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Help finding band plan, MilCom UHF P25

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drsouth

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Hi all,

I'm tring to setup listening to Charleston AFB's new APCO25 digital system, and I'm stuck.

I've tried letting my BCD396t and BCD996t auto find the band plan, but they won't lock onto any talk groups, and just stay on the CC.

Here's what I've been able to find, I can find encrypted and unencrypted digital voice on these freq's:
406.1625
406.3625
406.5625
406.7625
407.1625
407.3625
407.5625
407.7625
the CC is 407.9625

I've tried letting the scanner setup the input base automatically, but it tries to set it to:
851.00625Mhz/6.26khz

I've tried just about every combination I can think of for a band plan, but I just am not getting it. I've also tried using Trunker and and Unitrunker, but they don't like the system either. Infact, they don't follow or see it at all.

Thanks in advance for the help.

David
 

SCPD

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drsouth said:
I've tried just about every combination I can think of for a band plan, but I just am not getting it. I've also tried using Trunker and Unitrunker, but they don't like the system either. Infact, they don't follow or see it at all.
Hi David;

Have you been able to validate your setup? Were you able to get Unitrunker working on any trunking signals in your area?

Try this:

Run Uniscope. Select the appropriate sound input. If you've got a newer version of the Uniscope program - set the symbol type to "oscilloscope". Click "Run" and watch the display. Adjust your signal level so that the signal isn't too flat (like a dead patient on a heart monitor) or to high / clipped. If you've got an older version - find a separate oscilloscope program to do this. Once you know you've got a decent signal level do the following.

If you think this is a 3600 baud Motorola control channel, set the symbol type to "Pulse" and the symbol rate to 3600. Set your sample rate to 44100.

If you think the signal is an actual P25 trunking control channel - set the symbol type to CQPSK and set the symbol rate to 4800 (not 9600 - a common mistake).

If you think your system can handle 48000 or 96000 samples per second - try them.

Click "Run" to watch the eye-pattern display. If you've got a noisy or jittery signal, turn on the "Glass" option. That can make viewing the pattern easier despite any noise.

For a pulse signal, you should see an eye pattern roughly centered in the graph. It may wobble up and down or side-to-side but as long as the center is clear - you've got a decent signal.

For a CQPSK signal - you're looking at all four symbols - each in a different quadrant. The two left-hand squares should be shallow peaks that form mirror images of each other. Same for the right-hand squares - only the peaks should be much taller - but not clipped.

The Air Force system is probably C4FM unless it's simulcast. In that case you're looking for a eye pattern again.

Once you've got good signal then you can move on to actually trying to decode it.

-rick
 

drsouth

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Hi Rick, Thanks for your reply.
I've followed you around for awhile here and in the trunker forums. First let me say thanks for all your hard work on Unitrunker, I have indeed been using it. I've been a trunker man for several years now, have 3-4 local systems I like to leave it on and have accumulated a very large database on then. I've run Unitrunker several times with out results. (Note: I've been using my own flip gate "slicer" serial setup off my old RS pro-43) Not until I ran an audio line-level signal from the same tap as the slicer did I get good useage out of the Unitrunker. But, I know that's a Different topic. Sorry.. but yes, I can run Trunker via slicer output and Unitrunker via Audio tap from the Discriminator point on moto systems without a problem. Several of the moto systems here have Astro capable talk groups, so I've seen them run fairly well on digital signals. This completely digital signal is nothing like what I've seen before.

I work on the Base, and have taken my 396 & 996 with me, it defiantly sees the Control channel strong, if I set my BCD996t or the 396 to anything other than P25 the CC has the extremely fast buzz sound (sort of like a normal moto control channel sound, but much faster with more pronounced pauses and clicks). Both scanners seem happy looking at the system as a P25. They lock onto the CC and show searching, yet they never stop on any talk group. To pause either radio on the CC, you can see the radio group ID's alternating, and like I said in my earlier post, I have "stumbled" onto the voice channels and heard non-encrypted traffic on them by doing a freq search.

I've applied what I know of calculating bandplans and from the wiki section and I still can't come up with a band plan that works. While either scanner is scanning or searching, it will not even pause unless the 3rd (0,1,2) band plan has something in it. I've tried 382, and other derivatives of that. Using .0125 offsets etc.. Have spent several weeks on this and am very frustrated. In other words, I have more luck scanning the trunked channels like the days before trunked scanners, than having any luck following this one particular system.

I'm sorry for the rant, just frustrated with this tuff nut to crack, I still love the fun in this hobby, and just sometimes I can't see the forest for the trees ya know? Thanks for the help,

David
 
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drsouth

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Sorry, that wasn't a very good representation, had the drive line up too high.. these are two screen shots of the signal as a C4FM and CQPSK

David

{edit} forgot to mention, the CQPSK signal "rolls" in that the waves are scrolling left to right in a exaggerated accelleration. First slowly, then almost pausing to a stop, then fast and then it inverts. I hope that sounds clear, I know I'm confused!
 
