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  #1 (permalink)  
Old 03-16-2008, 8:53 PM
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Default DV Dongle AMBE Codec: Potential

I'm wondering if anyone has heard of this thing called the DV dongle. It can be found here: http://www.moetronix.com/dvdongle/

It's avaliable for purchase here: http://www.hamradio.com/ for $200. It seems that it's basically just an AMBE-2020 chip with USB controller that plugs into your PC and can allow you to decode AMBE (and presumably IMBE) using some provider driver software and code.

It's a cool idea considering that DVSI has pretty tight control on any software implementations of their codecs and thus far has made it impossible to really get much aside from some developer boards - no real end-user codec stuff. This appears to be a simple workaround that allows for coding and decoding with a PC.

It's aimed at D-Star but it mentions that it has other uses. I'm wondering how hard it might be to use this as the implementation for decoding things like Opensky, Provoice, P25 and even possibly stuff like inmarsat.

Considering most of these use standard modulation and just basic TDMA, it doesn't seem like it would be beyond the relm of possibility.
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Old 03-16-2008, 9:20 PM
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Sounds like a neat idea but experimentation and innovation like that is pretty much dead since anything short of sitting on the couch watching TV is illegal with all the copyright law running around out there.


Quote:
Originally Posted by kb1ipd
It's aimed at D-Star but it mentions that it has other uses. I'm wondering how hard it might be to use this as the implementation for decoding things like Opensky, Provoice, P25 and even possibly stuff like inmarsat.
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Old 03-16-2008, 10:00 PM
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Moetronix is the company that writes the software for the RFSpace SDR-14, which is an outstanding piece of equipment for spectrum analysis and other uses. I expect this will be a quality device as well. Very interesting. Thanks for the info.
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Old 03-17-2008, 10:45 AM
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Quote:
Originally Posted by mancow
Sounds like a neat idea but experimentation and innovation like that is pretty much dead since anything short of sitting on the couch watching TV is illegal with all the copyright law running around out there.
The Am-2020 chip is acquired legally for the purpose of use in radio communications applications. There's no misuse of software code or anything because it's hardware. Last I checked, monitoring unencrypted radio communications of public safety and such is perfectly legal.

Why do you think this is going to be a problem?
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Old 03-17-2008, 12:48 PM
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I was thinking in terms of Opensky or Inmarsat. I'm sure it's just fine for its intended purpose. I just figured that the way DVSI is and everyone else these days there is probably something somewhere that prohibits its use for anything else.

As for the technical side, I wonder how it could be applied to other applications. The AOR HF modem had me thinking along the same lines. It too uses an AMBE chip just like this thing.

Being that IMBE and AMBE are two different things I wonder how this box could be made to decode IMBE. Is the AMBE chip backward compatible and capable of dedoding IMBE or would it need some sort of software loaded...?

If it was something that could be used for IMBE or even AMBE with Inmarsat or whatever else it would be worth buying to play around with.
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Old 03-17-2008, 12:58 PM
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IIRC AMBE is downward compatable for decoding IMBE. Yes, I think inmarsat could be legally iffy, but I'd think opensky would be fine if it's unencrypted. Inmarsat might be okay based on the bill in the 1980's that spessified unencrypted/nonsecure satellite stuff is fair game but breaking any protection systems especially for security is not. But then again, it might be considered a "mobile phone" which is a special case for scanning.
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Old 03-18-2008, 6:32 AM
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Wink These work very well.

I have a couple friends that have the DV-Dongles and they work very well on D-Star.
Here in Connecticut, we are very lucky to have 6 D-Star repeaters up and running on both VHF and UHF.
These dongles are nice in that they allow you to sit at your computer and monitor any gateway connected d-star repeater wherever it is located.
The digital audio on these are very nice also.
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Old 03-18-2008, 9:49 AM
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Hello,

I was looking at the AMBE chips a couple of years ago and wondered if I could interface it to a PC and decode DStar and P25. It looks like someone did the heavy interface work for me.

From my understanding of P25, a PC decoding program would have to assemble 20 mS voice frames from the P25 frames and format it to the AMBE 2000 frames by adding the additional mode bits, etc. Ship them off to the USB device and get audio back.

The interface API looks like it is based on the RF Space SDR devices.

I think I will order one to play with. Thanks.

