Re: [digitalradio] Re: Curious sound card modes question -

[J. Moen]

Skip KH6TY wrote: "In fact actress Hedy Lamarr invented spread spectrum, and 
you can read that here: http://en.wikipedia.org/wiki/Hedy_Lamarr.";

While frequency-hopping was first introduced in a patent filed by Nikola Tesla 
in 1900, I've always been fascinated by the role of Austrian actress Hedy 
Lamarr in the development of spread-spectrum.  

According to Wikipedia,  (following is quoted from their site): Avant garde 
composer George Antheil, a son of German immigrants and neighbor of Lamarr, had 
experimented with automated control of musical instruments, including his music 
for Ballet Mecanique, originally written for Fernand Léger's 1924 abstract 
film. This score involved multiple player pianos playing simultaneously.

Lamarr had learned about the problem at defense meetings she had attended with 
her former husband Friedrich Mandl, who was an Austrian arms manufacturer. 

Together, Antheil and Lamarr submitted the idea of a secret communication 
system in June 1941. On August 11, 1942, U.S. Patent 2,292,387 was granted to 
Antheil and "Hedy Kiesler Markey", Lamarr's married name at the time. This 
early version of frequency hopping used a piano roll to change between 88 
frequencies and was intended to make radio-guided torpedoes harder for enemies 
to detect or jam.

The patent came to light during patent searches in the 1950s when ITT 
Corporation and other private firms began to develop Code Division Multiple 
Access (CDMA), a civilian form of spread spectrum.

  Jim - K6JM

  - Original Message - 
  From: KH6TY 
  To: digitalradio@yahoogroups.com 
  Sent: Monday, February 22, 2010 5:30 PM
  Subject: Re: [digitalradio] Re: Curious sound card modes question -  
  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

Re: [digitalradio] Re: Curious sound card modes question -

[mikea]

On Mon, Feb 22, 2010 at 08:30:29PM -0500, KH6TY wrote:
> 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.

She invented FHSS as a torpedo control technique; most folks don't know
that she had an EE degree. DSSS came about later, as a classified technique
called "Phantom", to permit transmissions with a low probability of
interception ("LPI"). With a typical 3 KHz bandwidth receiver, or even a 50
KHz wide panadaptor, you won't see all the spectrum from a wideband (say,
100 KHz spreading code) DSSS transmission. You may notice only a slightly
raised noise floor.

But that's only part of the deal with DSSS. The correlation and despreading
produces a really nice gain in noise immunity, as well.

-- 
Mike Andrews, W5EGO
mi...@mikea.ath.cx
Tired old sysadmin 

Re: [digitalradio] Re: Curious sound card modes question -

[KH6TY]

No, the shift on RTTY and other soundcard modes is not determined by a 
pseudo random code but always known and predictable. Instead, the tones 
on ROS are driven by a code signal. To quote from the ROS documentation, 
"2. Spreading is accomplished by means of a spreading signal, often 
called a code signal, which is independent of the data."


The original intent of spread spectrum was to make it impossible to 
monitor without possessing the despreading code, but ROS can be monitored.


There is a good chance that the FCC will allow us to use ROS on HF - why 
not! But as the rules are written right now, ROS is FHSS - by design, 
and it does not matter if the description is changed or not, so it is 
necessary to get a waiver or other FCC agreement that we can use it on 
HF. ROS can be copied by third parties, and is no wider than a phone 
signal, so I cannot think of any reason the FCC would decline, but they 
have to give permission. That is just the way it works, because that is 
how the rules happen to have been written in the past.


If  the spreading is NOT actually "accomplished by means of a spreading 
signal, often called a code signal, which is independent of the data" 
then ROS is not spread spectrum and there is no problem.


73 - Skip KH6TY




jhaynesatalumni wrote:
 




--- In digitalradio@yahoogroups.com 
, "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.

>

That's a good question. If we run RTTY with 850 Hz shift like we
did in the old days, has that turned into spread spectrum?

Re: [digitalradio] Re: Curious sound card modes question -

[Alan Barrow]

KH6TY wrote:
> 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.
>

The key is the "much in excess"  in  item 1.  If you were to use 31hz vs
2000, you'd be approaching the minimum bandwidth expansion factor in
practical usage at 64:1. I'd have to go look at realistic bandwidth for
psk, I was thinking it's a bit higher in the real world. Modern SS runs
way higher, often 1000:1.

But just like the fsk symbol rate anachronism in the regs, I suspect the
spread spectrum restriction in the regs was targeted the very broad
(50-100khz minimum) spread spectrum signals. Realistically, they did not
anticipate that we'd have the capability to do SS in a 2khz signal. (and
we probably could not have pre-sound card)

But after reading the NTIA definition, and the one in the docs, I agree
it's technically SS by a strict interpretation. Just like P3 is
technically FDM. But since both live in a SSB signal bandwidth, they are
not what the regs were trying to prevent.

Based on the FCC ruling on P3 OFDM, my suspicion is they'd fall in favor
of ROS. I don't see a practical reason for them to disallow it, it does
not have expanded footprint, etc.

But all this points out to me how out of date the US regs are! It would
be easier if they had used the NTIA definition, and ideally put some
practical measures around bandwidth expansion factor and overall bandwidth.

