Decoding P25 NSWGRN information

Decoding P25 NSWGRN information

Postby Bigfella237 » Fri Sep 03, 2010 4:58 pm

Scotty has asked me (in a PM) about how I decode the control channel info of our new P25 GRN, I hope you don't mind Scotty but I thought it would be easier to open up a discussion that everybody could join in on?

On the old 4.1 network (with a 3600 baud CC) it was a lot easier to decode the control channel data, just about any analog scanner with an easy-to-do mod (called a discriminator tap) was capable of feeding the info to a computer through the soundcard so it could be decoded with software (which I'll get to in a minute). However, with the upgrade to P25 (and more importantly to this discussion, a 9600 baud CC), a computer's sound card just doesn't have the audio quality necessary to pass three times as much data to the software. In other words, you will have very little success with P25 trunk sites unless you have one of the newer scanners with control channel data output (also known as CC Dump)?

I must also mention the FSK interface (or "data slicer") which takes audio from a scanner's discriminator tap and converts it to serial data, which when connected to the computer's COM port is another way of supplying the data to the software; however, others might have had more luck with this but I still couldn't get a slicer to work on a P25 CC? Even with a very strong signal I was getting a very poor decode rate... less than 5% which is pretty much useless!

So, which scanners have CC Dump? As far as I know the following list:

Dick Smith Electronics DTS96
Radioshack PRO96
Radioshack PRO106
Radioshack PRO197
Radioshack PRO2096
GRE PSR500 (and PSR500C)
GRE PSR600 (and PSR600C)
Uniden BCD396XT
Uniden BCD996XT
(and according to the PRO96COM website) Anritsu S412D Monitor (whatever that is?)

There are a couple of others with the CC Dump feature (the Uniden BCT15X for example) which are analog only scanners so I haven't bothered to mention them here.

It is worth noting that some of the above scanners will also display the radio ID (known in some of the brands as UID or Unit ID) as well as the talkgroup ID on the scanner itself without the use of any software, and I know the Unidens at least will allow you to alpha tag RIDs in much the same way as TGIDs, so a unit's callsign (or name) will appear on the screen in place of it's number.

Now to the software... there are a couple of popular choices for decoding software, there's a program called "PRO96COM" (available from this website) and then there's one called "UniTrunker" (available from this website). PRO96COM is probably the more "user friendly" of the two but I prefer UniTrunker myself, mainly for it's ability to decode and display multiple sites simultaneously and all using the same database (i.e. tag a RID on one screen and it's instantly tagged across all sites being monitored on the same system).

Both essentially do the same job so have a look at them and decide for yourself? BTW, both of the above software packages are FREE (who says nothing good is ever free these days)! There are some other programs around, such as "ID Trunker III", but the two above I would say are the most popular.

I think that about covers it, if I've overlooked anything I'm sure somebody else will chime in... Have fun!

Andrew

EDIT: Correcting a scanner model, thanks to Sigint for spotting it
Last edited by Bigfella237 on Fri Sep 03, 2010 11:08 pm, edited 2 times in total.
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Re: Decoding P25 NSWGRN information

Postby Bigfella237 » Fri Sep 03, 2010 6:13 pm

Also, Sigint just pointed out that I should mention that "it is ONLY the XT version of the [Uniden] 396 and 996 that has the CC Dump feature, and not the more common T version." Also, only the older "T" version was released by Uniden Australia before they abandoned the Aussie scanner enthusiast, if you want an "XT" model you will have to import it from the US yourself.

Oh yeah, the Anritsu S412D is apparently a high-end piece of test equipment...

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Re: Decoding P25 NSWGRN information

Postby citabria » Fri Sep 03, 2010 6:46 pm

Bigfella237 wrote:However, with the upgrade to P25 (and more importantly to this discussion, a 9600 baud CC), a computer's sound card just doesn't have the audio quality necessary to pass three times as much data to the software. In other words, you will have very little success with P25 trunk sites unless you have one of the newer scanners with control channel data output..


