I last looked at this nearly 10 years ago, and had a rather simplistic view of possible modulation schemes.
Was assuming it was either frequency shift keying between two tones using a single carrier (non linear amp ok),?
or one of the schemes using multiple simultaneous carriers (which require a linear amp).
We can do more with a single carrier, and the FreeDV codec has advanced considerably since then.
Guess I should study up!
Jerry, KE7ER
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On Sat, Oct 16, 2021 at 11:10 PM, Tom, wb6b wrote:
On Sat, Oct 16, 2021 at 05:20 PM, Jerry Gaffke wrote:
sending compressed speech slowly to get around that 300 baud thing
I can see your point. If it turns out that the people running D-Star on HF are not pushing the regulation envelope using GMSK modulation, that could mean the possibility of a digital voice HF mode that is compatible with nonlinear RF finals. Then the slow bit rate, buffered, mode would simply be an additional way to extend the DX possibilities for people who really want to do DX and OK with a delay for the purpose.
Switching out the AMBE codec for something like FreeDV or Codec2 would be a good upgrade to a more modern codec (voice encoder) with, from what I've been reading, a two to one improvement in the bitrate needed to transmit the encoded voice.?
