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Humans are asynchronous receivers, they can pick up words at any time, even if spread out, can combine into a sentence. Data rates are as fast as someone can hear/talk/copy code.

All of the fast digital modes are Synchronous, example the HF digital voice has a lag between someone talking and their voice getting out because of the initial sync code.

On a particular radio Wikipedia page, it claimed these data rates:

AM/FM Synchronous: 12/16 kbit/s

AM/FM Asynchronous: Below 4800 Baud

What aspect of digital technology allows the data rate to be much faster if the transmission is synchronous.

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  • $\begingroup$ Looks like it is an expensive radio. $\endgroup$ – K7PEH Nov 11 '14 at 16:53
  • $\begingroup$ I don't even think it is for sale other than the military $\endgroup$ – Skyler 440 Nov 12 '14 at 4:31
  • $\begingroup$ Oops, sorry about that, I found it on the Wikipedia page for the radio. Edited to add the correct link. Where I found the data rate information. $\endgroup$ – Skyler 440 Nov 17 '14 at 22:56
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Wikipedia is plain bonkers. The manufacturer's data sheet is more enlightening:

Waveforms/Modes of Operation

Implemented and Planned

  • AM/FM
    • Non-secure voice
    • Non-secure narrowband voice (FM)
    • 12 and 16 kbps secure voice
    • 12 and 16 kbps secure synchronous data
    • Secure asynchronous data to 4800 bps

[...]

  • ANDVT
    • Secure narrowband voice (LPC-10, MELP Vocoders)
    • Secure 2400 bps synchronous data

Notice it says "bps" and "kbps" which mean "(kilo) bits per second". There is no "baud" anywhere in the spec sheet. Whoever wrote that Wikipedia article must not know the difference.

Secondly, we can't infer from any of this that synchronous communications are faster than asynchronous communications. All we can infer is that this particular radio implements a number of modes. Some are fast, and some are slow. Some are synchronous, and some are asynchronous. You can even see that the slowest data listed in the datasheet is ANDVT, and it is described as "synchronous".

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