Re: [digitalradio] Re: OFDM Proposal
I don't know if this info is much use but Skysweep Technologies bundle an OFDM (TX RX) mode with their SkySweeper 5.12 package. http://www.skysweep.com/skysweep.html The mode is called SkyOFDM and from their help file: SkyOFDM is a state of art high speed modem based on the OFDM and turbo coding technologies. It offers several baud rates (300-9600 bps) and two different interleaving options (short and long). Also there are two bandwidth options: 2.0 and 2.6 kHz.The receiver should be set to the USB reception mode. The VHF/FM variant is not included in the SkySweeper Professional product. The high baud rates of SkyOFDM are very sensitive to signal clipping, so please set the transmitted signal level carefully. The peak to average ratio (crest factor) is up to 10 dB depending the baud rate. I haven't used it though. 73 Sholto KE7HPV. - Original Message - From: Rud Merriam [EMAIL PROTECTED] To: digitalradio@yahoogroups.com Sent: Sunday, October 21, 2007 10:13 PM Subject: RE: [digitalradio] Re: OFDM Proposal Ed, I am looking into the possibilities of OFDM. Right now I am stumbling over how to modulate the sub channels using the IFFT. g Actually, I think it is done by putting equal values in the real and imaginary parts of a bin and then doing the IFFT but need to try it out. I am a big proponent of FEC feeling it is woefully underused in ham digital modes. If you ain't FEC'n; you ain't tryin'. More pragmatically if you don't need FEC then you are using more bandwidth or power than necessary. One form of FEC I am curious about is putting FEC on each symbol. It has been an awfully long time that I looked at the error correcting codes (ECC) that are used in computer memory so I do not recall the details. A little research should remedy that memory failure. But putting 2 bit detection with 1 bit correction on a byte wide symbol might be worth the effort. In other words, stand by while I play with this. I will keep the group updated either by direct results or questions. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Ed Hekman Sent: Sunday, October 21, 2007 11:55 PM To: digitalradio@yahoogroups.com Subject: [digitalradio] Re: OFDM Proposal Rud, I would really enjoy hearing some discussion on the use of OFDM on HF. I work on an OFDM project and have an understanding of how it works although I am not a system designer. I have also tried OFDM with HamPal (digital SSTV) and WinDRM (digital voice) and it seems to me that it offers a lot of potential for improving performance with HF multipath fading. To stimulate some discussion I would like to ask some questions for the experts in the field.
[digitalradio] Re: OFDM Proposal
Could a higher higher success rate without the fill requests be achieved with some combination of better FEC, slower data rate, better spreading of the data over frequency and/or time? Try it. It's all there. FEC, data spreading and data rate can be selected in DRM, read the doc. Easypal has an additional FEC mode with much wider data spreading and another layer of high-efficiency FEC. By doubling the transmission time, you can recover up to 50% of the data ... Would it be feasible to use OFDM (or any other mode) with much longer ARQ cycle times (several seconds) to accomodate the computer timing limitations? This is already done. Find out how the bsr-stuff works. The limitation is that it's not automatic. This was an intentional design decision. We dont want a bunch of drm-robots on the qrg.
