Re: [digitalradio] Re: Digital Voice: Some thoughts after one week.
I think in addition to one table per language you will also need different tables for 75m than for 20m., hihi. Leigh/WA5ZNU On Fri, 13 Oct 2006 1:15 am, Rein Couperus wrote: > I a working on such a scheme for PSKmail, with tables of 32k standard > words (1 for each language), Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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/
RE: [digitalradio] Re: Digital Voice: Some thoughts after one week.
Rick et. al., The commercial HF folks already have higher throughput data modes...close to 9600 bps user throughput (now RAW throughput) but the signal is 6-8 KHz wide and they give this throughput at 0 to -5 dB SNRs. Thus far DV hasn't made such progress but Thompson CSF and their New Generation HF Modem (http://www.argreenhouse.com/society/TacCom/papers98/11_04i.pdf#search=%22NEW%20STUDIES%20ABOUT%20A%20HIGH%20DATA%20RATE%20HF%20PARALLEL%20MODEM%22)may improve data and DV capability.* I would assume that Thales is looking at Thompson's work. * User Available Data Rate Modulation and Coding Symbol Rate 9600 bpsTurbo Code QAM 64 3/4 2133 baud 4800 bpsTurbo Code QAM 16 3/5 2000 baud 2400 bpsTurbo Code QPSK 3/5 2000 baud There is a great difference in real time voice and data but what is the definition of real time voice? Can we wait 5-10 seconds between the time the sender stops and we start receiving? We can't even wait for the curtsey tone on repeaters...how can we wait for a DV epoch to demodulate? When I speak of an HF signal, I always assume a poor CCIR signal with much fading, etc. The best HF SSB signal is still a poor POTS signal. Things to do...push until we start seeing the Shannon Limit. Start "training" our transmissions/packets/data. Define/determine the best receive filter(s). Determine which modulation technique is best (this research may have already been done.) Push bandwidth. test and retest the signal coding and interleaving. Determine the balance between the amount of FEC to be used vs. ARQ. Determine if broadcast and messages modes are needed and if different are needed, what parts of the code are reusable/common. The same for DV. Can we reuse the code for V/UHF communications? Define a standard test simulation model, i.e. the KC7WW channel simulator or Moe Wheatly's channel simulator. Set a standard test text and test binary. I believe that when we get DV with the quality as good or better than the current AOR DV and operating at a 0 or less SNR, we will replace current analog SSB. I also believe that this will not be done until we start seeing more SDR hardware on the market. I have but a little time left to see all this come to true...I hope I do get to see it. 73, Walt/K5YFW -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] Sent: Wednesday, October 11, 2006 3:54 PM To: digitalradio@yahoogroups.com Subject: Re: [digitalradio] Re: Digital Voice: Some thoughts after one week. The one common theme I see with much of the digital modes that require the higher level of speed is that the required minimum S/N ratio hovers around 10 db S/N. It seems to be true with DV voice, with SCAMP, and also with high baud rate modes (such as trying to exceed a few hundred baud on HF). To me there is a dividing line between real time voice and high speed digital texting vs. slower modes that get through under difficult conditions. Actually, difficult conditions tend to be more of the norm on HF. Does anyone have any "inside" information that would suggest that we will be able to lower the required S/N ratios for a given speed or are we already too close to the Shannon Limit as it is? If we can not do this, I don't see how any of the higher speed digital modes will ever be able to replace analog communications for weak signal and general amateur radio communications with modest power levels and modest antennas. In other words, what most of us do most of the time. Of course this would not be true for VHF and up, only for the restricted BW's of HF. 73, Rick, KV9U DuBose Walt Civ AETC CONS/LGCA wrote: >Ed, > >Back in the fall of 1989, we started using a unit called the TacTerm for DV. >The best modem was a 39 parallel tone modem (Mil-Std-188-110?) and 2400 BPS. >On HF it sounded funny...robotic like...and while it did work on about the >same SNR as a ~S3 SSB signal ...the SNR had to be about 10 dB, it worked much >better on VHF and UHF FM as well as UHF AM. > >In Jan-Feb 1990, after Operation Just Cause, I got to play with a Harris >Mil-Std-188-110? modem and DV at 2400 BPS AND 4800 BPS. The 2400 bps DV still >sounded a bit robotic but worked quite well at S2-S3 signals and even when the >SNR was at or I think slightly below 10 dB. The modem had ALE and provided a >SNR figure and my old ham radio ear figured an S2-3 signal. > >When we switched to 4800 bps, the DV sounded just like the individual speaking >over a telephone...better than SSB voice but it required a slightly better SNR. > >Data with the TacTerm 39 tone modem was really good...text came through at >about a page a minute with a signal that you could hear. When the signal got >down close to the noise...where you had to strain to
RE: [digitalradio] Re: Digital Voice: Some thoughts after one week.
