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P25 Digital Repeater using Motorola Radios

Posted: Tue Dec 20, 2005 4:14 pm
by USGOVTECH
UPDATE:

It is not necessary to do internal mods to Motorola radios to pass P25 data. I discovered that you can use Pin 5 (Flat Tx audio) instead of adding 10k resistor and injecting audio at TXa test point. You can use Maxtrac, CM SERIES, CDM SERIES,SM SERIES, RADIUS SERIES for all radios. Use pin 11 (discriminator) with a 10-20K variable resistor in line between TX and RX you must ground the unused pin of the resistor (You can use pin 7). I am working on a data validation circuit that will allow for only P25 data to be passed thru the repeater if so desired.

PINOUTS

PROGRAM RX RADIO FOR PIN 8 ACTIVE LOW
ALSO PLACE JU551 TO A

RX RADIO TX RADIO
PIN 8 COR DETECT PIN 3 PUSH TO TALK
PIN 7 GND PIN 7 GND
PIN 11 DISCRIMINATOR /\/\/\10-20K VR PIN 5 FLAT TX AUDIO

ADJUST VR for 2.9 to 3.5 Khz of DATA.

Posted: Wed Dec 21, 2005 5:37 am
by motorola_otaku
What's the basis for your P25 validation circuit? I've thought about taking one of the Bearcat BC-i25 scanner cards and trying to derive "P25 COR" from it.

Posted: Wed Dec 21, 2005 6:36 am
by The Pager Geek
I'm going to go out on a limb and say you are doing this with 2 UHF radios? Not crossband....

It should work with a UHF, but a VHF Maxtrac to a UHF maxtrac (Crossband) won't work with this set-up.

tpg

Posted: Wed Dec 21, 2005 7:04 am
by USGOVTECH
As of yesterday afternoon I have used:

2 VHF GM300's
2 VHF MAXTRACS
1 VHF GM300 and 1 VHF MAXTRAC (TX and RX for Both Radio)

The same configuration for UHF Radios

This morning I just tried 1 VHF GM RX and 1 UHF GM TX and it works fine.

Posted: Wed Dec 21, 2005 7:06 am
by USGOVTECH
The validation circuit will be Data detector circuit, it will only validate if digital data is present.

Posted: Wed Dec 21, 2005 12:57 pm
by motorola_otaku
USGOVTECH wrote:The validation circuit will be Data detector circuit, it will only validate if digital data is present.

That's cool, but how? Are you building a circuit from the ground-up, or modifying an existing product?

Posted: Wed Dec 21, 2005 2:24 pm
by The Pager Geek
The VHF Maxtrac to UHF Maxtrac had a problem with one of the receivers inverting the data. (Can't remember which off the top of my head)

I had to either modify the "inverting" receiver, or change where the audio from the Rx's Disc entered the TX Radio.

Just an FYI

tpg

Posted: Wed Dec 21, 2005 4:45 pm
by USGOVTECH
I didnt have to do any mods at all. HMMMMMMMM.

Posted: Thu Dec 22, 2005 5:04 am
by wavetar
Perhaps the GM's were slightly different from the Maxtracs in that respect.

Todd

Posted: Tue Aug 15, 2006 9:41 pm
by MattSR
What is the range and reception like compared to a real Quantar?

Posted: Tue Aug 15, 2006 10:04 pm
by mr.syntrx
Quite a bit worse. A real Quantar regenerates the digital signal - this thing just passes it straight through as it hears it, noise included.

Posted: Tue Aug 15, 2006 10:17 pm
by MattSR
Have you used one of these before or done a back to back comparison?

P25 error detection is pretty damn robust, if a repeater is getting a noisy signal the total BER *should* be the same as if it was working in simplex mode (a la the above repeater). A Quantar can't magically correct uncorrectable errors.

Just interested in how well these things work

Posted: Tue Aug 15, 2006 11:39 pm
by mr.syntrx
Not with P25 specifically, but I've done the same thing with other digital systems.

A Quantar can correct quite a few errors - that's what Forward Error Correction codes are for. When it receives a signal, it will do this, and generate a brand new, clean signal.

This thing, on the other hand, will add noise to what may already be a rather crappy signal if you're trying to hit the machine from the fringes. The signal's journey from the repeater to the receiving radio will then also result in futher deterioration to what may already be a bad signal - whereas from a Quantar, you'd be listening to a fresh, clean, error corrected signal.