Re: [digitalradio] Modes the work with SSB splatter
When I am camping in the south of Spain through the winter, every sunday morning our 30m pskmail link to Sweden is covered up by splatter from french SSB stations. Pskmail makes use of the gaps in the conversation (there are weak and strong stations in the round) and delivers the information. The ARQ does this job by working around the qrm, not through it. 73, Rein PA0R -Ursprüngliche Nachricht- Von: digitalradio@yahoogroups.com Gesendet: 22.10.07 04:09:58 An: digitalradio@yahoogroups.com Betreff: [digitalradio] Modes the work with SSB splatter I was trying to work some 40 meter digital this evening but there are stations that have some audio extending down to 7070 which makes it difficult to use digital up at 1500 up from 7071. In fact, for a while PJ2/WK4Y was operating LSB right on 7071.5 which I think would put his passband right over the PSK31/digital mode waterhole. I was calling CQ in MFSK16 and Frank, K1CRU came back to me from CT. I was only able to copy a small percentage however he was able to copy me 100% because he did not have the interference. We tried switching to Olivia 500/16 but that was worse and copy was barely 10% on my end, but again, 100% on his. I then suggested we try Domino EX 8 which is available in Ham Radio Deluxe/Digital Master 780, but was not able to copy him after that. I would like to hear opinions on other's experiences working through voice splatter? I know that MT-63 can work except that the wider versions can not work as deep in the noise as you find with modes like MFSK16. What have you found that worked and what did not work. 73, Rick, KV9U -- http://pa0r.blogspirit.com Announce your digital presence via our Interactive Sked Page at http://www.obriensweb.com/drsked/drsked.php Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ * Your email settings: Individual Email | Traditional * To change settings online go to: http://groups.yahoo.com/group/digitalradio/join (Yahoo! ID required) * To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[digitalradio] Ignoring Other Modes and Languages Re:SSB splatter
Rein PA0R wrote When I am camping in the south of Spain through the winter, every sunday morning our our 30m pskmail link to Sweden is covered up by splatter from french SSB stations. Pskmail makes use of the gaps in the conversation Hi Rein, I am curious about the splatter. Normally, splatter refers to unusually high spurious signals that are emitted by an improperly adjusted SSB voice transmitter. The splatter is the spurious signal(s) adjacent to the main normal SSB voice signal channel, usually a result of poor linearity in the transmit amplifier chain. When one is not tuned to the transmitting SSB station's channel, their splatter normally shows up as a popping sound during voice peaks or sibilance excursions. Many of the FEC or ARQ digi modes can deal with low amplitude splatter. 2kHz bandwidth Olivia might be one of the more resilient modes for FEC work. Of course, almost any ARQ might work fine, such as PSK-ARQ. But, perhaps you are dealing more with a co-channel undesired SSB signal, or an overlapping channel SSB signal? If such is the case, then it isn't really splatter, is it? If the objective is to get a digital data signal through during a co-channel simultaneous SSB voice QSO, then one might wonder if QSY or QRX could be the preferred technique, rather than QRM-anti-QRM :) In any case, if a voice SSB station happens to be operating on one's favorite digi data channel, perhaps patience is the best mode of operation. But, sometimes there are situations when one must simply get the message through, and the interference is not mutual. Such is the problem on the 7MHz band, where stations in many parts of the world often operate between AM broadcast carriers, but within the AM audio sidebands. In USA, there is a very narrow automatic subband on 7MHz at 7100-7105kHz. It also happens to be adjacent to a strong AM broadcast station at 7105kHz, and it has a powerful audio Lower Sideband directly co-channel with the segment. Most of the hams successfully using this segment are using ARQ modes, but the communication still suffers or slows down, because the messaging and signalling often takes many repeats. I'm sure a lot of us have seen mini mode wars erupt spontaneously, especially on 7MHz, due to the disparate bandplans and allocations throughout the world. It isn't uncommon to see a CW station fire up on top of a digi texting QSO in the 7025-7045kHz area of the band, or vice-versa. We see a lot of digi texting ops in USA fire up directly on top of SSB QSOs in the 7060-7085kHz area. Often, these are situations where SSB QSOs with different languages are in progress. Perhaps it is in our nature for humans to ignore other languages that are not our own, and there is a parallel to this with ignoring other modes which we can't or don't want to take the time to decode. The 7MHz band in South America has been entirely taken over by unlicensed SSB voice stations mostly operating in USB. 7000kHz is like a continuous zoo, similar to the cacophony of the CB trucker channel on a big highway. In order for hams to have any effective use of the 7MHz band there, one must operate in country-wide nets and maintain large group QSOs on SSB, with the wagons circled in the area of 7070-7100kHz. 10MHz is a more difficult problem, because hams are secondary users of this shared band. How are hams to know which stations are the real primary users, and which ones are pirates? This is a huge problem on a number of ham bands in the tropical and equatorial areas of the world. Here in Asia, due to the vast number of languages and dialects one can hear on the air, it is almost impossible for the average ham to sort out whether they are hams or not, and whether one must yield to all of them. I'm sure it is similar for you in Spain, with its proximity and excellent propagation to Africa and all of Europe. Bonnie VR2/KQ6XA
