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by drmpeg 951 days ago
MIL-STD-188-110D defines a 38,400 baud modem at 48 kHz bandwidth. With 256QAM, the raw data rate is 240 kbps.

Of course, the 2.8 kHz bandwidth rule prohibits that in the ham bands. The FCC had originally declined to set a maximum bandwidth in their first ruling, but that caused everyone's head to explode (and that's one of the reasons this ruling has taken so long).

http://tracebase.nmsu.edu/hf/MIL-STD-188-110D.pdf
1 comments
MPSimmons 951 days ago
>The FCC had originally declined to set a maximum bandwidth in their first ruling, but that caused everyone's head to explode

I'm ignorant of what the ramifications would be of this - can you explain why people would have responded like that?

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drmpeg 951 days ago
The HF ham bands aren't very wide. With the exception of 10 meters, from 50 to 500 kHz wide. Folks (including the ARRL) were afraid of abuse. With an SDR, you can generate a signal with any bandwidth you desire.

The reason the FCC didn't want to set a limit is because it's arbitrary. For example, MIL-STD-188-110D (which is an open standard) has a 2400 baud 3.24 kHz mode. But now it's illegal.

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RF_Savage 951 days ago
You mean, still illegal, as it definitely was more than 300baud?

I'd still call this a win. The 300baud limit in USA was keeping the whole field behind by preventimg world wide adoption of more efficient modems.

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drmpeg 951 days ago
Yeah, that wasn't a good choice of words. "It won't be allowed even with the new rules." would have been better.

But I agree. Even with the 2.8 kHz limit, it's still a big step forward.

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