Hi Ed. I'm rarely on in the evenings and mainly on Saturday and Sunday afternoons and on holidays...and on rare occasions as K5STB/P on Saturdays. UR Questions... 1) Can you suggest a reference on HF propagation that may show distributions or histograms of fade depths, durations and bandwidths? No...I generally use the NVIS HAP charts from http://www.ips.gov.au/HF_Systems/7/1/1 Realtime fade depths, durations and bandwidths are going to change so much that you would probably have to be on-the-air at both ends of a path to determine this for any one band of frequencies. 2) For the examples of military equipment you gave, did they use voice bandwidths (~2.5 KHz) or were the bandwidths larger? Most has 2.7 KHz receiver bandpass filters or slighly less. CW filters were 400 Hz and AM filters were 6.x KHz. Most units used AME-USB with re-injected carrier so wht bandwidth was the same as SSB 3) With military communications I expect that voice quality and accuracy of the communication is essential. For ham weak signal applications where accuracy is not a life and death matter, can we gain any performance by trading codec data for FEC data? If voice quality at 2400 bps is considered acceptable for military applications, can we get better SNR performance with useable voice quality for ham applications at codec data rates less than 2400 bps with stronger FEC? You would think that voice quality and accuracy would be essential and in fact it is. However, the reason they sent from 1200 baud to 2400 baud for DV was just that and when signal levels were good enough, they used 4800 BPS. The robustness for the 2400 bps DV wasn't all that good...something more than a + 10 dB SNR was required. A more robust DV that would work with SNRs of 0 to -5 dB would be great...but then you could use 4800 bps DV at +10 SNRs. The qualitity of the AOR DV units is nice...very clear...I don't think that part needs much imporvement. However, they require such a high SNR that they can't be considered very robust. Walt/K5YFW -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] Sent: Wednesday, October 11, 2006 3:34 PM To: digitalradio@yahoogroups.com Subject: [digitalradio] Re: Digital Voice: Some thoughts after one week. --- In digitalradio@yahoogroups.com, "DuBose Walt Civ AETC CONS/LGCA" <[EMAIL PROTECTED]> wrote: > > I've heard DV using LCP-10 and a 16 tone modem as well as a 39 tone modem at 1200 bps...it sounds robotic at best. But that could have been just the systems used (ANDVT/Mil-STD-188-110) > > Walt/K5YFW Walt, Thanks for your very interesting and informative comments. I would be very interested in meeting you on the air for an extended conversation on the subject. We should be able to connect on 40M or 80M in the evenings. I often monitor 7295 +/-. I can also be reached on EchoLink. Some of the questions I have are: 1) Can you suggest a reference on HF propagation that may show distributions or histograms of fade depths, durations and bandwidths? 2) For the examples of military equipment you gave, did they use voice bandwidths (~2.5 KHz) or were the bandwidths larger? 3) With military communications I expect that voice quality and accuracy of the communication is essential. For ham weak signal applications where accuracy is not a life and death matter, can we gain any performance by trading codec data for FEC data? If voice quality at 2400 bps is considered acceptable for military applications, can we get better SNR performance with useable voice quality for ham applications at codec data rates less than 2400 bps with stronger FEC? Is there anyone reading this thread that could develop additional experimental modes for WinDRM? Ed WB6YTE Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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/
Re: [digitalradio] Re: Digital Voice: Some thoughts after one week.
Oops, I forgot about that 400 ms time segment! Yes, now I see what you mean. Thanks for helping clarify this. 73, Rick, KV9U cesco12342000 wrote: >>From my understanding of the documentation for WinDRM, MELP >>does work if the speed is at least 1,000 bps. >> >> > >No. 1000 bp400ms (bit per 400 ms) or 2400 bps >This per second / per 400 millisecond mixture is confusing ! > > > > > > >Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org > >Other areas of interest: > >The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ >DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) > > >Yahoo! Groups Links > > > > > > > > Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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] Re: Digital Voice: Some thoughts after one week.
> From my understanding of the documentation for WinDRM, MELP > does work if the speed is at least 1,000 bps. No. 1000 bp400ms (bit per 400 ms) or 2400 bps This per second / per 400 millisecond mixture is confusing ! Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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] Re: Digital Voice: Some thoughts after one week.
--- In digitalradio@yahoogroups.com, "Patrick Lindecker" <[EMAIL PROTECTED]> wrote: > I have listened some test in spanish with artificial voice reading words. It was not too bad. The real problem is to translate voice in symbols, in a reliable way. > Yes. There was that fairly recent QST article about using voice recognition software to operate PSK or other keyboard modes by voice. I copied a guy using it - it did fairly well, but of course had trouble with homonyms: e.g. "to" and "two" and "too" Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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/
Re: [digitalradio] Re: Digital Voice: Some thoughts after one week.
