[digitalradio] Re: Curious sound card modes question -
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 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
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, 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
Re: [digitalradio] Re: Curious sound card modes question -
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 -
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 -
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 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
Re: [digitalradio] Re: Curious sound card modes question -
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, KH6TY kh...@... wrote: John, Given sufficient carrier
Re: [digitalradio] Re: Curious sound card modes question -
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 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
[digitalradio] Re: Curious sound card modes question -
--- In digitalradio@yahoogroups.com, John ke5h...@... 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 -
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 mailto:digitalradio%40yahoogroups.com, John ke5h...@... 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 -
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
[digitalradio] Re: Curious sound card modes question -
Thanks I think you make the same point as I am seeking Just because the author of the program calls his great work spread spectrum does not necessarily make it so. Sorry Jose Here is partially why I ask for better clarification In Jose's documentation, one of his remarks seems to actually remove a qualifier of spread spectrum by his own statement as to why he did not do certain things. That is, in every spread spectrum system I have ever worked with (microwave, cordless phones, and numerous others), for the systems to work, each end had to be pre-programmed to a matching specific coded algorithm in order for the receivers and transmitters to hop frequencies in the exact same pattern and sync with each other. This pattern was pre-determined by that algorithm and NOT by ANY of the input data whatsoever. In other words, even if there were no input to the transmitter, it would still hop and transmit on it's pre-determined frequency pattern. The presence or absence of data at any given point in time would certainly affect the output of the transmitter at that particular instant, but would not affect the pre-determined frequency, but rather it's phase usually. NOW, with that said, this also would cause one other thing to happen, that has already been stated in the discussions. In true spread spectrum, if you were to look at the entire transmitted signal on an appropriate spectrum analyzer, you would see that the entire spectrum of the transmitted signal would be spread evenly throughout the bandwidth, regardless of input data. This is not necessarily true of an FSK / PSK signal in the short term. In the long term averaged over a period of time it may end up that way. Also of note, the frequency hopping characteristics of FSK/PSK modes are the result of the input data alone, not due to a pre-determined frequency pattern. Jose's documentation specifically mentioned NOT doing this for the reason of nobody would know what code to preset to be able to listen for CQ's, etc. Since Jose specifically chose not to implement this form of coding, to my way of thinking it also removes one of the specific defining points required to qualify as true spread spectrum. So the question remains is it really spread spectrum or not? Until that question is really answered, then any discussion of legality remains moot. Just because Jose declares it as spread spectrum does not make it that way. And unless a signal really is spread spectrum, then the well known laws against it's use on HF frequencies does not apply here. At the same time, if it does turn out that his definition IS correct and it IS spread spectrum rather than FSK or PSK (BPSK), then we now have numerous other common sound card based digital modes that become just as illegal because they operate the SSB transmitter in exactly the same way, by applying a variety of tones in different patterns to the audio input of it and them modulating it, which in turn causes the transmitter to output on a variety of different instantaneous frequencies based on that input data. The question of If we run RTTY with 850 Hz shift like we did in the old days, has that turned into spread spectrum? is a very valid question indeed ... John KE5HAM --- In digitalradio@yahoogroups.com, jhaynesatalumni jhhay...@... wrote: --- In digitalradio@yahoogroups.com, John ke5ham3@ 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?
