OP25 Not Decoding Control Channel

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ks13645

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I'm attempting to use OP25 (scope.py) and a NooElec R820T USB SDR to listen to the Sedgwick County, KS, simulcast trunked system. Sedgwick County (Project 25) Emergency Services Radio System Trunking System, Wichita, Kansas - Scanner Frequencies

Everything looks like it should be working right... In "manual" mode, tuned to the control channel, I get a healthy looking differential constellation plot, and the terminal output shows the following:

NAC 0x573 DUID 0xF len 216 errs 0

...but the Traffic tab never populates with the usual system info.

Also, if I try to run in normal mode, with the system NAC and frequency info manually put into the trunk.tsv file, it acts like it's working, but the Traffic tab looks like this:

====== NAC 0x573 ====== Sedgwick ======
rf: syid 0 rfid 0 stid 0 frequency 0.000000 uplink 0.000000
net: syid -1 wacn -1 frequency 0.000000
secondary control channel(s):
stats: tsbks 0 crc 0

In manual mode, if I set the frequency to one of the system voice channels, I can hear whatever traffic happens to land on that channel, so I know I'm getting good data from the system, there's just something odd about the control channel.

Just for background, I have been using OP25 to monitor the Butler County, KS, simulcast trunked system for about a week now, and it works great! When I look at that system's control channel in manual mode, the terminal output looks like this:

NAC 0x1BC DUID 0x7 len 360 errs 0

Any thoughts or suggestions?

Thanks in advance,
--John
 

ks13645

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Problem solved... Defective End User

Problem Solved... OP25 is working fine. This user apparently isn't, though. :)

For whatever reason, there are apparently two "control" channels running on the Sedgwick County system. Only one of them has activity on it. I happened to find the "blank" one as I was configuring OP25, and then found the "real" one later as I was working with a scanner (after I posted my question, of course).

Lesson learned...

--John
 

PiccoIntegra

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In manual mode, if I set the frequency to one of the system voice channels, I can hear whatever traffic happens to land on that channel, so I know I'm getting good data from the system, there's just something odd about the control channel.
Hi John

Looking at the site for that system, RRDB says the modulation is "H-DQPSK 2-slot TDMA". The FCC emission designators (9K80D7W) also reflect this. This may or may not be the problem. I would have guessed this was for voice though, not control channel.

If you have one, what happens when you try an monitor this site with a Phase II scanner?

I'd really like to see a raw IQ dump of this site, but the file size will be in the hundreds of megabytes in size. Do you have a way of getting one to me, and not through email? I can step you through the process if so..

-Scott
 

ks13645

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Hi John

Looking at the site for that system, RRDB says the modulation is "H-DQPSK 2-slot TDMA". The FCC emission designators (9K80D7W) also reflect this. This may or may not be the problem. I would have guessed this was for voice though, not control channel.

If you have one, what happens when you try an monitor this site with a Phase II scanner?

I'd really like to see a raw IQ dump of this site, but the file size will be in the hundreds of megabytes in size. Do you have a way of getting one to me, and not through email? I can step you through the process if so..

-Scott
Hi Scott,

Yes, I can upload large file(s) to Dropbox and send you a link. If I do it right, you shouldn't need an account to download it...

I'll try to post the link here in case anyone else is interested in taking a look.

I remember hearing that the system is licensed for phase 2, but so far, I think all voice traffic is phase 1. Maybe the control channel is phase 2 capable?

Listening to the control channel in FM, it does sound different then the other systems I monitor. Unfortunately, I don't have a phase 2 scanner, but so far, I have been able to monitor it with a phase 1 scanner.

Go ahead with the instructions for capturing the data. I will try to do it Monday at work, when I am closer to the system and can get a better signal.

Thanks,
John
 

PiccoIntegra

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Ha, I didn't see you had solved the problem. I guess I had the original post open in a tab and didn't see the new post.

You can disregard the raw dump if you don't want to fool with it.

What you may have been seeing could have been data transmissions to/from subscribers. The system I monitor does this quite often. OP25 was decoding the data stream though, and the data you posted was from the HDU(NAC and DUID). But it wasn't control channel data, which is why the traffic tab wasn't populated.
 

ks13645

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No problem... I'm still interested in going ahead with the capture if you're still interested in taking a look at it! I'd like to learn how to do the capture anyway. Thanks, -- John
 
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