DSD+ p25 Decoding Problems

miked0130

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Sep 29, 2017
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Hi everyone, first time poster but long time browser. I'm hoping I can get some help with some p25 phase 1 decoding using SDR# and DSD+. I have been messing with this for a while now and just can't seem to get it right. I am trying to listen to the public service trunked systemic the city I am in but it is 95% unreadable, mostly all choppy jumbled noises. Coincidentally, the town next to me I can hear crystal clear. Granted the one I am having difficulties with is in the 800MHz band while the adjacent city uses 2m. However I am using an 800MHz antenna (a few of them actually).

Here is my setup, let me know if you need any more info, I would be happy to provide.

- RTL-SDR into a boot camp windows 10 computer
- SDR# scans the voice channels not the control
- Virtual cable routes the data to DSD+ which decodes and throws up tons of error messages
- I ran DSDtune without much improvement, if any at all

Interestingly, there seems to be one talk group I can understand slightly (sounds like DPW), the rest are complete gibberish. I am getting a strong signal with little static when listening to the un-decoded audio. I also drove within about ¾ of a mile of one of the repeaters and pointed an 800MHz yagi at it without improvement. This really makes me think it is not a reception issue but likely something I'm doing.

The CPU is only running at 50% max and that is mainly from the scanning.

Gain control is off, sample rate is 1.92 (tried them all), RF gain is about 44dB, bandwidth is 10,000 (this seemed to work better than 12.5), order is 500 (no idea what this does), and volume is set to about 80% max on virtual cable (it is not clipping the audio). The filter is set to Blackman-Harris 4. I tried but I cant turn this off.

Is there anything I am missing that someone can think of? I appreciate any feedback!
 

slicerwizard

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Sounds like you're monitoring a site that uses PSK modulation. If you're using DSD+ 1.101, add the -mp PSK switch to the DSD+ command line.

If you're using DSD+ Fast Lane, lose SDR#. Hell, I'd lose SDR# with DSD+ 1.101 as well...

What does the audio signal look like in DSD+? Post a screen shot.
 

moonbounce

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I don"t see where it was established that it is a PSK issue, but if it was he could still use DSD+ 1.101 and Unitrunker and the -mp switch.
 

miked0130

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Sep 29, 2017
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Thank you all for the feedback, this gives me a few more things to try! I will post a screenshot later when I get to the computer.

I will try running FMP24 later as well.

I thought with unitrunker I had to use two dongles. I don't have two at this point but could always get another.

Should I upgrade to DSD+ fastlane?
 

moonbounce

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Thank you all for the feedback, this gives me a few more things to try! I will post a screenshot later when I get to the computer.

I will try running FMP24 later as well.

I thought with unitrunker I had to use two dongles. I don't have two at this point but could always get another.

Should I upgrade to DSD+ fastlane?
Using Unitrunker and DSD+ 1.101 you can use one dongle, that is what I have.
 

miked0130

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Sep 29, 2017
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Here are some screenshots of the setup. The first is prior to the -mp command and the second is after. WOW! I think that did it. Such an easy thing I must have missed at some point. You can see the error messages are significantly shorter and the audio is pretty much fully comprehendible.

I still plan on trying unitrunker and FMP to play around with them. SDR# eats through the battery life on the laptop. Now that it is decoding the talk groups are appearing so I will have to add some aliases.

Thanks everyone! I will keep updating this if anything changes.

By the way, how would I know if a system uses PSK? Do I just try the command or is it listed somewhere?

8705987060
 

a417

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SDR# is frequently more trouble than it's worth with DSD+. There are people who "NEED TO SEE THE FREQUENCIES" and use virtual cables and all that nonsense, and then there's the FMP24 crowd.
 

slicerwizard

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I don"t see where it was established that it is a PSK issue, but if it was he could still use DSD+ 1.101 and Unitrunker and the -mp switch.
It's 110% a PSK issue. Those DSD+ audio displays are showing FM demodulated PSK. No other digital modulation - C4FM, etc. - looks like that after being run through an FM demodulator.
 

miked0130

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It's 110% a PSK issue. Those DSD+ audio displays are showing FM demodulated PSK. No other digital modulation - C4FM, etc. - looks like that after being run through an FM demodulator.

I am curious what you are seeing in the audio displays that make you say that.

Also, am I correct in thinking that I should be able to tell what type of digital encoding is being used by the appearance of the waveform?
 

mtindor

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I am curious what you are seeing in the audio displays that make you say that.