Glad that I was understanding that the 4-QAM was for the text part and not voice. At least at this point of technology advancement. Also, you had said earlier that: "Tests with a 1200 bit/sec LPC codec have been negative (bad intellegibility)." From my understanding of the documentation for WinDRM, MELP (which is really a form of LPC) does work if the speed is at least 1,000 bps. So what LPC codec is it that does not work at 1,200 bps? 73, Rick, KV9U cesco12342000 wrote: > See the list on the windrm spec page. > >http://www.qslnet.de/member/hb9tlk/drm_h.html > > > >>If LPC doesn't work at 1200 bps, >> >>And apparently it works OK at 1000 bps? >> >> > >I dont understand. > > > > > > >Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org > >Other areas of interest: > >The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ >DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) > > >Yahoo! Groups Links > > > > > > > > Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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/
Re: [digitalradio] Re: Digital Voice: Some thoughts after one week.
Hi Patrick and group, I wonder if there would be much interest in this kind of DV? The main argument was for having a high quality sounding voice in real time. In the early 1980's, there used to be a product called HERO (Heath Educational Robot) which allowed simple phoneme entry so that it could "speak." Of course it did a lot more with a robot arm and was ambulatory and had various sensors and sonar ranging, etc. I built one of these kits for a shared robot experience with our school districts and used to demonstrate it to teachers. The programming could be entered manually via a keypad. The voice quality not always easy to understand, and it was definitely what we call robotic:) If the phoneme quality was improved with a clearer sound that I am sure can be done with today's technology, I can see where a phoneme based system could theoretically work. I am not sure if it would receive wide adoption, but if it was the only way to effect weak signal voice, maybe it could have a niche area of interest? I wonder what other group members think about that? 73, Rick, KV9U Patrick Lindecker wrote: >Hello Rick, > > > >The only solution to do voice exchange with a low S/N would be to translate >all the pronounced words in symbols (through some program able to "understand" >voice, the symbols being phonemes or words), to code these symbols through a >Varicode with, for example 40.000 different symbols, to transmit these symbols >and to reverse the process at reception: decoding of the symbols and >pronunciation through an auxiliary program handling an artificial voice. >The transmission mode would be some MFSK16 or Contestia mode (rapid and >reliable). > >I have listened some test in spanish with artificial voice reading words. It >was not too bad. The real problem is to translate voice in symbols, in a >reliable way. > >I think that, in this way, the compression of the information would be close >to the maximum. > >73 >Patrick > > > Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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] Re: Digital Voice: Some thoughts after one week.
> The only solution to do voice exchange with a low S/N would > be to translate all the pronounced words in symbols Exactly what i am thinking! We need to establish a "phoneme alphabet". Then, a correlator is needed to extract those phonems from the voice input. Each phonem should have duration and pitch indicators to allow a more individual reconstruction of the voice. This would result in a robust, low-bitrate and somewhat robotic DV system. Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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] Re: Digital Voice: Some thoughts after one week.
> It was my understanding that the QAM-4 modulation was used for the > text transmission Negative. Text and data can be anything from qam-4 to qam-64 FAC data (the callsign) is the only thing which is always qam-4 > and you needed to use at least QAM-16 for the > voice. Since the codecs used have 2400bps data rate, qam-16 is necessary. But if you find a decent 1200bps codec, data rate is lower, and qam-4 could be enough. > How many bps can you get through with QAM-4? See the list on the windrm spec page. http://www.qslnet.de/member/hb9tlk/drm_h.html > If LPC doesn't work at 1200 bps, > > And apparently it works OK at 1000 bps? I dont understand. Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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/
Re: [digitalradio] Re: Digital Voice: Some thoughts after one week.