73 Eric
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Old 03-18-2008, 11:27 AM
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"ProVoice will fall to hobbyists' wrecking ball"

I don't know why I thought of that--
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Old 03-18-2008, 12:09 PM
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Quote:
Originally Posted by EricCottrell
Hello,

From my understanding of P25, a PC decoding program would have to assemble 20 mS voice frames from the P25 frames and format it to the AMBE 2000 frames by adding the additional mode bits, etc. Ship them off to the USB device and get audio back.
Considering the power of today's PC's I don't think that would be a big problem. It's just an issue of getting the signal into the PC to do that. I *think* a good sound card would be capable from the discriminator of a suitable radio receiver.

Otherwise maybe some kind of ADC or SDR connected to the IF would work.
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Old 03-18-2008, 4:53 PM
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Quote:
Originally Posted by kb1ipd
Considering the power of today's PC's I don't think that would be a big problem. It's just an issue of getting the signal into the PC to do that. I *think* a good sound card would be capable from the discriminator of a suitable radio receiver.

Otherwise maybe some kind of ADC or SDR connected to the IF would work.
Hello,

We have programs that can decode 9600 baud P25 control channels from a discriminator tap and voice is just another frame type. This will be a good use of a stereo line in with the control channel on one line in channel and voice channel on the other line in channel.

The fun part is decoding the protocol and getting it into the proper format for the AMBE chip. I remember that the FEC (Forward Error Correction) part of the P25 voice frame is done by the AMBE chip so the PC just needs to do the upper level error correction.

I briefly looked at the ProVoice format a year or so ago and it appears to be similar to the EDACS control channel format. It uses a different preamble. The important bits are transmitted three times with the second time inverted just like the control channel. There are additional "unimportant" bits at the end that are just transmitted once. In P25 there are also "unimportant" bits that are not protected by FEC. This is the reason P25 tends to sound robotic on weak signals. I do not know if the ProVoice stream has FEC or not but the end result seems to be a similar data stream fed to the IMBE chip as P25.

I ordered one and it is being shipped ground out of Atlanta so it will take a few days. I suspect it will be a few weeks before I can figure out if this can decode P25. We have a local DStar Repeater so I could always use it for DStar if it does not decode IMBE.

73 Eric
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Old 03-18-2008, 5:51 PM
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Neat stuff!!

Thinking out loud here and I may not be understanding it all but what if a receiver like AOR that went up to 1500 mhz had its IF tied to another like the 2096 and then the I/Q data was tapped off the inside of the 2096. Does that even make sense...?

I ask because I sucsessfully tied my AOR300A to my 2096 through one of the IF stages by physically linking the RX port of the 2096 to that stage of the 3000A. I can't remember the exact frequency but it was somewhere around 300 Mhz that the 2096 needed to be tuned to. When the 3000A was tuned to a P25 frequency the audio came out of the 2096 perfectly. I was bored and I wanted to see how easily radios could be cascaded that way and it worked perfectly. It's a rough way of downconverting but if that module could somehow be "placed in line" with or instead of the IMBE chip would it decode? What about differing data rates?

Last edited by mancow; 03-18-2008 at 11:02 PM..
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Old 03-19-2008, 12:11 PM
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Quote:
Originally Posted by mancow
Neat stuff!!

Thinking out loud here and I may not be understanding it all but what if a receiver like AOR that went up to 1500 mhz had its IF tied to another like the 2096 and then the I/Q data was tapped off the inside of the 2096. Does that even make sense...?

I ask because I sucsessfully tied my AOR300A to my 2096 through one of the IF stages by physically linking the RX port of the 2096 to that stage of the 3000A. I can't remember the exact frequency but it was somewhere around 300 Mhz that the 2096 needed to be tuned to. When the 3000A was tuned to a P25 frequency the audio came out of the 2096 perfectly. I was bored and I wanted to see how easily radios could be cascaded that way and it worked perfectly. It's a rough way of downconverting but if that module could somehow be "placed in line" with or instead of the IMBE chip would it decode? What about differing data rates?
Hello,

I remember that was done to confirm the 380 MHz P25 system I found at Walter Reed. The Pro96 is deaf at 380 so someone used another radio as a front end and used P96Com to decode the control channel.

The DV Dongle only interfaces over USB so at some point the analog signal has to be converted to digital. The setup is more like using the RF Space SDR-IQ connected to the 3000A. You take the digital stream from the SDR-IQ and use a program on the pc to demodulate the digital stream and convert to the AMBE2000 data frames. You can not get around needing code on a PC to do the conversion and control.

73 Eric
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Old 03-25-2008, 3:15 PM
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Hello,

I got the DV Dongle. Neat device.

There is sample code on the web site that was used for testing. I am going to modify it to try the P25 rate. I mapped out the P25 Voice format and it appears I could do a voice only program with little frame decoding and error checking in a few days. This is only a proof of concept to see if IMBE can be decoded by the AMBE2000.