Re: [digitalradio] Ignoring Other Modes and Language s Re:SSB splatter
Rein PA0R wrote When I am camping in the south of Spain through the winter, every sunday morning our our 30m pskmail link to Sweden is covered up by splatter from french SSB stations. Pskmail makes use of the gaps in the conversation Hi Rein, I am curious about the splatter. Normally, splatter refers to unusually high spurious signals that are emitted by an improperly adjusted SSB voice transmitter. The splatter is the spurious signal(s) adjacent to the main normal SSB voice signal channel, usually a result of poor linearity in the transmit amplifier chain. When one is not tuned to the transmitting SSB station's channel, their splatter normally shows up as a popping sound during voice peaks or sibilance excursions. Many of the FEC or ARQ digi modes can deal with low amplitude splatter. 2kHz bandwidth Olivia might be one of the more resilient modes for FEC work. Of course, almost any ARQ might work fine, such as PSK-ARQ. But, perhaps you are dealing more with a co-channel undesired SSB signal, or an overlapping channel SSB signal? If such is the case, then it isn't really splatter, is it? Hey Bonnie, I am referring to splatter. The SSB stations are 4 kHz down from our frequency, and some are seriously overdriving their amps. In Region 1, only french stations can work broadband on 30m, all other countries have a 500 Hz bandwidth limitation. They normally keep away from the top of the band, because of the 300 Bd packet APRS channel there. Also there, 20% of the stations are splattering (they work 10.151 MHz LSB to keep the audio harmonics inside the ham band). We have chosen our main frequency (10148.25) to be between their base band and their 2nd audio harmonic... because of the peculiar sound we call it the 'pregnant sea lion'. If the objective is to get a digital data signal through during a co-channel simultaneous SSB voice QSO, then one might wonder if QSY or QRX could be the preferred technique, rather than QRM-anti-QRM :) In any case, if a voice SSB station happens to be operating on one's favorite digi data channel, perhaps patience is the best mode of operation. But, sometimes there are situations when one must simply get the message through, and the interference is not mutual. Such is the problem on the 7MHz band, where stations in many parts of the world often operate between AM broadcast carriers, but within the AM audio sidebands. In USA, there is a very narrow automatic subband on 7MHz at 7100-7105kHz. It also happens to be adjacent to a strong AM broadcast station at 7105kHz, and it has a powerful audio Lower Sideband directly co-channel with the segment. Most of the hams successfully using this segment are using ARQ modes, but the communication still suffers or slows down, because the messaging and signalling often takes many repeats. I think mixing digital and phone operation is generally not a good idea, as the 'enemies' cannot understand each other. Peaceful coexistance needs inter-communication. We used CW as an international language for that in the past... I'm sure a lot of us have seen mini mode wars erupt spontaneously, especially on 7MHz, due to the disparate bandplans and allocations throughout the world. It isn't uncommon to see a CW station fire up on top of a digi texting QSO in the 7025-7045kHz area of the band, or vice-versa. We see a lot of digi texting ops in USA fire up directly on top of SSB QSOs in the 7060-7085kHz area. Often, these are situations where SSB QSOs with different languages are in progress. Perhaps it is in our nature for humans to ignore other languages that are not our own, and there is a parallel to this with ignoring other modes which we can't or don't want to take the time to decode. The 7MHz band in South America has been entirely taken over by unlicensed SSB voice stations mostly operating in USB. 7000kHz is like a continuous zoo, similar to the cacophony of the CB trucker channel on a big highway. In order for hams to have any effective use of the 7MHz band there, one must operate in country-wide nets and maintain large group QSOs on SSB, with the wagons circled in the area of 7070-7100kHz. In EU we normally don't use 7 MHz for pskmail because the band is completely 'full' most of the time, so we choose to keep a low profile there. 10MHz is a more difficult problem, because hams are secondary users of this shared band. How are hams to know which stations are the real primary users, and which ones are pirates? This is a huge problem on a number of ham bands in the tropical and equatorial areas of the world. Here in Asia, due to the vast number of languages and dialects one can hear on the air, it is almost impossible for the average ham to sort out whether they are hams or not, and whether one must yield to all of them. I'm sure it is similar for you in Spain, with its proximity and excellent propagation to Africa and all of Europe. The only
[digitalradio] QSO or QRM? ...or Contest?
