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What is IMBE and APCO 25?

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bigtuna
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What is IMBE and APCO 25?

Postby bigtuna » Wed Sep 10, 2008 10:58 am

Just wondering if anyone could explain the difference between IMBE and APCO 25? As I understand it, APCO 25 is the standard for the digital stream (digital protocol for encoding) and IMBE is the voice encoder (vocoder) for the actual voice message that is enclosed within the APCO 25 stream. If this is true, do all APCO 25 radios use IMBE as the vocoder? I have seen these terms used a lot and I want to understand what they mean. Thanks

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Re: What is IMBE and APCO 25?

Postby Wowbagger » Wed Sep 10, 2008 12:05 pm

viewtopic.php?f=4&t=77951

Summary: You are correct in your understanding. All APCO-25 phase I radios use IMBE for the vocoder. The various phase II contenders: Motorola F2, TIA-Phase 2, as well as the non-APCO25 narrow band protocols like MOTOTRBO, the Kenwood/Icom narrow band protocol, and the various amateur protocols like D-STAR and G4GUO (used by AOR in their digital HF boxes) all use AMBE, which is the successor to IMBE.
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Re: What is IMBE and APCO 25?

Postby bigtuna » Thu Sep 11, 2008 4:15 pm

Thanks for the explanation. I had read that somewhere and was unsure.

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Re: What is IMBE and APCO 25?

Postby W3MOT » Fri Nov 07, 2008 11:33 am

Can AMBE radios communicate with IMBE radios? I'm guessing no.
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Re: What is IMBE and APCO 25?

Postby Wowbagger » Fri Nov 07, 2008 12:13 pm

First of all, please let us NOT use the terms "IMBE" and "AMBE" to refer to a radio. The vocoder is a very small part of what defines a radio. A D-STAR radio is an "AMBE" radio, but will NOT interoperate with a Motorola MotoTRBO or APCO-25 F2 radio (which are both 'AMBE' radios) because the protocol is not the same.

Now, an APCO-25 Phase 2 (TDMA/AMBE) radio (which do NOT exist yet as the standard isn't complete yet) could talk to an APCO-25 Phase I (FDMA/IMBE) radio *in APCO-25 Phase I mode*.

A Motorola APCO-25 F2 (TDMA/AMBE) radio (e.g. the Mackinaw ) could talk to an APCO-25 Phase I (FDMA/IMBE) radio *in APCO-25 Phase I mode*.

A NXDN Radio (FDMA/AMBE) which also implemented APCO-25 Phase I could talk to an APCO-25 Phase I radio.

Do you see a pattern here?

IF a radio implements APCO-25 Phase I then it can talk to another radio that implements APCO-25 Phase I (assuming the radios can operate on the same frequencies, are programmed with compatible NACs and System IDs, etc.).

If a radio does NOT implement APCO-25 Phase I then it cannot talk to a radio that only implements APCO-25 Phase I.

See how much less confusing it is when we USE THE PROTOCOL NAME and NOT THE VOCODER TYPE?
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Re: What is IMBE and APCO 25?

Postby KE7JFF » Mon Nov 10, 2008 10:17 pm

I think you summed it up excellent Wowbanger, but I would describe APCO P25 P1, APCO P25 P2, etc as "container formats" since all they do as provide a way to transport IMBE and AMBE.
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Re: What is IMBE and APCO 25?

Postby mr.syntrx » Sun Feb 15, 2009 2:30 am

Not quite. P25 is a large suite of standards, and not all of them govern what happens over the air interface.

Even referring only to the air interface, P25 provides a lot of air interface services that aren't related to the vocoder at all, e.g. over the air rekeying, call alerts, data transport etc.


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