Posted: Wed Aug 16, 2006 12:29 am
by MattSR
OK, I see what your saying..

I think it would still make for an interesting project though, if it can get 90% of the performance for 10-20% of the cost then id call it a success, especially if you can use DTMF tones to switch a PL on and off and use it as a conventional HAM repeater too.

Of course, nothing beat a Quantar!

Cheers,
Matt

Posted: Wed Aug 16, 2006 5:03 am
by Wowbagger
MattSR wrote:P25 error detection is pretty damn robust, if a repeater is getting a noisy signal the total BER *should* be the same as if it was working in simplex mode (a la the above repeater).


BER, while a useful end-to-end metric of a signal, is NOT the appropriate measurement to be making here - modulation fidelity is.
Yes - a high BER will cause your signal to fall on its face. But what causes a high BER? It is the radio's inability to distinguish between symbols. And what is the measurement of how "hard" symbols are to distinguish? Modulation fidelity. You will see pretty much the same BER for a 10% modulation fidelity error as you will for a 0.7% error, but if you see a 10% MFE you can know the system is NOT performing well - you have lost most of your margin for decode, and any increase at all in the distortion of the signal will start causing errors.

Think of it as the difference between SINAD and intelligibility - you can have a 20 dB SINAD or a 12 dB SINAD, and still understand what the other guy is saying 100% - but if you are at a 12 dB SINAD coming out of the repeater, any additional noise is going to start causing a whole lot of "What did you say? Say again?" traffic.

The advantage of regenerating the digital signal, even if you don't apply the forward error correction at that point, is that you can go from a 10% MFE to a 0.7% MFE, and thus improve the odds of correctly decoding the signal.

AND, if you then apply the FEC to the signal, you can further clean it up, so that you can once again pick up bit errors without the radio being unable to decode.

Posted: Mon Oct 16, 2006 10:25 am
by f1shs
I've connected to GM950 together, as described on this post.

it doesn't work :-(

My radio is 12,5 kHz channel. Maybe i've a trouble with this kibg of radio ?

please help.

Pierre

Posted: Mon Oct 16, 2006 3:32 pm
by USGOVTECH
The deviation out of the Portable or Mobile must remain the same as it is transmitted thru the repeater this is why the audio adjust pot is required.

Posted: Tue Oct 17, 2006 10:08 am
by f1shs
Hi folks,

I've two GM950 model M08RHH4AN4AN connected together with :

RX pin 8 (CSQ detect - low active) =>>> TX pin 3 (PTT - low active)

RX pin 11 (RX Discri) =>>> TX pin 5 (Flat Tx) trough a 22 k variable resistor

RX pin 7 (GND) =>>> TX pin7 (GND)

I'm using two XTS3000 model H09RDH9PW7BN host R07.09.02 DSP 08.02.04 flashcode 500008-000000-1. Those two radios are configured in 2,5 kHz deviation in ASTRO mixed mode C4FM, low power for lab testing.

The repeater is on the table for lab with a dummy load for TX (433.400 Mhz and no antenna for RX (439.800 MHz).

1) in analog mode, the repeater is working fine. The pot is able to adjust the tx audio.

2) in astro mode, i've got nothing

As i ask before, is it a limitation using a 12,5 kHz TX for repeating ASTRO P25 ?

Pierre

Posted: Tue Oct 17, 2006 10:21 am
by USGOVTECH
The radios may be limiting the Data. Typically the P25 data is 2.83K, The narrow band radios may not work as well.

Posted: Wed Oct 18, 2006 5:30 am
by f1shs
Ok Thank's USGOVTECH ;-)

I'm gonna use a MC2100 with 25 kHz spacing channels capabalities.

As you told, it's probaly a limitation in the RX bacause i'm using a 12,5 kHz spacing radio (regarding the IF).

Keep'n touch.

Pierre

Posted: Wed Oct 18, 2006 6:42 am
by Wowbagger
Make sure that the audio path has as flat a passband response as possible - take the audio directly from the detector, and route it as directly to the modulator as possible.

Remember that many radios have either a C-weighted audio response, or some other bandpass response. *ANY* non-flat frequency response will KILL the APCO-25 waveform - drive the intersymbol interference through the roof, and make your modulation fidelity error HUGE.

Can you get access to something that can measure P25 modulation fidelity (and it's pretty obvious what I'd recommend...) - if you can actually get something that can show you the eye diagram or modulation fidelity that would really help you identify the problem.