73 Eric
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Old 03-26-2008, 4:24 PM
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Default DV Dongle AMBE Codec

You mentioned the DV Dongle, available for $200. As you probalby know, it's a way to connect to the
D-STAR network without a D-STAR radio. Have you seen the article on page 89
of the April 2008 CQ magazine about the DV-Dongle?

In my opinion, it's too bad the D-STAR is "almost open" and not completely open. The
AMBE Codec is
copyrighted, and requires a license to use it. As a software developer, I could
theoretically write a program for my PC that would do the same thing as the
DV-Dongle (without the $200 cost). Unfortunately, as I understand it, it would be a violation of the
Codec copyright for me to write and use this program. All this assumes that the AMBE Codec
copyright holder would make available the details of how the Codec works (which
they surely won't). The rest of f D-STAR protocol is already available publically, I think.

Does anyone know why the Japan amateur radio group that originally thought up D-STAR
made it "almost open" by choosing a copyrighted Codec, rather than choosing an
open Codec? I sure would like to see a completely open digital voice and data
standard become popular, so that anyone who wished could implement it in hardware
or software without fear of copyright infringement.
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Old 03-26-2008, 5:46 PM
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Hi Eric,

I believe your POC will work just fine. I found this excerpt in the Daniel's P25 Training guide which seems to suggest that IMBE and AMBE are compatible.. I have also read the AMBE frames will still decode fine when fed into an IMBE vocoder, just the extra features and quality are lost.

Quote:
DVSI has also introduced new Enhanced Vocoders for P25 based
on DVSI’s latest AMBE+2™ Vocoder technology. The Enhanced
AMBE+2™ Full Rate Vocoder is fully interoperable with the current
P25 7.2 kbps (IMBE™) standard. The AMBE+2™ can also operate at
half rates of 3.6 kbps for Phase 2. The AMBE+2™ provides improved
voice quality, better noise immunity, tone capability, and other new
features. The Enhanced Vocoders significantly improve the voice
performance of the P25 system, while facilitating the migration and
interoperability between new and existing P25 equipment.
DVSI’s
vocoder technology is used extensively in digital radio systems and in
mobile satellite telephony worldwide.
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Old 04-01-2008, 5:37 PM
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Quote:
Originally Posted by EricCottrell
Hello,

I got the DV Dongle. Neat device.

There is sample code on the web site that was used for testing. I am going to modify it to try the P25 rate. I mapped out the P25 Voice format and it appears I could do a voice only program with little frame decoding and error checking in a few days. This is only a proof of concept to see if IMBE can be decoded by the AMBE2000.

73 Eric
U would love to hear. I emailed DVSI about the capability of the AMBE2020 to decode IMBE and they asked me about the context at which point I said that I was working on a decoder for APCO P-25. Their response was "Not of that format. That was a purpose-designed solution."

I'm not sure if I completely believe that based on the context. It might be that the voice would need to be separated as frames. DVSI tends to not be so helpful in anything that might reveal a client's system or anything like monitoring their communications.

So I'd be looking very forward to finding out about this.

Of course, even if it doesn't work, it might still be useful for something like Opensky
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Old 04-02-2008, 12:53 PM
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Doing some research I've found the AMBE2020 can't decode an APCO P-25 stream by itsself. No surprise there. One would need to feed it just the speech data and do the demodulation and frame extraction, because it's strictly a codec chip.

However, I've seen a bunch of posts (although it seems anecdotal) which say that it will decode a standard IMBE stream. I have seen this on newsgroups and such. On one it stated that all AMBE decoders are downward compatable with IMBE and that IMBE decoders are "semi-compatible with AMBE, but will not give the quality improvements and might not work at some bit rates"
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Old 04-02-2008, 6:32 PM
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Hello,

I am still working on a P25 decoder. I managed to spend over a week finding out my AR5000 does not pass the P25 waveform cleanly. 9600 baud EDACS is no problem with the AR5000. It appears there is too much level shifting of the waveform for a clean P25 decode. There is some circuity in the AR5000 between the Discriminator Output and the Demod Output. There is a mod to tap directly off the Discriminator Output. With the bad output I could not get a good decode of the sync bits and data clock recovery did not work well.

I tried my WinRadio G305e today as a test and the waveforms look a lot better. I still need to feed it through the decoder and see if I can get good decodes. Back to Square One.

73 Eric
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Old 04-02-2008, 6:58 PM
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Interesting, keep us updated please!
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