When the FCC uses the term of the same modulation type, that would be
the first symbol of the ITU Emission Classification system or the main
carrier modulation. Thus, if you are using SSB as the primary
modulation then you are limited to what is considered a communications
quality signal. As amateur practices have improved over the years, this
is quite narrow, often not a lot more than 2000 Hz depending upon the
transmitter.
Needless to say, modes wider than communications quality are not
permitted by the FCC on most of the HF bands since the whole point is to
use amateur radio friendly modes that are spectrum efficient. The FCC
requires that we use good amateur practice as our guide.
Further, most of us are also going to also take into consideration and
abide by the IARU Region 2 Band Plan which does not allow any modes
wider than 2700 Hz below 29.000 MHz in the RTTY/Data portions of those
bands.
Before the advent of multitone modems, we had 2 tone FSK modems.
Initially, the spacing of the mark and space tones was as much as 850
Hz. As technology improved, ham friendly technology allowed the
reduction to narrower shifts and is now typically 170 Hz with a few
modems using 200 Hz. But the intent for the maximum 1000 Hz shift was
clearly to keep the bandwidth narrow.
After the development of many multitone modes, the FCC reinterpreted the
rules to consider the baud rate of an individual tone, rather than
overall baud rate. This means that single tone modems such as
MIL-STD-188-110A are illegal to use in the U.S. RTTY/Data portions
because they use 2400 baud at all times, independent of the actual data
rate throughput. They may possibly be legal to use in the Phone/Image
portions. Several of us have asked for clarification from the FCC and
have been stonewalled repeatedly for quite some time.
Multitone modems that use FSK typically have the tones separated by a
small number of Hz and are therefore legal as long as any individual
tone does not exceed 300 baud, therefore we can use modes as wide as a
communications quality phone transmission in the RTTY/Data portions
according to Part 97.
We are limited by the transceiver capabilities since some are hard
pressed to even do 2000 kHz, but with DSP and other modified equipment
the passband can be greatly extended. The 2700 Hz maximum allowed under
the IARU Band Plan recommendation seems about as wide as any ham
friendly mode should be operating. Even then this should only be used
under unusual circumstances and on a band that is not busy with other
signals.
Final thought ... just because you can do something, does not
necessarily mean you should be doing it.
73,
Rick, KV9U
Tooner wrote:
--- In digitalradio@yahoogroups.com, Rick W mrf...@... wrote:
... There is no conflict with using wide modes (FCC defined as up
to the bandwidth of a communications quality phone transmission)
as long as the baud rate of an individual tone does not exceed
300 baud.
Hey Rick. Thanks for the reply!
I think the confusion I have with quality phone transmission comment is the
part that says ...of the same modulation type.
And you say the individual tone, but I read symbol rate in the regs. Can
an individual tone have a baud rate? I thought the rate was how fast the
tones were being sent, like a computer modem. Or, are both quotes meaning
the same thing?
From what I understand, let's say, in the 20 and 40M sub-bands, the maximum
width for a signal is 1000 wide, not as wide as phone TX. That's found
under § 97.305 Authorized emission types.
It says 20 m 14.00–14.15 MHz, RTTY, data, and refers to (3) of § 97.307(f),
which says: The symbol rate must not exceed 300 bauds, or for
frequency-shift keying, the frequency shift between mark and space must not
exceed 1 kHz.
Reason I ask, and I'm sorry if I sound dense, is it legal to transmit on the
digital modes sub-bands modes that are greater than 1000 wide, like Olivia
2000? Some modes can easily be 3000 wide, but still narrower than phone
communications.
I've not really been able to get an answer that confirms the question:
Assuming it's in a band or sub-band that digital modes are authorized, can
we operate digital modes that are wider than 1k?
Thanks for the help and input!
f, k2ncc
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