I disagree with this point in principle. I have done large amounts of work using sound cards to both receive and transmit P25 signals, and I can state that a sound card has over 10 times the required bandwidth and more than enough resolution to accurately pass a P25 signal. In fact, one P25 equipment manufacturer in the USA uses an PC and sound card with an analog Kenwood radio to transmit P25 packets.

A P25 signal is 4800 baud (not 9600) and nearly all sound cards go to 96,000 samples per second. That gives us 10x oversampling, which is more than you ever need in practice.

The reason why 2 level FSK is easier to decode is that it works even if your radio and discriminator tap setup is completely shit. 4FSK requires accurate level matching which no one ever bothers to do. This is root cause of the problem - its nothing to do with the soundcard itself. Yes, P25 signals do require more effort to decode properly with a soundcard but it can be done if you understand what is going on.

I can say all of this because we have done it. If anyone is interested in our work, which is an analyzer for P25 signals, check out our project at www.sedition.org.au/op25

Cheers,
Matt


The general point of your article is very true - for more scanner users its far easier to just get a scanner with the data output.
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Re: Decoding P25 NSWGRN information

Postby Bigfella237 » Fri Sep 03, 2010 7:45 pm

I knew as I was typing that bit that somebody would probably be correcting me... :oops:

All I can say is that, in my personal experience I have had very little success decoding a P25 CC using a soundcard. And believe me I did try... I must have spent close to a month on and off trying to make it work before I finally gave up and bought my first scanner with CC Dump.

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Re: Decoding P25 NSWGRN information

Postby centralcoastscanman » Fri Sep 03, 2010 9:09 pm

I've got my UBC780XLT hooked up via my soundcard decoding P25 GRN Repeater local to me currently.. initially i had all sorts of problems getting it going as i could get a signal but the soundcard would not recognise it..

all of a sudden one day the friggin thing worked so i am happy, but the signal has to be strong to be able to decode it via your pc's sound card..
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Re: Decoding P25 NSWGRN information

Postby Scotty » Sat Sep 04, 2010 12:51 pm

Thanks for the info Bigfella!

Seems it may be harder for me only having the 996T and 396T, but I'll have a good read through and post any questions to the forum.

Centralcoastscanman - can you advise what program you are using to decode using the 780, and are you using the audio out or a discriminator?

Thanks.
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Re: Decoding P25 NSWGRN information

Postby citabria » Sat Sep 04, 2010 1:58 pm

Hes using Unitrunker and discriminator out. It's impossible to get P25 to decode without a disc tap.
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Re: Decoding P25 NSWGRN information

Postby cartman » Sat Sep 04, 2010 3:45 pm

If you can get your hands on an old second PRO96 (quite often advertised on ebay for a couple of hundred dollars) i found that Andrew Comms at Greystanes carries the data cabling for that model for about 60 odd dollars.
There is a quick four step process to get the data rolling, edit and configure the PRO96.com settings and "bingo" it starts recording + i have a uniden 396 to do voice duties
The issues i have are with PRO96.com is with the UAC settings of Windows 7 - suffice to say that i can't get to record the data permanently - anyway Citabria knows how IT challenged i am


Grant
Professional Scanner nut. Ibis bin chicken of radio scraps
Scanners:
Whistler TRX-1, GRE PSR800 x 2, Uniden 780 x 2, Uniden 796, Uniden 396 x 2, Uniden 246, GRE Pro96.
Software:
DSD v1.101, WinDSDv2, ADCR25 v5.10, Unitrunker, Trunkview
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Re: Decoding P25 NSWGRN information

Postby Sigint » Sat Sep 04, 2010 4:28 pm

Scotty wrote:Seems it may be harder for me only having the 996T and 396T, but I'll have a good read through and post any questions to the forum.

A Discriminator Tap mod can be done to both the 396T and the 996T,
and UniTrunker can be downloaded from www.unitrunker.com.

--
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Re: Decoding P25 NSWGRN information

Postby centralcoastscanman » Sat Sep 04, 2010 8:14 pm

citabria wrote:Hes using Unitrunker and discriminator out. It's impossible to get P25 to decode without a disc tap.


Thanks for that, you are 100% correct.
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