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Voice/Control Channel Decoding Software - For discussion of software applications which decode digital voice formats and trunking control channels. Please use the HF Digital Signals forum for anything below 30MHz.

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Old 02-09-2018, 5:30 PM
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Question MPT-1327 decoding

Hey gang,
So I have been browsing around and I found some control and voice channels all in the MPT-1327 mode.
I've tried to decode the control channel with Trunk View and no luck. Then, I told Trunk View to use 'stereo mix' and I went to the Sig ID wiki page and listened to an audio sample and Trunk View started to decode that sample. Yes, I can confirm that I did hear this mode.
Any idea why I am unable to decode the signals that my SDR is picking up? Maybe the coding of the signal is different and the decoder doesn't understand it?
I don't know if the MPT-1327 out in Europe is different than the MPT-1327 over here in Canada or in the USA.
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Old 02-09-2018, 5:51 PM
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SDRTrunk will decode MPT-1327.
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Old 02-09-2018, 6:18 PM
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What service/frequencies are you trying to monitor?
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Old 02-10-2018, 6:11 AM
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Trunkview is a good software to decode MPT1327 . As you find the trunked frequencies , you can drive another Scanner to follow voices .

I was using some years ago a BCT386T with RS332C cable . One scanner on MPT1327 signal and the BCD386T to follow voice

Most of our MPT1327 have migrated to digital (TETRA)

The most active MPT1327 here is French plane company (Air France)
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Old 02-10-2018, 10:26 AM
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I've heard of SDR Trunk but I have difficulty getting it all set up and the JMBE addon won't compile for me.
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Old 02-10-2018, 10:53 AM
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Quote:
Originally Posted by ATCTech View Post
What service/frequencies are you trying to monitor?
Don't know exactly right now but I believe it's around 423 MHz.
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Old 02-10-2018, 11:20 AM
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Quote:
Originally Posted by robman50 View Post
I've heard of SDR Trunk but I have difficulty getting it all set up and the JMBE addon won't compile for me.
You shouldn't need the JMBE library for MPT1327 ... JMBE is only required for P25 audio.

1)Make sure you have a compatible tuner installed and that it works in other SDR programs.
2)Start the sdrtrunk application
3)Create a new channel.
4)Set the 'Source' to tuner and enter the frequency of the control channel.
5)Set the 'Decoder' to MPT-1327
6)Save the channel configuration and click 'Enable'.

If you want to follow traffic channels, you'll need to create a Band Plan and add it to the channel configuration in the decoder tab. If you let the decoder run for a while and then copy all of the call events from the Now Playing window with their channel numbers and post them here, I can help you figure out the band plan.

Denny
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Old 02-10-2018, 11:28 AM
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Here is one of the control channels.
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Old 02-10-2018, 11:44 AM
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Wait a minute here...
TAFL has it listed as 'TORONTO TRANSIT COMMISSION', that's Tetra!
https://www.radioreference.com/apps/db/?sid=9380
Can Tetra be easily mixed up with MPT-1327?
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Old 02-10-2018, 12:15 PM
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It's not their TETRA system Rob, try 422.6625 or 422.6875 to hear it. FYI, it's 25kHz (wide) FM. I also think you'll find the 423.xxxx frequencies you're trying to receive are slightly above the old TTC MPT-1327 frequencies as shown here:

https://www.radioreference.com/apps/db/?sid=2852

although the TAFL does show frequencies above these that don't seem to appear on RR including the analog voice CIS frequencies which seem to be in between the MPT-1327 assignments.

I see 423.2375 as the lowest frequency in that group of alway-on channels up to 423.6500 that I can hear from my QTH. They don't decode anything with Trunkview or SDRTrunk here either, so far!

Bob
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Last edited by ATCTech; 02-10-2018 at 12:30 PM..
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Old 02-10-2018, 1:12 PM
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That's so weird. My SDRplay RSP2 can get the MPT-1327 channels but my RTL-SDR v3's can't.
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Old 02-10-2018, 1:17 PM
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"Can get" as in you can decode the data stream or the RTL doesn't even receive them? I'm using both RTL dongles and an Airspy and they're fine with both as far as tuning/signal quality/strength, just no decoding. Using SDR# here BTW.
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Old 02-10-2018, 1:43 PM
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It could be the RSP2 can pull it in better because of the LNA. I find it brings in more weaker signals that the RTL can't.
It is also likely that the signal is weak to begin with and the loss of the T adapter is to great.
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