Also, am I correct in thinking that I should be able to tell what type of digital encoding is being used by the appearance of the waveform?
Good grief. Just get the Fast Lane version and use FMP24 + DSDPlus TCP-linked together. Forget about SDR#. I am betting that the system you are monitoring is in the RRDB, right? If so, it's going to state whether that site is simulcast or not.. Either it will list it aas Simulcast in the name or it will have a "_____ county" as the name, or it might list it in the site details on RR. But just about any simulcast P25 system that has ever been submitted to RR is listed in some way that it will tell you it is simulcast. It might say "simulcast", or "LSM" or "CQPSK" or any number of things.

And, taking an LSM signal and piping it through SDRSharp and a virtual cable is not going to give you the results you are looking for. DSDPlus Fast Lane with FMP24 + DSDPlus TCP-linked together is what you need.

Yes, lots of people are savvy enough to be able to look at a waveform and/or listen to a signal and tell you if it's a P25 LSM signal or not. Rather than asking how you can learn how to determine that yourself just by looking at a waveform, why not take somebody's word for it that it is LSM, that you are doing it wrong, and that you need to do it the right way?

Mike
 

miked0130

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Good grief. Just get the Fast Lane version and use FMP24 + DSDPlus TCP-linked together. Forget about SDR#. I am betting that the system you are monitoring is in the RRDB, right? If so, it's going to state whether that site is simulcast or not.. Either it will list it aas Simulcast in the name or it will have a "_____ county" as the name, or it might list it in the site details on RR. But just about any simulcast P25 system that has ever been submitted to RR is listed in some way that it will tell you it is simulcast. It might say "simulcast", or "LSM" or "CQPSK" or any number of things.

And, taking an LSM signal and piping it through SDRSharp and a virtual cable is not going to give you the results you are looking for. DSDPlus Fast Lane with FMP24 + DSDPlus TCP-linked together is what you need.

Yes, lots of people are savvy enough to be able to look at a waveform and/or listen to a signal and tell you if it's a P25 LSM signal or not. Rather than asking how you can learn how to determine that yourself just by looking at a waveform, why not take somebody's word for it that it is LSM, that you are doing it wrong, and that you need to do it the right way?

Mike
I'm just trying to learn here. I am not saying I don't believe anyone. Wouldn't it be more beneficial for me to try to learn how to do it myself rather than rely on other people? Thought it was a learning opportunity, sorry if I offended anyone.

As I already said, I am planning on playing with FMP24 and potentially fast lane. Right now though, it is working thanks to the other members, and I really appreciate that!
 

batdude

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I'm just trying to learn here. I am not saying I don't believe anyone. Wouldn't it be more beneficial for me to try to learn how to do it myself rather than rely on other people? Thought it was a learning opportunity, sorry if I offended anyone.

As I already said, I am planning on playing with FMP24 and potentially fast lane. Right now though, it is working thanks to the other members, and I really appreciate that!
i'll add that I screwed around with SDR# and VB audio cable crap for a year.... within an hour I had FMPA.exe working 100% better than SDR# ever even thought about running. Get FastLane. it works.


doug
 

slicerwizard

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I am curious what you are seeing in the audio displays that make you say that.
Some modulation schemes aren't difficult to spot.

Also, am I correct in thinking that I should be able to tell what type of digital encoding is being used by the appearance of the waveform?
No, waveforms can show modulation types, not protocol/encoding schemes; not much difference in the appearance of 4 level Fusion or NXDN or DMR...


2 Level D-Star:
2 Level D-Star.png


4 level FSK/C4FM P25:
FSK P25.png


PSK P25:
PSK P25.png
 

miked0130

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miked0130

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Sep 29, 2017
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Well I did it! Purchased fastlane and using that with FMP24 and things run flawlessly. You just open the files and it works, no messing around with anything. I definitely recommend it to anyone considering it. Thank you to everyone that helped!

Another question while I'm on here. Is there the possibility to add a single channel to monitor in addition to the P25 trunked system? Essentially, it would be nice to monitor the local trunked system but also an additional town at the same time.

Appreciate it in advance!
 

miked0130

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I did some reading and see this is possible using the FMP24.scanlist file. However, I do not have this file and cant find it anywhere. Is there anywhere I can go to download it or create it myself?
 

mtindor

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I did some reading and see this is possible using the FMP24.scanlist file. However, I do not have this file and cant find it anywhere. Is there anywhere I can go to download it or create it myself?
Just create it yourself with a text editor (like Notepad if you are on Windows). Make sure it doesn't end in .txt when you save it.

Also, read all of the relevant TXT files -- such as Notes.txt, DSDPlus.txt and any other .txt files. In Notes.txt, search for 'scanlist' to find where it talks about the scanlist files.

Mike
 
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