The recent RTTY contest leads one to ponder: Why don't we see much backlash against contests? By orders of magnitude, contests create more QRM than any other cause on ham radio. They commonly render multiple ham bands nearly unusable for normal communications, for several days at a time. Yet, contesters creating maximum QRM are exalted as champions and Great Operators by the ham magazines and organizations. Why is a little QRM is bad, but vast and continuous QRM is wonderful? As quite an avid (and now reformed) contester myself, I'm very curious about this phenomena. 73 Bonnie VR2/KQ6XA
Re: [digitalradio] QSO or QRM? ...or Contest?
Bonnie , this is essentially a repeat of your point from several months ago. It is essentially trolling. I will close this topic. Andy K3UK On 10/22/07, expeditionradio [EMAIL PROTECTED] wrote: The recent RTTY contest leads one to ponder: Why don't we see much backlash against contests? By orders of magnitude, contests create more QRM than any other cause on ham radio. They commonly render multiple ham bands nearly unusable for normal communications, for several days at a time. Yet, contesters creating maximum QRM are exalted as champions and Great Operators by the ham magazines and organizations. Why is a little QRM is bad, but vast and continuous QRM is wonderful? As quite an avid (and now reformed) contester myself, I'm very curious about this phenomena. 73 Bonnie VR2/KQ6XA -- Andy K3UK www.obriensweb.com (QSL via N2RJ)
Re: [digitalradio] QSO or QRM? ...or Contest?
--- expeditionradio [EMAIL PROTECTED] wrote: The recent RTTY contest leads one to ponder: Why don't we see much backlash against contests? By orders of magnitude, contests create more QRM than any other cause on ham radio. They commonly render multiple ham bands nearly unusable for normal communications, for several days at a time. Bonnie I AGREE ! The problem is with contests they are not limited to a small part of any band so they TAKE OVER. They sit on known calling or net frequency's jamming them for hours or even DAYS at a time. AND are very quick to tell others that they HAVE EVERY RIGHT TO BE THERE. Its not limited to HF or any mode . On 50.125 MHz on 6 meters one of them Here in Florida will send CW for a while or until he feels he has run off the SSB users then switches to SSB to work the dx now that he has cleared the frequency off He does the same on 2 SSB. Bruce __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
Re: [digitalradio] QSO or QRM? ...or Contest?
Hi Bonnie, You are absolutely right. The only time i really have to do some DX is on weekends but nearly always I'm confronted with the whole bands occupied by contests. This weekend, there was a RTTY contest taking all the digi bands and at least one on SSB so all my DX interests (SSB and digi) were vanished by those contests. And like you said, there are a lot of complaints abt ALE reserving one frequency per band but contests are wiping all the freqs. Luc VE2FXL - Original Message - From: expeditionradio To: digitalradio@yahoogroups.com Sent: Monday, October 22, 2007 6:32 AM Subject: [digitalradio] QSO or QRM? ...or Contest? The recent RTTY contest leads one to ponder: Why don't we see much backlash against contests? By orders of magnitude, contests create more QRM than any other cause on ham radio. They commonly render multiple ham bands nearly unusable for normal communications, for several days at a time. Yet, contesters creating maximum QRM are exalted as champions and Great Operators by the ham magazines and organizations. Why is a little QRM is bad, but vast and continuous QRM is wonderful? As quite an avid (and now reformed) contester myself, I'm very curious about this phenomena. 73 Bonnie VR2/KQ6XA
Re: [digitalradio] Modes the work with SSB splatter
Who showed up first? I believe that on the light of the previous discussions, PJ2/WK4Y came first, he should not have been QRM'd with PSK, MFSK or whatever, and all activity should have stopped until that spectrum chunk was cleared, as SSB is authorized on those frequencies in this part of the world. So, PJ2/WK4Y was hidden to K1CRU but not to KV9U. PJ2/WK4Y should have not been willfully interfered, according to Part 97.101something... If the situation happened to be the contrary, someone should have plugged his microphone, fired up on LSB, and warned PJ2/WK4Y that the frequency was already in use in PSK, MFSK or Olivia. I am afraid that something does not fit...and not only with robots. A theory, in practice, may prove to be more complicated than the same theory, in theory. 