AA6YQ comments below
From: RTTY [mailto:firstname.lastname@example.org] On Behalf Of Kai
Sent: Thursday, December 26, 2013 3:16 PM
Subject: Re: [RTTY] Wow - thanks Dr Flowers!
Baud rate does NOT limit BW, except for 2-tone FSK RTTY.
Actually, two tone FSK RTTY is the ONLY digital modulation that currently has a
defacto BW limit under FCC rules. Those limits are
300 baud and 1000 Hz maximum spacing between tones, which would occupy 1500 Hz.
No one uses that, but it is a limit.
On the other hand, I can legally use, for example, 16 carriers (or 32 or 64)
spaced 1 kHz each, with each carrier containing QAM
encoding, and as long as I strobe the ensemble of those carriers at less than
300 baud, I'm legal - and occupying more than 18 kHz
(or 34kHz or 66 kHz) BW. It's a crappy modulation but LEGAL today! The FSK
shift limit doesn't apply because it's not FSK!
The ONLY thing limiting modulations like the crappy ones I listed above is that
VERY FEW receivers out there can handle a bandwidth
of 18 kHz (or 34 kHz or more). Most radios can handle less than 2400 Hz of
phase and amplitude-linear BW suitable for modern
Thus in the real world, where HF transceiver passbands have finite widths,
baud rate limits bandwidth.
PACTOR-4 (which occupies about 2200 Hz BW, just like PACTOR 3 which is in use
today) would indeed be permissible once the 300 baud
symbol rate is removed.
If the ARRL petition is accepted, Pactor 4 would only be permissible if it is
publicly documented as the ARRL describes here:
" Documentation should be adequate to (a) recognize the technique or protocol
when observed on the air, (b) determine call signs of
stations in communication and read the content of the transmissions."
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