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drsouth

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Rick, I think I need to specify, Unitrunker tries to decode the system, in that about every 30 secs, it flashes:
LCN 00-0000
Frequency 851.00625

and has under the Pr[o]ps tab:
NAC fff
Callsign
Modulation CQPSK
Profile 2.25 (have seen 2.61, 2.12, 2.64, 2.73, 2.92... keeps changing)

but, most of the time it's just "no signal"


Again, thank you for your time and patience, I'm sure this is something I'm just not getting.


any chance this might be one of the encrypted CC's I seen you talk about? I wouldn't know what one looks like to know for sure.

David
 

drsouth

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I have managed to get a Packet dump with Unitrunker. I'm afraid that posting such a large entry would upset the group. So, I've saved it as a text and attached it here. I hope this sheds some light on things.

David
 
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drsouth

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The only interesting thing I can find in the packet dump, are these comments, and they change every so many seconds. Here's a snippet from the attached text:

E-B4 00 01 40 21 30 13 80 00 00 78 22 463D Identifier Update 0 Base 1635778560 Spacing 6000 Tx Offset 1026000000
E 34 00 01 04 01 02 01 00 00 00 28 0A 0ED3 Identifier Update 0 Base 83886080 Spacing 250 Tx Offset 64000000
E-B4 00 01 00 00 13 C3 22 00 00 74 E9 76E0 Identifier Update 0 Base -810942464 Spacing 2375 Tx Offset 0
E 34 00 01 01 45 01 C7 00 04 90 18 73 2E57 Identifier Update 0 Base -486533424 Spacing 125 Tx Offset 20250000


Are APCO 25 CC's capable of randomizing their base/offset and Tx/Rx spacing? and if so, are we able to listen with our digital scanners? Is this why my scanners can't follow this system?

Ok, I'm done on this for awhile.. Letting the people in the know have a go.

David
 

mikey60

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This looks to me to be a MA/COM P25 implementation. For some reason MA/COM likes to set up the system in a similar fashon to an EDACS system, where LCNs are used instead of the more standard Table-Channel configuration Motorola uses.

While the Decode you provided has a number of errors in it (pretty much every line is showing a decode error), it does show typical packets for this style of configuration. I don't think you're going to get a Uniden radio to track this system. The Pro-96/2096 can be made to do it, but would require two banks since there are more than 6 frequencies in the system.

These lines suggest the MA/COM Configuration:

Group Voice Grant channel 2-000(851.00625)
Group Voice Grant channel 3-000(851.00625)

Note the Table number (2 and 3) followed by the channel number of 000. Treat the system as an EDACS system and try to find which frequencies match the LCN (in this case the table number) and go from there. If you have a Pro-96, you can enter in tables that will track it, Probably not on the Unidens unless there is access to modify the table configurations on the 396 or 996.

Mike
 

drsouth

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Hi Mike, and thanks for your reply!

I guess I won't be listening to the base any longer since the two uniden's are the only digital radio's I have. I appreciate your looking into this for me. 'been a definate challenge to figure this one out.

David
 

SCPD

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As Mike points out, the "E" in first column means the packet had errors that could not be corrected. It looks like a few of the continuation messages were close enough to see what was going on as far as channel assignments. Personally I think an MA/COM engineer was smoking crack when they chose that channel scheme. It limits you to 16 channels - and wastes up to 24 bits per message. What they should have done was designate a particular identifier as the "EDACS style" LCN prefix. That way they could still interoperate with non MA/COM sites (eg. support neighbor site broadcasts). One can only hope.

The eye pattern on the C4FM signal (it is definitely C4FM) looks decent enough. The three eyes are evident though there is some skew / jitter. You might want to consider installing a small buffer amplifier. That might be enough to push you just over the edge into solid decoding. Eventually I'll get radios like the 396 and 996 support for voice following. You'd have to manually enter the frequencies - just like EDACS (or perhaps download them from the DB).

-rick
 

drsouth

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thanks fo all the help!

Thanks Rick and Mike, makes since to me now. Just frustrates me that my setup at the house can pickup VHF/UHF/800 trunk sites from a long ways out, and even with propagation on sites over 150miles away, I have better error rates than I do on this system.

Just to ease my mind, I drove over to the "SP" shack on base, and watched to see the error rate on the 'ol laptop, not much changed.. still have less than 2% rate. seems odd. Same setup (tapped scanner, audio and slicer w/ com port running on laptop) got 94% error rates from Shaw AFB which is over an hour and a half's drive away (they are a "normal" VHF Apco25 system) Guess they have some bugs to work out on the system here.

As far as the DB, I'll see what I can come up with to help the South Carolina lists out. They don't have the old UHF freq's that just got updated to this system.. and from the looks of things, won't be easy to follow anyway.

Thanks again for the help and efforts in putting all this together guys, my hats off to ya’ll!

David
 

drsouth

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tonights view, little better resolution

Here's some screen shots of the system in question from tonight. Approx 80yrds away from the tower.

the scope picks where taken during the packet dump. Sorry about the Error rate, seems to be the best my pro old RS pr-43 can do.