73, Jose, CO2JA PS: Don't try to convince me of what is allowed and not, I know that the allowed modes do not match up in the States and down in the Caribbean. I am just taking adventage of the example posted. Life is certainly richer than we may imagine at a given moment. I am not looking forward to any further discussions or accusations. This is just food for thought. --- Rick wrote: I was trying to work some 40 meter digital this evening but there are stations that have some audio extending down to 7070 which makes it difficult to use digital up at 1500 up from 7071. In fact, for a while PJ2/WK4Y was operating LSB right on 7071.5 which I think would put his passband right over the PSK31/digital mode waterhole. I was calling CQ in MFSK16 and Frank, K1CRU came back to me from CT. I was only able to copy a small percentage however he was able to copy me 100% because he did not have the interference. We tried switching to Olivia 500/16 but that was worse and copy was barely 10% on my end, but again, 100% on his. I then suggested we try Domino EX 8 which is available in Ham Radio Deluxe/Digital Master 780, but was not able to copy him after that. I would like to hear opinions on other's experiences working through voice splatter? I know that MT-63 can work except that the wider versions can not work as deep in the noise as you find with modes like MFSK16. What have you found that worked and what did not work. 73, Rick, KV9U __ Participe en Universidad 2008. 11 al 15 de febrero del 2008. Palacio de las Convenciones, Ciudad de la Habana, Cuba http://www.universidad2008.cu
[digitalradio] Re: QSO or QRM? ...or Contest?
Luc, Guess what? Contesters work during the week too. Many have weekends only for radio. So you get them engaged in their favorite activity on weekends. Why is this hard to understand? They don't complain about the QRM but rather accept it as a challenge to overcome. I suspect this is also why CW/SSB and RTTY are preferred contest modes. There is a good chance for the human operator to make a difference and pull stations out of the QRM. They get really good at it too. You'll also find that these op's are quite technically savy and know propogation. Most of this is derived from years of station building and operating under highly variable radio conditions. Many of these guys run two radios simultaneously copying stations of one radio in the right ear and one in the left ear. Many can maintain rates of almost 200 QSO's/hour for hours at at time. This is why they are considered good operators. BTW: I'm not convinced the advanced digital modes allow for the operator to make any difference in copy-- at least not to the huge degree it is possible with analog modes. 30M, 17M, 12M are contest free zones. I can't answer the age old question why people engage in activites because they are hard but it is human nature. It is a heck of a lot easier to scale the 200' hill nearby than climbing Everest. Some choose Everest. A note of caution to those trying to develop the next digital killer ap. Be careful what you wish for. Assume you are successful and all hams switch over. You'll have the contest QRM environment to deal with. The will no little islands for protection left. 73 de Brian/K3KO Yet, contesters creating maximum QRM are exalted as champions and Great Operators by the ham magazines and organizations. Why is a little QRM is bad, but vast and continuous QRM is wonderful? As quite an avid (and now reformed) contester myself, I'm very curious about this phenomena. 73 Bonnie VR2/KQ6XA
Re: [digitalradio] Re: OFDM Proposal
Look at KA9Q's web site, especially http://www.ka9q.net/code/fec/, for FEC software. 73, John KD6OZH - Original Message - From: Rud Merriam To: digitalradio@yahoogroups.com Sent: Monday, October 22, 2007 05:13 UTC Subject: RE: [digitalradio] Re: OFDM Proposal Ed, I am looking into the possibilities of OFDM. Right now I am stumbling over how to modulate the sub channels using the IFFT. g Actually, I think it is done by putting equal values in the real and imaginary parts of a bin and then doing the IFFT but need to try it out. I am a big proponent of FEC feeling it is woefully underused in ham digital modes. If you ain't FEC'n; you ain't tryin'. More pragmatically if you don't need FEC then you are using more bandwidth or power than necessary. One form of FEC I am curious about is putting FEC on each symbol. It has been an awfully long time that I looked at the error correcting codes (ECC) that are used in computer memory so I do not recall the details. A little research should remedy that memory failure. But putting 2 bit detection with 1 bit correction on a byte wide symbol might be worth the effort. In other words, stand by while I play with this. I will keep the group updated either by direct results or questions. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Ed Hekman Sent: Sunday, October 21, 2007 11:55 PM To: digitalradio@yahoogroups.com Subject: [digitalradio] Re: OFDM Proposal Rud, I would really enjoy hearing some discussion on the use of OFDM on HF. I work on an OFDM project and have an understanding of how it works although I am not a system designer. I have also tried OFDM with HamPal (digital SSTV) and WinDRM (digital voice) and it seems to me that it offers a lot of potential for improving performance with HF multipath fading. To stimulate some discussion I would like to ask some questions for the experts in the field.