Hello Rick, >Does anyone have any "inside" information that would suggest that we >will be able to lower the required S/N ratios for a given speed or are >we already too close to the Shannon Limit as it is? The only solution to do voice exchange with a low S/N would be to translate all the pronounced words in symbols (through some program able to "understand" voice, the symbols being phonemes or words), to code these symbols through a Varicode with, for example 40.000 different symbols, to transmit these symbols and to reverse the process at reception: decoding of the symbols and pronunciation through an auxiliary program handling an artificial voice. The transmission mode would be some MFSK16 or Contestia mode (rapid and reliable). I have listened some test in spanish with artificial voice reading words. It was not too bad. The real problem is to translate voice in symbols, in a reliable way. I think that, in this way, the compression of the information would be close to the maximum. 73 Patrick - Original Message - From: KV9U To: digitalradio@yahoogroups.com Sent: Wednesday, October 11, 2006 10:54 PM Subject: Re: [digitalradio] Re: Digital Voice: Some thoughts after one week. The one common theme I see with much of the digital modes that require the higher level of speed is that the required minimum S/N ratio hovers around 10 db S/N. It seems to be true with DV voice, with SCAMP, and also with high baud rate modes (such as trying to exceed a few hundred baud on HF).To me there is a dividing line between real time voice and high speed digital texting vs. slower modes that get through under difficult conditions. Actually, difficult conditions tend to be more of the norm on HF.Does anyone have any "inside" information that would suggest that we will be able to lower the required S/N ratios for a given speed or are we already too close to the Shannon Limit as it is?If we can not do this, I don't see how any of the higher speed digital modes will ever be able to replace analog communications for weak signal and general amateur radio communications with modest power levels and modest antennas. In other words, what most of us do most of the time.Of course this would not be true for VHF and up, only for the restricted BW's of HF.73,Rick, KV9UDuBose Walt Civ AETC CONS/LGCA wrote:>Ed,>>Back in the fall of 1989, we started using a unit called the TacTerm for DV. The best modem was a 39 parallel tone modem (Mil-Std-188-110?) and 2400 BPS. On HF it sounded funny...robotic like...and while it did work on about the same SNR as a ~S3 SSB signal ...the SNR had to be about 10 dB, it worked much better on VHF and UHF FM as well as UHF AM.>>In Jan-Feb 1990, after Operation Just Cause, I got to play with a Harris Mil-Std-188-110? modem and DV at 2400 BPS AND 4800 BPS. The 2400 bps DV still sounded a bit robotic but worked quite well at S2-S3 signals and even when the SNR was at or I think slightly below 10 dB. The modem had ALE and provided a SNR figure and my old ham radio ear figured an S2-3 signal.>>When we switched to 4800 bps, the DV sounded just like the individual speaking over a telephone...better than SSB voice but it required a slightly better SNR.>>Data with the TacTerm 39 tone modem was really good...text came through at about a page a minute with a signal that you could hear. When the signal got down close to the noise...where you had to strain to hear it, the throughput went down to maybe 20-30 lines per minutebut still near 100% copy (could have been typing errors). The actual computer software was KA9Q NOS running on a BIG military laptop computer.>>When we went to the Harris modem and 2400 BPS/4800 BPS, the copy at 2400 BPS was about the same with a good signal but better than the TacTerm with lower qualitity signals.>>4800 bps screemed unless the signal got below 10 dB SNR or so.>>During Operations Desert Shield and Desert Storm, the U.S. Marine Corp used a Hughes RT-1209 and Harris AM-6545A 400 watt amplifier to make up the GRC-193A (http://www.nj7p.org/millist/pic/grc-193.gif) used in some of the last productions Jeeps and Humvees. Most were using a 15-16 ft fold over whip. The whip went up just about 18" higher then the Humvee top and then tilted over and ran horizontal the remainder of the length. This provided a good NVIS antenna radiation pattern.>>The Marine Corp did connect the Harris MIL-STD-188-110x modem to the GRC-193 and used a computer to send data from the field back to their command center.>>For digital voice I believe that some units used the Navy's version of the TacTerm and some may have been using the later ITT MinTerm DV unit. The TacTerm (KY-57) can
Re: [digitalradio] Re: Digital Voice: Some thoughts after one week.