No matter what, it's a neat idea, and thanks for taking the time to code it!

have fun,

Alan
km4ba

Re: [digitalradio] Re: Curious sound card modes question -

[KH6TY]

Gentlemen,

I have spent way too much time with my limited knowledge trying to make 
some sense of this issue and answer questions. I am going to use ROS on 
UHF only anyway, and it is legal there no matter if it is FHSS or not, 
so I'll leave it to the rest of you to discuss the issue.


Thanks for the bandwidth and I hope it can be used on HF!

73, Skip, KH6TY

Re: [digitalradio] Re: Curious sound card modes question -

[KH6TY]

That is only ONE of the three conditions outlined by Jose. I thought I 
did not need to repeat the other two.


73 - Skip KH6TY




Dave AA6YQ wrote:
 

re "PSK31 accomplishes the same typing speed in a bandwidth of 31 Hz, 
instead of in 2000 Hz, so ROS is probably truly spread-spectrum."
 
Applying this logic to RTTY, which employs ~10X the bandwidth employed 
by PSK31, would lead us to conclude that RTTY is also spread spectrum.
 
73,
 
Dave, AA6YQ
 
-Original Message-
*From:* digitalradio@yahoogroups.com 
[mailto:digitalra...@yahoogroups.com]*on Behalf Of *KH6TY

*Sent:* Monday, February 22, 2010 8:30 PM
*To:* digitalradio@yahoogroups.com
*Subject:* Re: [digitalradio] Re: Curious sound card modes question -

 

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

RE: [digitalradio] Re: Curious sound card modes question -

[Dave AA6YQ]

re "PSK31 accomplishes the same typing speed in a bandwidth of 31 Hz,
instead of in 2000 Hz, so ROS is probably truly spread-spectrum."

Applying this logic to RTTY, which employs ~10X the bandwidth employed by
PSK31, would lead us to conclude that RTTY is also spread spectrum.

73,

Dave, AA6YQ

-Original Message-
From: digitalradio@yahoogroups.com [mailto:digitalra...@yahoogroups.com]on
Behalf Of KH6TY
Sent: Monday, February 22, 2010 8:30 PM
To: digitalradio@yahoogroups.com
Subject: Re: [digitalradio] Re: Curious sound card modes question -



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, KH6TY  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

Re: [digitalradio] Re: Curious sound card modes question -

[KH6TY]

The only entity competent to answer the question is the FCC, and the 
accepted procedure when one is not sure is to ask for a clarification. 
Unfortunately, it is everyone's legal responsibility to understand the 
law and obey it. Since most of use cannot do that, we have to turn to 
lawyers to do it. You may or may not like the answer given, but the FCC 
does try to protect the ham bands for everyone and seems to make 
interpretations on that basis. Digital users are a tiny minority of 
users of the bands, but the FCC is accountable to all hams, so they must 
try to do what is right for all hams, not just for a minority. If it 
were not for that approach, the HF bands today might be covered with 
automatic messaging systems and it would be hard to even find a place to 
play or have a QSO without interference from an automatic station that 
does not listen first, does not QRL, and does not share frequencies. We 
may not like the time it takes for the process to play out, but that 
gives everyone a chance to present their case before any rules are made 
- EVERYONE, not just a vocal minority.


73 - Skip KH6TY




Alan Barrow wrote:
 


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.

>

OFDM used in Pactor 3 is legal due to it's low symbol rates and SSB
sized effective bandwidth. If prior to P3 someone asked if FDM was legal
on HF most would say no. Traditional FDM (frequency division
multiplexing) as practiced in the real world would not ever be legal on
HF. So technically it's FDM, but practically, it's not, as it's much
narrower bandwidth.

Lumping ROS in with Spread spectrum is similar. You can use FDM or SS
approaches on an audio modulated sideband signal and not meet practical
definitions. quack test- walks like a duck, must be a duck.

Regarding the perfect SSB transmitter sending a 1khz tone equaling CW at
a 1khz beat frequency, we all know there is a big difference between
theoretical and reality.

But in theory, ROS, P3, whatever could be represented by multiple
transmitter signals, so could technically fall into legal gray area. I'm
sure if we tried hard enough we could find a way to decide it's illegal,
and should be banned. And in reality, the FCC won't care, as it did not
meet the quack test of spread spectrum. :-)

I don't have a horse in this race, however. :-)

Have fun,

Alan
KM4BA

Re: [digitalradio] Re: Curious sound card modes question -

[Alan Barrow]

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.
>   

OFDM used in Pactor 3 is legal due to it's low symbol rates and SSB
sized effective bandwidth. If prior to P3 someone asked if FDM was legal
on HF most would say no. Traditional FDM (frequency division
multiplexing) as practiced in the real world would not ever be legal on
HF. So technically it's FDM, but practically, it's not, as it's much
narrower bandwidth. 

Lumping ROS in with Spread spectrum is similar. You can use FDM or SS
approaches on an audio modulated sideband signal and not meet practical
definitions. quack test- walks like a duck, must be a duck.

Regarding the perfect SSB transmitter sending a 1khz tone equaling CW at
a 1khz beat frequency, we all know there is a big difference between
theoretical and reality.

But in theory, ROS, P3, whatever could be represented by multiple
transmitter signals, so could technically fall into legal gray area. I'm
sure if we tried hard enough we could find a way to decide it's illegal,
and should be banned. And in reality, the FCC won't care, as it did not
meet the quack test of spread spectrum. :-)

I don't have a horse in this race, however. :-)

Have fun,

Alan
KM4BA

Re: [digitalradio] Re: Curious sound card modes question -

[KH6TY]

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 
, KH6TY  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 sourc