Re: [digitalradio] QSO or QRM? ...or Contest?
expeditionradio wrote: The recent RTTY contest leads one to ponder: Why don't we see much backlash against contests? More flame bait. de Roger W6VZV
Re: [digitalradio] Re: OFDM Proposal
OFDM is used by a number of programs as Ed mentions, but isn't this also the prime basis for many of our sound card modes? And Pactor 3? Most of the items mentioned below have been done or are currently used technology. One glaring exception is the lack of a narrow ARQ mode for keyboard that runs on the major platform. There is PSKmail on Linux but nothing for MS Windows, so this technology has not advanced very much. We do have wide ARQ mode now with FAE which uses the 8FSK signaling waveform from the older ALE designs. It is very wide and has mediocre performance by today's standards, but at least it is available now. Narrower and more robust waveforms would be welcome as a replacement. The timing issue with ARQ modems has not been a problem with moderately long transmissions of several seconds or more. Perhaps the main consideration is not the length of time for the transmission as much as the length of time of the window for the ACK/NAK. OFDM has trade-off issues since it spreads many tones simultaneously over a wide area. This leads to a crest factor that reduces power for any given tone compared to putting all the energy into one tone at a time. Because of the interpretation of the Part 97 rules, here in the U.S., we can use very wide band OFDM modes that have multiple carriers in the text digital areas of the bands, as long as none are faster than 300 baud. At the same time, we can not use high speed single tone modems when they exceed 300 baud and yet from what I have been able to determine, they are similar in bandwidth to OFDM. But we can use the high speed modems on the voice/image portions of the bands with what appears to be unlimited baud rates, and yet the proponents of these modems, never seem to be tested and reporting back to us how well they work. Instead they complain how we can not use them in the text digital portions of the bands. Can anyone explain this? 73, Rick, KV9U Ed Hekman wrote: Rud, I would really enjoy hearing some discussion on the use of OFDM on HF. I work on an OFDM project and have an understanding of how it works although I am not a system designer. I have also tried OFDM with HamPal (digital SSTV) and WinDRM (digital voice) and it seems to me that it offers a lot of potential for improving performance with HF multipath fading. To stimulate some discussion I would like to ask some questions for the experts in the field. The limitation that is often experienced with HamPal is that the probability of getting a complete file through without errors is small so it usually requires a manual request to fill in the holes. Looking at the waterfall display it is apparent that frequently there are transient holes in the spectrum due to multipath fading. Could a higher higher success rate without the fill requests be achieved with some combination of better FEC, slower data rate, better spreading of the data over frequency and/or time? There have been many discussions of the timing problems associated with using Pactor with computer sound cards. Would it be feasible to use OFDM (or any other mode) with much longer ARQ cycle times (several seconds) to accomodate the computer timing limitations? BPSK31 has become very popular due to its success with relatively low signal to noise ratios. I have noticed, though, that it does not perform well with the rapid flutter