The one common theme I see with much of the digital modes that require the higher level of speed is that the required minimum S/N ratio hovers around 10 db S/N. It seems to be true with DV voice, with SCAMP, and also with high baud rate modes (such as trying to exceed a few hundred baud on HF). To me there is a dividing line between real time voice and high speed digital texting vs. slower modes that get through under difficult conditions. Actually, difficult conditions tend to be more of the norm on HF. Does anyone have any "inside" information that would suggest that we will be able to lower the required S/N ratios for a given speed or are we already too close to the Shannon Limit as it is? If we can not do this, I don't see how any of the higher speed digital modes will ever be able to replace analog communications for weak signal and general amateur radio communications with modest power levels and modest antennas. In other words, what most of us do most of the time. Of course this would not be true for VHF and up, only for the restricted BW's of HF. 73, Rick, KV9U DuBose Walt Civ AETC CONS/LGCA wrote: >Ed, > >Back in the fall of 1989, we started using a unit called the TacTerm for DV. >The best modem was a 39 parallel tone modem (Mil-Std-188-110?) and 2400 BPS. >On HF it sounded funny...robotic like...and while it did work on about the >same SNR as a ~S3 SSB signal ...the SNR had to be about 10 dB, it worked much >better on VHF and UHF FM as well as UHF AM. > >In Jan-Feb 1990, after Operation Just Cause, I got to play with a Harris >Mil-Std-188-110? modem and DV at 2400 BPS AND 4800 BPS. The 2400 bps DV still >sounded a bit robotic but worked quite well at S2-S3 signals and even when the >SNR was at or I think slightly below 10 dB. The modem had ALE and provided a >SNR figure and my old ham radio ear figured an S2-3 signal. > >When we switched to 4800 bps, the DV sounded just like the individual speaking >over a telephone...better than SSB voice but it required a slightly better SNR. > >Data with the TacTerm 39 tone modem was really good...text came through at >about a page a minute with a signal that you could hear. When the signal got >down close to the noise...where you had to strain to hear it, the throughput >went down to maybe 20-30 lines per minutebut still near 100% copy (could >have been typing errors). The actual computer software was KA9Q NOS running >on a BIG military laptop computer. > >When we went to the Harris modem and 2400 BPS/4800 BPS, the copy at 2400 BPS >was about the same with a good signal but better than the TacTerm with lower >qualitity signals. > >4800 bps screemed unless the signal got below 10 dB SNR or so. > >During Operations Desert Shield and Desert Storm, the U.S. Marine Corp used a >Hughes RT-1209 and Harris AM-6545A 400 watt amplifier to make up the GRC-193A >(http://www.nj7p.org/millist/pic/grc-193.gif) used in some of the last >productions Jeeps and Humvees. Most were using a 15-16 ft fold over whip. >The whip went up just about 18" higher then the Humvee top and then tilted >over and ran horizontal the remainder of the length. This provided a good >NVIS antenna radiation pattern. > >The Marine Corp did connect the Harris MIL-STD-188-110x modem to the GRC-193 >and used a computer to send data from the field back to their command center. > >For digital voice I believe that some units used the Navy's version of the >TacTerm and some may have been using the later ITT MinTerm DV unit. The >TacTerm (KY-57) can accept signal fades of up to 12 seconds without losing >synchronization with the transmitting station. > >I never noticed any delays or words that were not understandable using the >TacTerm or MinTerm or Harris Modem using LCP-10 and UG-??? encryption unit. >There were of course a second or two between transmissions, but certainly not >enough to prevent artillary spotting or fire control. > >The PRC-109/GRC-193 systems were used at least in 1985 and perhaps before with >the TacTerm. The TacTerm was used in the Viet Nam war on HF SSB, VHF and UHF >AM and as far as I know without problems. The C-130s tracking and Navy vessel >captured by North Korea used Tacterm's on HF and the crew of the C-130 never >mentioned to me that there were communications using the TecTerm. > >So when the Marine Corp have problems with DV must have been shortly after the >capture of the USS Pubelo which I believe was in 1968. > >A good reference on the ANDVT modem may be _HF modem evaluations for the >Advanced Narrowband Digital Voice Terminal (ANDVT)_ by Chase, D.; Bello, P. >A.; Boardman, C.; Pickering, L.; Pinto, R. published in Nov 1978 > >Abstract: >"During this program, the specifications for the ANDVT HF modem have been >refined and detailed evaluation and simulation of the new technical features >within this modem have been conducted. These include a multiple-tone signal >detection format with an adaptive
[digitalradio] Re: Digital Voice: Some thoughts after one week.
--- In digitalradio@yahoogroups.com, "DuBose Walt Civ AETC CONS/LGCA" <[EMAIL PROTECTED]> wrote: > > I've heard DV using LCP-10 and a 16 tone modem as well as a 39 tone modem at 1200 bps...it sounds robotic at best. But that could have been just the systems used (ANDVT/Mil-STD-188-110) > > Walt/K5YFW Walt, Thanks for your very interesting and informative comments. I would be very interested in meeting you on the air for an extended conversation on the subject. We should be able to connect on 40M or 80M in the evenings. I often monitor 7295 +/-. I can also be reached on EchoLink. Some of the questions I have are: 1) Can you suggest a reference on HF propagation that may show distributions or histograms of fade depths, durations and bandwidths? 2) For the examples of military equipment you gave, did they use voice bandwidths (~2.5 KHz) or were the bandwidths larger? 3) With military communications I expect that voice quality and accuracy of the communication is essential. For ham weak signal applications where accuracy is not a life and death matter, can we gain any performance by trading codec data for FEC data? If voice quality at 2400 bps is considered acceptable for military applications, can we get better SNR performance with useable voice quality for ham applications at codec data rates less than 2400 bps with stronger FEC? Is there anyone reading this thread that could develop additional experimental modes for WinDRM? Ed WB6YTE Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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/
RE: [digitalradio] Re: Digital Voice: Some thoughts after one week.
