Wednesday, November 12, 2008

Dongle, dongle everywhere

I see a good deal of traffic looking for information about DVSI's AMBE and IMBE vocoders.  Not surprising; these vocoders are at the heart of D*STAR and APCO 25 (respectively), and I've blogged about both before (APCO 25/IMBE here, D*STAR here).  As D*STAR is becoming increasingly popular with hams, and APCO 25 is increasingly widely deployed in public service radio, it's not surprising that people are looking for ways to decode these signals.

Unfortunately, they're not going to find it.  DVSI refuses to release much information about their vocoders, and virtually everyone using them is using the DVSI-provided DSP chip, which has been readlocked so you can't suck the program out of it.  I haven't heard of anyone selling an IMBE dongle in the end-user market, although there may be IMBE add-on devices for some scanners; check with your manufacturer.  For AMBE, there is the "DV Dongle", a USB dongle that contains a DVSI AMBE chip.  In theory, it should also be possible to cannibalize an AMBE or IMBE chip from a radio that had one and interface it; there should be enough information in the market to do that, at least, especially since reportedly both chips are standard DSP chips with known interfacing characteristics.  There are also reports of AMBE and IMBE boards for use in a PC, but at very high prices ($1000 and up).

The tightly controlled trade-secret status of these decoders makes it impossible, of course, for a third party to write a compatible codec.  This is, of course, deliberate by DVSI; they have a captive market and they'd like to keep it that way.  IMBE's widespread adoption within APCO 25, which is all-but-mandatory in public service now gives them a lucrative cash cow, much of which comes from Department of Homeland Security grants to improve national readiness in the event of terrorist attack.  Just how much economic rent is being paid (mostly by taxpayers) to DVSI for this monopoly?

(Updated to correct AMBE/IMBE confusion.  Sorry about that.)