experienced with propagation over the pole even with good signal levels. Could this be be overcome with a little lower data rate (longer bit periods), better FEC, wider bandwidth, OFDM, etc? I have noticed that with signals coming over the North Pole, RTTY often works better than PSK31. Since RTTY (and MFSK, Olivia, etc.) only uses one tone at a time, it seems to me that OFDM which uses the entire bandwidth all of the time would be a more efficient use of the bandwidth. Is this reasonable? How do the various modes compare for efficiency of the bandwidth usage? I am familiar with Shannon's theorem but would like to know how OFDM compares to other modulation modes. There is quite a range of applications or uses of digital modes within the ham radio community. Each application has very different requirements. The applications range from: 1) Weak signal communications that require minimal information exchange and can take extended time periods (JT65, etc.). 2) Real time keyboard to keyboard QSOs with speeds ranging from a few words/minute to 50+ wpm. These uses can usually tolerate some errors. Narrow bandwidth also seems to be an advantage for these uses for a few different reasons. 3) Net operations. ARQ cannot be used since this is one to many communications. I have not participated in this type of operation so I am not familiar with how it is used or what is required. 4) File transfer or email - The highest possible data rate is preferred but the mode must be adaptable for varying
Re: [digitalradio] Modes the work with SSB splatter
Clearly, the 7070 watering hole is used 24/7 by narrow PSK31 stations as long as the band is open. The contester can unfortunately use SSB voice in that part of the band. He may not have known or cared that this is about the hottest digital area on 40 meters, but of course the PSK31 stations were there first. He may have been on earlier and the propagation could have changed. But probably not as he seemed to come out of nowhere and then got no response and gave up after a while. The other stations were higher in frequency and I could not be sure of the language. It sounded like French but perhaps a Caribbean patois? Because of the type of smearing modulation from SSB, I have come to the conclusion that bandwidth is not a good way to segregate signals. The mode really does need to be taken into consideration. 73, Rick, KV9U Jose A. Amador wrote: Who showed up first? I believe that on the light of the previous discussions, PJ2/WK4Y came first, he should not have been QRM'd with PSK, MFSK or whatever, and all activity should have stopped until that spectrum chunk was cleared, as SSB is authorized on those frequencies in this part of the world. So, PJ2/WK4Y was hidden to K1CRU but not to KV9U. PJ2/WK4Y should have not been willfully interfered, according to Part 97.101something... If the situation happened to be the contrary, someone should have plugged his microphone, fired up on LSB, and warned PJ2/WK4Y that the frequency was already in use in PSK, MFSK or Olivia. I am afraid that something does not fit...and not only with robots. A theory, in practice, may prove to be more complicated than the same theory, in theory. 73, Jose, CO2JA PS: Don't try to convince me of what is allowed and not, I know that the allowed modes do not match up in the States and down in the Caribbean. I am just taking adventage of the example posted. Life is certainly richer than we may imagine at a given moment. I am not looking forward to any further discussions or accusations. This is just food for thought.
