Advanced Multi Band Excitation
This is the technology that provides the audio compression and decompression for DStar. Seems like a whole lot to take in but we’ve been dealing with audio compression for a long time. Most people have bought and downloaded mp3 or mp4 files. Mp3 or mpeg3 is audio compression technology too.
A typical song is about 3 minutes or 4 minutes long and when uncompressed, it typically is in .wav format and this format can be 5 or 6 times the size of an .mp3 file. So, this .wav format song can be up to 15 to 18 megabytes in its uncompressed size. That would be a lot of data to be streaming or downloading so it is compressed to 3 or 4 megabytes using mp3 compression.
The same principle applies to DStar using the AMBE vocoder (voice encoder/decoder) chip. The chip encodes (compresses) our voice and data into a stream that fits into the 12.5 khz narrow FM signal that we transmit, and when received, the same chip is used in the receiver to uncompress (decode) the signal. What we sacrifice is quality. If we used the same uncompressed audio we expect in an broadcast radio station we would need nearly 3 times the bandwidth when we sum the data with our voice.
The chip is made by a company called Digital Voice Systems Incorporated (DVSI) and is a hardware implementation of audio and data compression compared to a software implementation such as mp3. It is arguable that the hardware implementation is faster and more reliable than a software based vocoder, especially since the DVSI chip has backwards compatibility, is also a analog to digital converter and vice versa, and has even more bells and whistles to fill a couple hundred pages of specifications. So this chip does all of this in one package. That makes the DVSI AMBE chip a good choice for ham radio. We can do all of this stuff on one chip, so it fits nicely into a handy talkie. Everyone knows that hams like HT’s.
I’m not saying that there aren’t other good options out there, I’m not getting into that debate in this article, but many amateur operators choose DStar for a multitude of reasons. I like DStar, DMR, and System Fusion, and the AMBE 3000 chip encodes and decodes them all. It does a good job.
When you buy a DStar radio or a AMBE dongle, or AMBE server you are likely buying the DVSI chip and paying for the license to use that technology. I am certainly glad we have it.
Hosting is relatively cheap for what we do on Ham Radio. A virtual machine, which easily can host a DStar reflector is less than 10 bucks. Even if you have 2 virtual machines running, the costs aren’t bad. When you have 3 instances with backup storage and email hosting and web site hosting, the costs add up quickly.
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I have been experimenting with Allstar nodes and Echolink nodes. A few of our ham friends have been doing excellent work in transcoding and linking Allstar and Echolink into the digital modes (DStar, DMR, Yaesu System Fusion). This is all great stuff and there are some side effects to all of these interconnections.
The symptom that is most recognizable to me is a lag in transmissions reaching all of the intended recipients. We all have noticed that when we transmit, the other side may take a moment to reply. Sometimes this is intentional, sometimes it’s because it takes some time for the message to make it’s way through the network and reach the other side.
It is important that we remember this lag associated with all of these interconnections and adjust the way we key down and key up so that the other end will receive all of what we say. I’m sure you’ve heard someone say their call but you only hear the last 3 letters of their call sign.
The best way to use the network is to key down and wait half of a second to a second before you start talking. The other end will not miss any of your transmission. Also, at the end of your transmission, keep the key down for half of a second when your are through talking so that the other end will hear the very tail of your transmission before you key up.
It is that simple and it makes a world of difference. You should include this technique in your everyday ham radio practices so that everyone hears everything you say.
Thanks for reading! 73