Posted: Sun Oct 22, 2006 8:30 am
by f1shs
it work's !!!

I've change the RX radio for a 25 kHz spacing channel capable, and it's works very fine ;-)

We've looked at the TX deviation to be in the limit of 3 kHz.

So i anderstand now that you need a pair of 25 kHz radio to make the P25 repeater become a true story ;-)

many thank's to all of you.

Now we have the first P25 repeater in Paris.

Pierre

Posted: Sun Oct 22, 2006 9:37 am
by USGOVTECH
Yes that is correct. Great to hear that it works. The Dev should be around 2.83 khz +/- a few hz.

Posted: Wed Nov 15, 2006 7:35 pm
by mancow
I just got one working (in band) Uhf using an HT600 as the RX radio and a Bendix King LPU as the TX unit.


Smooth...... 8)

P25 ADP AlgoID

Posted: Thu Aug 07, 2008 5:09 am
by MattSR
Hi guys,

Does anyone with a P25 service monitor here know the AlgoID for ADP? Ive discovered some common algos in P25 training docs and whatnot, but the value for ADP escapes me, and I dont have a 2975 to check it with :)

Discovered some more AlgIDs (but not ADP sadly)

Heres the values that I have found (from publicly available docs on the net)

0x00 Accordion 1.3
0x01 BATON (Auto even)
0x02 Firefly
0x03 Mayfly
0x04 Saville

0x41 BATON (Auto Odd)

0x80 Clear
0x81 DES-OFB
0x82 2 key Triple DES
0x83 3 key Triple DES
0x84 AES-256

0x9F DES-XL
0xA0 DVI-XL
0xA1 DVP-XL

Re:

Posted: Wed Jul 29, 2009 5:53 pm
by MattSR
Hi wowbagger,

Its only taken me three years to digest your post - but yes you are quite right, I've learned a fair bit since I made my original post, and thanks for the explanation - it has pointed me i the right direction :)

Cheers,
Matt

Wowbagger wrote:
MattSR wrote:P25 error detection is pretty damn robust, if a repeater is getting a noisy signal the total BER *should* be the same as if it was working in simplex mode (a la the above repeater).


BER, while a useful end-to-end metric of a signal, is NOT the appropriate measurement to be making here - modulation fidelity is.
Yes - a high BER will cause your signal to fall on its face. But what causes a high BER? It is the radio's inability to distinguish between symbols. And what is the measurement of how "hard" symbols are to distinguish? Modulation fidelity. You will see pretty much the same BER for a 10% modulation fidelity error as you will for a 0.7% error, but if you see a 10% MFE you can know the system is NOT performing well - you have lost most of your margin for decode, and any increase at all in the distortion of the signal will start causing errors.

Think of it as the difference between SINAD and intelligibility - you can have a 20 dB SINAD or a 12 dB SINAD, and still understand what the other guy is saying 100% - but if you are at a 12 dB SINAD coming out of the repeater, any additional noise is going to start causing a whole lot of "What did you say? Say again?" traffic.

The advantage of regenerating the digital signal, even if you don't apply the forward error correction at that point, is that you can go from a 10% MFE to a 0.7% MFE, and thus improve the odds of correctly decoding the signal.

AND, if you then apply the FEC to the signal, you can further clean it up, so that you can once again pick up bit errors without the radio being unable to decode.

Re: P25 Digital Repeater using Motorola Radios

Posted: Mon Aug 03, 2009 8:03 pm
by newtomotorola
Sorry to digg up an old thread, but what are people's recommendations on UHF versions that would do this say around the 420-450 area

Thanks

Re: P25 Digital Repeater using Motorola Radios

Posted: Tue Aug 04, 2009 6:18 pm
by Astro Spectra
The $64,000 question was "What's the basis for your P25 validation circuit?". Well, perhaps the answer might be found here:

http://nicta.com.au/__data/assets/pdf_f ... ware_1.pdf

Now before anyone starts going on about DVSI (and other's) patents notice that this project was to convert P25 RF received off air to digital data displayed on PC and it wasn't intended as a saleable product.

Well it turns out that this project was based on the GNUradio free software development signal processing toolkit. You can do further reading here:

http://sedition.org.au/op25/wiki/WikiStart

and

http://gnuradio.org/trac/wiki

plus a cool 4FSK software demod plug in from:

http://radiorausch.googlepages.com/Gnur ... elFSK.html

BUT and it's a big BUT, this is a major major project with good C++ skills required. It is hardly ‘batteries not included’, it’s not ‘some assembly required’, and it’s certainly not 'plug and play' like Unitrunker.

