The difference is the use of Frequency Hopping. In Olivia and the other
digital modes, frequency hopping is not used but the data is sent
redundantly over the width of the signal - MT63 is a good example.
From the ROS documentation:
"ROS uses a Spread Spectrum technique known as Frequency-hopping spread
spectrum (FHSS). In a conventional 16FSK system, the data symbols
modulates a fixed frequency carrier; but in a FH/16FSK system, the data
symbols modulates a carrier whose frequency pseudorandomly determined.
In either case, a single tone is transmitted. ROS modulation scheme can
be thought of as a two-step modulation process -- data modulation and
frequency hopping modulation---even thought it can be implemented as a
single step whereby the frequency synthesizer produces a transmission
tone based on the simultaneous dictates of the PN code and the data. At
each frequency hop time a PN generator feeds the frequency synthesizer a
frequency word (a sequence of l chips) which dictates one of 2^l
symbol-set positions. The frequency hopping bandwidth, and the minimum
frequency space between consecutive hops positions, dictate the minimum
number of chips necessary in the frequency word."
I think the FCC rules are more concerned with the encryption aspect of
Frequency Hopping than with the spreading bandwidth, but ROS can be
copied by anyone with the ROS software, so there is a good chance the
FCC might allow ROS on HF in the US, but as it stands right now, the
definition of the ROS modulation scheme classifies it as Spread Spectrum
and Frequency Hopping, and the ROS documentation agrees with the FCC. :-(
73 - Skip KH6TY
Dave Ackrill wrote:
KH6TY wrote:
> All,
>
> If we accept the fact that a SSB transmitter with sufficient carrier
> suppression simply generates an RF carrier equal to the suppressed
> carrier frequency plus the tone frequency (USB), then frequency hopping
> is frequency hopping (spread spectrum), regardless of how the carriers
> are generated.
That's strange, because I see many US Amateurs using modes such as
Olivia and various other data modes...
Dave (G0DJA)
