On Nov 25, 2013, at 9:43 AM, Jim N7US wrote:
> For example, while the Report and Order
> mentions RTTY, it also specifies that the signal must be less than 60 Hz
> wide.
I think Jim is right.
Every time the FCC mentions "RTTY," they have always meant "radio teletype."
They don't mean "Steam RTTY." To the FCC, RTTY (radio teletype) simply means
the use of radio to send discrete symbols that are meant for machine decoding.
To the FCC today, 45.45 baud, 170 Hz shift FSK, with Baudot encoding, is just
*one* RTTY mode, not *the* RTTY mode.
I think that we on this reflector (and the ARRL regarding awards) often use the
term "digital" as the placeholder for places where the FCC uses "RTTY."
When translated to human speak, the FCC ruling basically mentions "Digital
modes with shifts of less than 60 Hz." This means that you probably can use
MSK at 45.45 baud, while Steam RTTY is probably questionable. PSK31 also works
since it has no shift.
170 Hz shift FSK keying sidebands fit well within limits of an SSB channel,
especially after it goes through the SSB transmit filter. Nevertheless, the
FCC said 60 Hz, so 60 Hz it is (you can petition the FCC to change that).
Bill: you and I have made one MSK 45.45 baud contact ("23 Hz shift RTTY") in
the past, so you have the software to do it. If not, check out fldigi on
Windows. Or switch any RTTY modem to use 23 Hz shift. 23 Hz shift FSK will be
interoperable (though not optimally demodulating) with the MSK guys.
Just remember to center the Mark and Space of the 23 Hz shift signal around the
1500 Hz point (the 1500 Hz is referenced to the USB suppressed carrier
frequency).
73
Chen, W7AY
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