Well actually a whole lot of assembly is required and while it looks like the transmit functions are still a bit primitive, these Australians look pretty serious.

Note also that the implementation is done via sampling either the RF or IF rather than by means of a discriminator tap (although that is certainly possible). The whole software-defined radio thing looks a bit overly complex and expensive when using the typical USRP front end when most people here would be able to lay their hands on suitable RF decks but Max KA1RBI has done a simple 455 kHz to sound card IF design is here:

http://www.lightlink.com/mhp/iq/

So the whole "P25 validation circuit" is going to look like a small PC server.

Oh, and here's the thing - you're not going to be trying to sell this as a commercial product because while you don't need an IMBE decoder for a repeater you will still be using all sorts of IP that belongs to others...

Re: P25 Digital Repeater using Motorola Radios

Posted: Tue Aug 04, 2009 10:53 pm
by MattSR
We are very serious - this is part of Steve Glass's Comp Sci Phd thesis, so we clearly aren't mucking around.

At the moment testing is underway on pure I/Q decoding as opposed to Franks C4FM slicer.

Astro Spectra wrote:So the whole "P25 validation circuit" is going to look like a small PC server.

Oh, and here's the thing - you're not going to be trying to sell this as a commercial product because while you don't need an IMBE decoder for a repeater you will still be using all sorts of IP that belongs to others...


Why? without IMBE I cant see anything in a P25 repeater that's proprietary or IP...

Re: P25 ADP AlgoID

Posted: Thu Aug 20, 2009 5:35 am
by MattSR
Well. I finally found it - I've succesfully captured the data using the OP25 project and GNUradio framework and it all decodes perfectly!

The AlgID is 0xAA.

Its sad that 90% of the people that look at this post won't understand the significance of what has been achieved with this project, but here it is anyway :)

Image
Image
Image

Re: P25 Digital Repeater using Motorola Radios

Posted: Thu Aug 20, 2009 5:40 am
by MattSR
Thanks to Max, KA1RBI, some more progress has been made on OP25.

I used a Ubuntu running inside VMware, and a disc tapped uniden scanner to create the following screenshots:-

The first one shows a grab of an ADP transmission, the second shows the output of the C4FM slicer (work continues on a I/Q decoder that handles both CQPSK and C4FM)

Image
Image
Image

Cheers,
Matt

Iiiinnnntersssting!

Posted: Thu Aug 20, 2009 5:43 am
by Wowbagger
Very interesting. Thanks for posting this.

Re: P25 ADP AlgoID

Posted: Thu Aug 20, 2009 5:56 am
by MattSR
No worries - All that was used is Ubuntu running in VMware, and a discriminator tapped Uniden scanner..

There are other things coming too :)

Re: P25 ADP AlgoID

Posted: Thu Aug 20, 2009 6:57 am
by escomm
Cool

Re: P25 Digital Repeater using Motorola Radios

Posted: Thu Aug 20, 2009 2:12 pm
by The Pager Geek
Lookin Sweet

Re: P25 ADP AlgoID

Posted: Thu Aug 20, 2009 2:53 pm
by newtomotorola
Hi Matt, mabie you could post up a step by step on how to get it working through vmware. I think what you guys are doing is fantastic, keep up the good work.

Cheers

Re: P25 ADP AlgoID

Posted: Thu Aug 20, 2009 3:03 pm
by MattSR
No worries, I need to update the wiki with some doco on how to do it.

I used VMware Fusion on a Mac, though it shouldn't be too hard to get it running on other platforms.

Re: P25 Digital Repeater using Motorola Radios

Posted: Thu Aug 20, 2009 4:34 pm
by newtomotorola
Thanks mate highly appreciate it, would love to get it going and having abit of a play.

Re: P25 Digital Repeater using Motorola Radios

Posted: Mon Nov 30, 2009 8:37 pm
by MattSR
Back on the topic, transmit code has been added to OP25. One step closer to a software defined repeater. :)

Re: P25 Digital Repeater using Motorola Radios

Posted: Fri Jun 17, 2011 12:41 pm
by kb9suy
Has anyone been able to do a cross band with gm300's succesfully? I can pass VHF to UHF Can not pass UHF to VHF any luck.