──────┤ APCO P25 System 00001-001 unnamed Site 001-001 unnamed Qual 71%├───────
LCN▌ Frequency▌Pr▌Destination Party ▌ ID▌T▌ID ▌Calling Party▌ CT
00-0000 851.00625
01-0000 0.00000
02-0000 0.00000 50 4 G 49 4
03-0000 0.00000
04-0000 0.00000
05-0000 0.00000
06-0000 0.00000
07-0000 0.00000
08-0000 0.00000
09-0000 0.00000
─────────────────────────────────┤ Properties ├─────────────────────────────────
Key▌Value
NAC 001
CallSign
Modulatio CQPSK
Profile 1.49
 
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drsouth

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Case Closed, system is trunked!!

First, let me say thanks so much guys, finally figured it out!

Thanks go to Rick and his Unitrunker program, and Mike with his EDACS knowledge!

I sat and watched as the radios affiliated, and was able to deduce which units were flight line (non-encrypted) MOS squadrons. As they keyed up, Unitrunker would align them on channel 0X-0000 (Rick, for what it's worth... I had Unitrunker setup with a Sample Rate of 44100. I've never gotten that speed to work on any moto systems, but it sure likes this one!

So, I just programmed in all the Freq's I had heard them keying on, like you suggested with an EDACS system.. Well, I was able to finnaly figure out where to align channel's with Freq's and editing the Band plan in both the unidens to the corresponding channels and spacing, works like a champ!

Again, thanks to all!

Now I can finally go to bed! You guys are the greatest!
 

DaveIN

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Interesting! A 400MHz, EDACS P25 mil-system. How well are your radios tracking? How does the audio sound?
 

drsouth

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Hi Dave!, sounds great (when they arn't encrypted!)
I took Mike's Idea, and just edited the uniden's bandplan (0-8) in order of the LCN's. What's really interesting, is all of the "base" radios are always enrypted, most of the mobiles are not.. so I've been able to figure out what talk groups are what today in pretty fast order.

here's what it looks like on paper:

APCO 25 System
control channel: 407.9625

LCN (MHz) Spacing (Hz)
Band0 407.762500 6.250
Band1 407.562500 6.250
Band2 407.362500 6.250
Band3 407.162500 6.250
Band4 406.962500 6.250
Band5 406.762500 6.250
Band6 406.562500 6.250
Band7 406.362500 6.250
Band8 406.162500 6.250
TG Ids:
1: Base Fire Rescue (AR crash/recovery)
2: Ravens (Security Forces)
3: LE (Security Forces, Law Enforcement)
4: ?
5: ?
6: ?
10: ?Think this is the Super's Group
12: Defender (ECP)
26: Blue (MOS Specialists Flight)
37: Gold (MOS Crew Chiefs)
45: Viper (MOS AGE)


Audio is clean and clear, Have the BCD996t decode rate set on 6-auto, and the BCD396t set on 7-auto. Both following in step very nicely!

I tell ya, this was a weird nut to crack, thanks for the help!
 
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fmon

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DaveIN said:
Interesting! A 400MHz, EDACS P25 mil-system. How well are your radios tracking? How does the audio sound?
A few on this page. http://www.macom-wireless.com/hydra/roster.asp Click on the Flight Deck Coms button to review some of the details. A few of these ships homeport less then 6 miles (mostly across water) from where I'm sitting. However, signals are not very strong.
 

drsouth

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fmon said:
A few on this page. http://www.macom-wireless.com/hydra/roster.asp Click on the Flight Deck Coms button to review some of the details. A few of these ships homeport less then 6 miles (mostly across water) from where I'm sitting. However, signals are not very strong.

Hey, thanks for the interesting read! I'll be on the listen for some of those systems when I'm out and about near the harbor next time!

I'm just pleased that this system is intergrating as well as it has. For years they've been using conventional 400Mhz radio out here but they've never been trunked untill now. On a good clear night, I can recieve Shaw AFB's P25 system.. their's is straight forward though, no tables to mess with.

I've heard some talk that MCAS Beaufort is also in the process of changing over to a new system. Guess we'll need to keep an ear out!

David
 

rescue161

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I've monitored 380-420 EDACS systems with the 396 without problem in the past.

Funny thing is on most of those Hydra systems, the frequencies are pretty much the same for every ship. When two or more ships are in port, you can hear them at all due to their CC's walking all over each other. Same goes for Motorola systems on Navy ships.
 

rescue161

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Yes, I was. I still have them programmed into my 396 and still have the UniTrunker files for them.

They never stayed in port long enough for me to get a complete lists of talk groups, so the data has a lot of holes, but the frequencies and LCN's are correct.

I never submitted them 'cause it just didn't feel right. I mean these are my brothers and they are going to foriegn ports with an unencrypted TRS. I couldn't believe some of the info that they passed over those systems.

It's a little different for a land based system that doesn't move into a potential war zone like a ship can.
 
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