Re: [digitalradio] Re: OFDM Proposal
The inputs to the FFT for each subcarrier are the sine and cosine of the phase of the signal. This is usually done in a lookup table. However, you're right that a FFT is inefficient for 9 subcarriers. Each could be generated by an accumulator and a sine/cosine lookup table. The input to the accumulator is the frequency of the subcarrier and the phase can be altered by adding to the output of the accumulator (modulo table size). Receiving would be done by multiplying the incoming signal by the sine and cosine of each subcarrier center frequency. The in-phase and quadrature outputs are then accumulated over the sample period. The phase change has to be done at the beginning of each sample period. This actually generates multiple sidebands as the modulating signal is a square wave. However, all sidebands except the first sideband cancel out if the subcarriers are evenly spaced. 73, John KD6OZH - Original Message - From: Rud Merriam To: digitalradio@yahoogroups.com Sent: Monday, October 22, 2007 15:40 UTC Subject: RE: [digitalradio] Re: OFDM Proposal Thanks, John, for this reference and the other responses. I do keep an eye on Phil's work and comments. Time for a direct question: How do you modulate an OFDM sub channel using an IFFT? Or is that not the way to do it in practice? I have experimented with Excel. Looking at the FFT of a cosine wave I get a nice solid single frequency bin. Doing a modulation of it with a phase change in the middle I get a number of bins which looks impractical to implement. A value in a single bin then running an IFFT generates a nice cosine. I can kind of make a PSK modulate signal by copying 3 values from the FFT experiment above but other attempts generate a mess. g Again, that does not seem like a feasible approach. Musing about it while going to sleep I got thinking about another approach based on the observation that the sign of a value in the complex number controls the phase of the start of the curve. The process is: Generate a symbol If a phase change is needed change the sign in the bin Generate the next symbol The trick is that the symbols are offset by 1/2 the timing period, i.e. the start of the 2nd symbol is actually the midpoint of the 2nd symbol. This works because in OFDM the symbol period contains complete cycles of the waves. Possibly using the IFFT for an HF OFDM signal is inefficient, especially when working with a 500 Hz bandwidth signal. The 62.5 baud suggestion you made only using 9 tones so generating them directly would not be a CPU intensive process, especially using table lookups. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of John B. Stephensen Sent: Monday, October 22, 2007 7:40 AM To: digitalradio@yahoogroups.com Subject: Re: [digitalradio] Re: OFDM Proposal Look at KA9Q's web site, especially http://www.ka9q.net/code/fec/, for FEC software. 73, John KD6OZH
[digitalradio] Re: Modes the work with SSB splatter
I want to point out that 7070 and the surrounds are part of the phone band in Europe and elsewhere(e.g. Canada). It has been that way long before any of these digital modes existed. It isn't just contests. It is a very popular spot day in and day out. The BC stations in EU from 7100 up make that part of their phone allocation impossible to use. It might be argued by the SSB guys that the digital mode doesn't belong there. 40 M allocations have been screwed up since forever due to broadcast interests and ham radio interests colliding. 73 de Brian/K3KO -- In digitalradio@yahoogroups.com, Rick [EMAIL PROTECTED] wrote: Clearly, the 7070 watering hole is used 24/7 by narrow PSK31 stations as long as the band is open. The contester can unfortunately use SSB voice in that part of the band. He may not have known or cared that this is about the hottest digital area on 40 meters, but of course the PSK31 stations were there first. He may have been on earlier and the propagation could have changed. But probably not as he seemed to come out of nowhere and then got no response and gave up after a while. The other stations were higher in frequency and I could not be sure of the language. It sounded like French but perhaps a Caribbean patois? Because of the type of smearing modulation from SSB, I have come to the conclusion that bandwidth is not a good way to segregate signals. The mode really does need to be taken into consideration. 73, Rick, KV9U Jose A. Amador wrote: Who showed up first? I believe that on the light of the previous discussions, PJ2/WK4Y came first, he should not have been QRM'd with PSK, MFSK or whatever, and all activity should have stopped until that spectrum chunk was cleared, as SSB is authorized on those frequencies in this part of the world. So, PJ2/WK4Y was hidden to K1CRU but not to KV9U. PJ2/WK4Y should have not been willfully interfered, according to Part 97.101something... If the situation happened to be the contrary, someone should have plugged his microphone, fired up on LSB, and warned PJ2/WK4Y that the frequency was already in use in PSK, MFSK or Olivia. I am afraid that something does not fit...and not only with robots. A theory, in practice, may prove to be more complicated than the same theory, in theory. 73, Jose, CO2JA PS: Don't try to convince me of what is allowed and not, I know that the allowed modes do not match up in the States and down in the Caribbean. I am just taking adventage of the example posted. Life is certainly richer than we may imagine at a given moment. I am not looking forward to any further discussions or accusations. This is just food for thought.
[digitalradio] 30m Slowfeld beacon QRT
Hi all, Thank you all for your reports. The response has been overwhelming. Special thanks to those of you that have had the grabber's going on the net. It has been amazing to see my low power signal crawling over the screens. The beacon will be off for a while, but it will be back. Maybe in another weak signal mode. I am reading about WOLF now , it seems really interesting. 73 de LA5VNA Steinar