I've heard DV using LCP-10 and a 16 tone modem as well as a 39 tone modem at 1200 bps...it sounds robotic at best. But that could have been just the systems used (ANDVT/Mil-STD-188-110) Walt/K5YFW -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] Sent: Wednesday, October 11, 2006 8:20 AM To: digitalradio@yahoogroups.com Subject: Re: [digitalradio] Re: Digital Voice: Some thoughts after one week. It was my understanding that the QAM-4 modulation was used for the text transmission and you needed to use at least QAM-16 for the voice. How many bps can you get through with QAM-4? If LPC doesn't work at 1200 bps, then what other codec do you suggest? Even MELP (which is a type of LPC) normally was based upon a 2400 bps speed was it not? And apparently it works OK at 1000 bps? 73, Rick, KV9U cesco12342000 wrote: > >A codec withh 1000bit/sec would allow qam-4 modulation, and improve >the robustness to "useful" levels. Tests with a 1200 bit/sec LPC >codec have been negative (bad intellegibility). > > > > Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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/
RE: [digitalradio] Re: Digital Voice: Some thoughts after one week.
Ed, Back in the fall of 1989, we started using a unit called the TacTerm for DV. The best modem was a 39 parallel tone modem (Mil-Std-188-110?) and 2400 BPS. On HF it sounded funny...robotic like...and while it did work on about the same SNR as a ~S3 SSB signal ...the SNR had to be about 10 dB, it worked much better on VHF and UHF FM as well as UHF AM. In Jan-Feb 1990, after Operation Just Cause, I got to play with a Harris Mil-Std-188-110? modem and DV at 2400 BPS AND 4800 BPS. The 2400 bps DV still sounded a bit robotic but worked quite well at S2-S3 signals and even when the SNR was at or I think slightly below 10 dB. The modem had ALE and provided a SNR figure and my old ham radio ear figured an S2-3 signal. When we switched to 4800 bps, the DV sounded just like the individual speaking over a telephone...better than SSB voice but it required a slightly better SNR. Data with the TacTerm 39 tone modem was really good...text came through at about a page a minute with a signal that you could hear. When the signal got down close to the noise...where you had to strain to hear it, the throughput went down to maybe 20-30 lines per minutebut still near 100% copy (could have been typing errors). The actual computer software was KA9Q NOS running on a BIG military laptop computer. When we went to the Harris modem and 2400 BPS/4800 BPS, the copy at 2400 BPS was about the same with a good signal but better than the TacTerm with lower qualitity signals. 4800 bps screemed unless the signal got below 10 dB SNR or so. During Operations Desert Shield and Desert Storm, the U.S. Marine Corp used a Hughes RT-1209 and Harris AM-6545A 400 watt amplifier to make up the GRC-193A (http://www.nj7p.org/millist/pic/grc-193.gif) used in some of the last productions Jeeps and Humvees. Most were using a 15-16 ft fold over whip. The whip went up just about 18" higher then the Humvee top and then tilted over and ran horizontal the remainder of the length. This provided a good NVIS antenna radiation pattern. The Marine Corp did connect the Harris MIL-STD-188-110x modem to the GRC-193 and used a computer to send data from the field back to their command center. For digital voice I believe that some units used the Navy's version of the TacTerm and some may have been using the later ITT MinTerm DV unit. The TacTerm (KY-57) can accept signal fades of up to 12 seconds without losing synchronization with the transmitting station. I never noticed any delays or words that were not understandable using the TacTerm or MinTerm or Harris Modem using LCP-10 and UG-??? encryption unit. There were of course a second or two between transmissions, but certainly not enough to prevent artillary spotting or fire control. The PRC-109/GRC-193 systems were used at least in 1985 and perhaps before with the TacTerm. The TacTerm was used in the Viet Nam war on HF SSB, VHF and UHF AM and as far as I know without problems. The C-130s tracking and Navy vessel captured by North Korea used Tacterm's on HF and the crew of the C-130 never mentioned to me that there were communications using the TecTerm. So when the Marine Corp have problems with DV must have been shortly after the capture of the USS Pubelo which I believe was in 1968. A good reference on the ANDVT modem may be _HF modem evaluations for the Advanced Narrowband Digital Voice Terminal (ANDVT)_ by Chase, D.; Bello, P. A.; Boardman, C.; Pickering, L.; Pinto, R. published in Nov 1978 Abstract: "During this program, the specifications for the ANDVT HF modem have been refined and detailed evaluation and simulation of the new technical features within this modem have been conducted. These include a multiple-tone signal detection format with an adaptive threshold, a multiple-tone/multiple-stage Doppler estimation algorithm, a matched filter frame estimation algorithm utilizing PN correlation properties, a low-rate error-correction coding approach for protection of the KG sync sequences, an error-correction coding approach specifically designed to protect the critical speech parameters, use of soft-decision (channel measurement) information obtained from the demodulator, and decision-directed Doppler tracking utilizing information from all data tones. The analytical and simulation results provide the desirable result that the preamble can be successfully received at a lower SNR than is required for the reception of high-quality 2400-b/s digitized voice." Walt/K5YFW -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] Sent: Wednesday, October 11, 2006 2:17 AM To: digitalradio@yahoogroups.com Subject: [digitalradio] Re: Digital Voice: Some thoughts after one week. Some more info: I found a paper that describes some tests done with 2.4Kbps and 1.2kbps voice transmission over HF paths. It sounds like the 1.2 kbps gives useable voice quality. I talked to a friend who h
Re: [digitalradio] Re: Digital Voice: Some thoughts after one week.
