It will be spread spectrum if the tone frequencies are controlled by a
code as explained in the ROS documentation:
"A system is defined to be a spread-spectrum system if it fulfills the
following requirements:
1. The signal occupies a bandwidth much in excess of the minimum
bandwidth necessary to send the information.
2. Spreading is accomplished by means of a spreading signal, often
called a code signal, which is independent of the data.
3. At the receiver, despreading (recovering the original data) is
accomplished by the correlation of the received spread signal with a
synchronized replica of the spreading signal used to spread the information.
Standard modulation schemes as frequency modulation and pulse code
modulation also spread the spectrum of an information signal, but they
do not qualify as spread-spectrum systems since they do not satisfy all
the conditions outlined above.
Note that all three conditions must be met to be considered spread
spectrum. I don;t know if it would be possible to send the data in less
bandwidth, but, for example, PSK31 accomplishes the same typing speed in
a bandwidth of 31 Hz, instead of in 2000 Hz, so ROS is probably truly
spread-spectrum.
Remember that spread spectrum was conceived as a way of coding
transmissions so they could not be intercepted and decoded. In fact
actress Hedy Lamarr invented spread spectrum, and you can read that
here: http://en.wikipedia.org/wiki/Hedy_Lamarr. The difference is the
use of a code to spread the data and signals to avoid detection and
monitoring by those without the same code.
Download the documentation from www. rosmodem.wordpress.com and read
about spread spectrum and the ROS implementation. That will make it
clear I think. Remembering that a single tone creates a single RF
carrier makes it easy to see how just about anything can be done with
tones, including sending data over several tones at once so if one
carrier is lost, others carry the same data, or using a psuedo-random
code to determine the carrier frequencies, as I think is done in ROS.
That documentation also explains the difference between FHSS and modes
like MFSK16. However, a main point is that the data does not have to be
scattered over such a wide bandwidth to achieve communication, but ROS
does, so it qualifies as spread spectrum.
If you have a receive bandwith of 10,000 Hz, and you spread over that
bandwidth, you really are using way more bandwidth than necessary to
send the same data at a given speed. MT63 uses 64 carriers with the data
divided among the carriers for redundancy and about 40% of the signal
can be obilterated by QRM and still produce good copy. I think the
difference with ROS is that the carrier frequencies are varied according
to a code, instead of being at a fixed position, but I am no expert on
modes, so someone else can probably explain it better and with more
accuracy.
Generally it is qualifies as spread spectrum if a code is used for the
spreading, and in military communications (and even cell phones, I
think) the code prevents anyone else from reconstructing the signal so
that the intelligence can be recovered if they do not possess the same code.
73 - Skip KH6TY
John wrote:
Thanks Skip,
Unfortunately, this really does not get to the crux of my question(s).
I understand how an SSB transmitter works, but that is not really what
I am after.
What I am driving at is if like this. If I use DM780 to run some
version of digital mode via an SSB transceiver, it uses a tone or
series of tone modulation/shifting to create the output of the
transmitter, and not one single mode is called "spread spectrum"
output, but is called FSK or PSK, etc. Now, we get into the
aforementioned discussion regarding ROS, and suddenly, still via the
microphone input of the same transmitter, those shifted frequencies
are now called "spread spectrum" instead. I am having a great deal of
difficulty understanding, other than the author happened to call his
scheme "spread spectrum" in his technical documentation.
Thanks ....
John
KE5HAM
--- In digitalradio@yahoogroups.com
<mailto:digitalradio%40yahoogroups.com>, KH6TY <kh...@...> wrote:
>
> John,
>
> Given sufficient carrier suppression, any tone inputed to the
microphone
> makes the transmitter output a pure RF carrier at a frequency of the
> suppressed carrier frequency plus the tone frequency for USB, or minus
> the tone frequency for LSB. Whatever you do with the tones determines
> what RF carriers come out. You can key the tones, or shift the tone
> frequencies, etc., and the RF output will follow. The ARRL Handbook
> usually has an explanation of this.
>
> Hope that answers the question.
>
> 73 - Skip KH6TY
>
>
>
>
> John wrote:
> >
> >
> > So as to not continue growing the ROS legality discussion even
> > further, I would like to ask a fairly simple question.
> >
> > How will the modulation be determined from any SSB transmitter when
> > the source of the modulation is via the microphone audio input of
that
> > transmitter?
> >
> > Simply stated, how would any digital mode create anything other than
> > some form of FSK simply by inputting a tone at the microphone input?
> >
> > Regardless of the software being used to generate the tone(s), at any
> > given time there is nothing more than the absence or presence of a
> > tone at the audio input of the transmitter. This is true of HRD's
> > DM780, MixW modes, MMSSTV, or many other sound card driven software
> > packages. They all have one thing in common, they generate a sequence
> > of tones which is then processed by the very same transmitter in the
> > very same way. The maximum output bandwidth is supposed to be
somewhat
> > limited in the bandpass of the transmitter circuitry (which is NOT
> > being altered). Again, NO transmitter circuitry is being altered in
> > any way that I am aware of.
> >
> > With this discussion, how do we arbitrarily change the transmitter
> > output definitions? I am truly asking because that is a concept
beyond
> > my feeble mind. I really do not know. To me, regardless of the
> > "source" of the modulation itself, the modulation still remains an
> > offset of the carrier frequency by the frequency of the input tone.
> >
> > To me, the discussion of particular FCC designators for any of these
> > modes is rather moot, unless there is some method to tie the two
> > together. To simply start an argument about a particular FCC rule,
> > without showing the correlation to the subject is somewhat like
> > arguing the color of orange peels in an apple pie instruction sheet.
> > They simply don't necessarily relate. Both may have valid points
about
> > their own arguments, but the tow simply do not go together.
> >
> > Am I missing something besides a few marbles now? My head is spinning
> > from all these rules being bandied about, that may have no
application
> > here at all.
> >
> > John
> > KE5HAM
> >
> >
>
