally Posted by M105 View Post
True but the dongles are cheap and it takes time to reacquire the control channel and start decoding it again and time to tune to a voice channel and start decoding it. It just makes sense to use two dongles.

What I do wish for is a piece of software that truly emulates a scanner. It would provide a user interface similar to a desktop scanner and control two dongles doing the work on USB ports. I think a lot of users are turned off by all the .bat files, drivers, text files full of frequency lists etc. It would be great to have it all combined into a familiar scanner like a Uniden or Whistler style with programmable channels, talk groups, etc. I would be willing to pay for a Windows version of that!
You do realize that a "scanner" only has a single radio and therefore tunes at roughly the same speed as an RTL dongle. Moreover, scanners do a far worse job of following P25 systems than SDR based applications such as unitrunker and op25.

Actually I think you'll find in a practical application the speed of retuning is a non-issue. For example, on my single RTL op25 system the unit can tune from control channel to voice channel fast enough to catch the first PTT_PDU before the 4V/2V voice bursts hits the airwaves. The only reason for continuously monitoring a control channel is either to capture multiple systems in parallel, or to add priority scanning/preemption.
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Old 11-15-2017, 5:40 PM
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Originally Posted by boatbod View Post
You do realize that a "scanner" only has a single radio and therefore tunes at roughly the same speed as an RTL dongle.
Tuning isn't the end of the story, you have to capture enough bits to start decoding. Dongles are so cheap, just leave one parked on the CC.
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