It was my understanding that the QAM-4 modulation was used for the text transmission and you needed to use at least QAM-16 for the voice. How many bps can you get through with QAM-4? If LPC doesn't work at 1200 bps, then what other codec do you suggest? Even MELP (which is a type of LPC) normally was based upon a 2400 bps speed was it not? And apparently it works OK at 1000 bps? 73, Rick, KV9U cesco12342000 wrote: > >A codec withh 1000bit/sec would allow qam-4 modulation, and improve >the robustness to "useful" levels. Tests with a 1200 bit/sec LPC >codec have been negative (bad intellegibility). > > > > Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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] Re: Digital Voice: Some thoughts after one week.
> The WinDRM specification is very sketchy .. Well,... you are invited to provide a better one. > but the FEC is not > described. The interleaving of the pilots and overhead data is > described but not the interleaving of the voice data. It says "This document describes the DIFFERENCE of mode HAM to the official broadcast DRM standard". That means everithing not described is like the official broadcast DRM standard. FEC and interleave is exactly like broadcast. More, its the same code used in the DREAM DRM software. > I will have to have a conversation with one of the speech codec > designers I work with. A codec withh 1000bit/sec would allow qam-4 modulation, and improve the robustness to "useful" levels. Tests with a 1200 bit/sec LPC codec have been negative (bad intellegibility). Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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] Re: Digital Voice: Some thoughts after one week.
Some more info: I found a paper that describes some tests done with 2.4Kbps and 1.2kbps voice transmission over HF paths. It sounds like the 1.2 kbps gives useable voice quality. I talked to a friend who had done some research for the military back in the '80s on digital voice transmission over HF. He said that the state of the art back then was about 2.4Kbps but there was a technique developed for decoding the speech into text with a very limited vocabulary for tactical operations - around 300 words - and sending the words with minimum coding required for the limited vocabulary. The transmitted data was then reconstructed into speech at the receiving end. The data rates achieved with this method were as low as 300 bps. There were a few problems with this method, though. First it introduced substantial delays due to the processing required for the speech recognition. Second, the Aussies got very upset when their speech came out the other end of the link with a midwestern accent. :) Finally, when attempts were made to apply this method to an application for the Marines for fire control communications, the Marines were unable to come up with a 300 word vocabularly that didn't contain profanity or obscenities so the project was killed. Seriously, long distance HF propagation imposes some very challenging problems with long fades that can only be overcome with long interleaving of the data which creates long delays in the transmission. I will continue to study the issue and report any interesting ideas that show promise for weak signal digitzed voice communications. Ed --- In digitalradio@yahoogroups.com, "Ed Hekman" <[EMAIL PROTECTED]> wrote: > > --- In digitalradio@yahoogroups.com, Tony wrote: > > > > Ed wrote: > > > > > Are there any communications engineers in this group that can > > > give us some idea whether a useable quality digitized voice can > be > > > sent over a 2.5 KHz wide HF channel with SNR comparable to or > less > than > > > what is required for analog voice? > > > > I was thinking about this today Ed. I'd sacrifice a bit of voice > qaulity for > > better SNR performance. > > > > WinDRM defaults to the MELP codec and I was wondering if the SPEEX > or LP-10 > > offer an improvement in SNR performance? > > > > Tony KT2Q > > Tony, > > The key to better weak signal performance will be primarily in how > the data is sent over the air. Observing the signal for digital > SSTV on 20M has been very interesting. Often a hole in the spectrum > can be observed as it moves across the spectrum. It takes out about > 20% of the spectrum and has a time span at one frequency of around a > second. The packaging of the data must be done with enough > redundancy spread throughout the spectrum so it can be recovered in > spite of these spectrum holes. On 80M atmospheric noise tends to > have short impulses that take out the entire signal for much shorter > periods of time - much less than a second. To mitigate this, the > data redundancy must be spread over time so the data can be > recovered in spite of a complete loss of signal for a few > milliseconds. > > Of course adding redundancy means reducing the data rate for the > encoded voice data. This would probably require some adjustments to > the voice coding algorithm. With cellular signals, although the > maximum data rate may be 8K bps, the effective rate is usually less > than 1/2 that due to the fact that speech is not a constant signal - > there are holes in it for short periods of time during which no data > needs to be sent. Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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] Re: Digital Voice: Some thoughts after one week.
--- In digitalradio@yahoogroups.com, "Ed Hekman" <[EMAIL PROTECTED]> wrote: > > I found the specifications. The spec used for broadcast DRM can be > found here: > > http://webapp.etsi.org/exchangefolder/es_201980v020101p.pdf > > The WinDRM spec can be found here: > > http://www.qslnet.de/member/hb9tlk/drm_h.html The WinDRM specification is very sketchy but after a quick review it suggests that the speech data rate is near the minimum possible and there is little room for additional FEC coding. The documment suggests that the minimum data rate for voice is 1000 bits per 400 ms frame (2.5 kbps). The subcarrier modulation is QAM16 or QAM64 and there are two levels of FEC to choose from but the FEC is not described. The interleaving of the pilots and overhead data is described but not the interleaving of the voice data. I will have to have a conversation with one of the speech codec designers I work with. Ed Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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/
Re: [digitalradio] Re: Digital Voice: Some thoughts after one week.
It is not so much that the package is different between voice and text modes, but rather, the amount of data flowing through the link in a given amount of time. In order to have voice transmissions with good intelligibility and no breaks in the signal, you need a VERY robust data link. The WinDRM specifications call for a minimum of 1,000 bits passed per each block of 400 msec. Anything slower than that and voice transmissions are not possible. Even if you do reduce the number of bits per unit of time needed for voice, the quality of the voice will typically suffer. And the main selling point of DV seems to be the quality of the audio. Take that away and I don't see any real advantages of DV over analog. While you can tolerate varying throughputs for text messaging, imaging, and similar data, it becomes intolerable for voice due to its real time requirements. 73, Rick, KV9U kd4e wrote: >I am puzzled as to why one digital signal works >well under poor signal conditions and another does >not. > >DSSTV and DV contain more data than the simple text common >to most digital modes, but that seems to be quantity vs kind. > >Why would image or voice content be packaged differently, >and thus be less robust than text, please? > > > Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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] Re: Digital Voice: Some thoughts after one week.
I found the specifications. The spec used for broadcast DRM can be found here: http://webapp.etsi.org/exchangefolder/es_201980v020101p.pdf The WinDRM spec can be found here: http://www.qslnet.de/member/hb9tlk/drm_h.html Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links <*> To visit your group on the web, go to: http://standraise.corp.yahoo.com/group/digitalradio/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://standraise.corp.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] Re: Digital Voice: Some thoughts after one week.
--- In digitalradio@yahoogroups.com, Tony <[EMAIL PROTECTED]> wrote: > > Ed wrote: > > > Are there any communications engineers in this group that can > > give us some idea whether a useable quality digitized voice can be > > sent over a 2.5 KHz wide HF channel with SNR comparable to or less > than > > what is required for analog voice? > > I was thinking about this today Ed. I'd sacrifice a bit of voice qaulity for > better SNR performance. > > WinDRM defaults to the MELP codec and I was wondering if the SPEEX or LP-10 > offer an improvement in SNR performance? > > Tony KT2Q Tony, The key to better weak signal performance will be primarily in how the data is sent over the air. Observing the signal for digital SSTV on 20M has been very interesting. Often a hole in the spectrum can be observed as it moves across the spectrum. It takes out about 20% of the spectrum and has a time span at one frequency of around a second. The packaging of the data must be done with enough redundancy spread throughout the spectrum so it can be recovered in spite of these spectrum holes. On 80M atmospheric noise tends to have short impulses that take out the entire signal for much shorter periods of time - much less than a second. To mitigate this, the data redundancy must be spread over time so the data can be recovered in spite of a complete loss of signal for a few milliseconds. Of course adding redundancy means reducing the data rate for the encoded voice data. This would probably require some adjustments to the voice coding algorithm. With cellular signals, although the maximum data rate may be 8K bps, the effective rate is usually less than 1/2 that due to the fact that speech is not a constant signal - there are holes in it for short periods of time during which no data needs to be sent. Can someone tell where to find the specification for the modulation format used by WinDRM? Ed WB6YTE Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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/
Re: [digitalradio] Re: Digital Voice: Some thoughts after one week.
kd4e wrote: > I am puzzled as to why one digital signal works well under poor > signal conditions and another does not. You have to define "poor conditions" somehow. It may be noise, multipath, ionospheric doppler, fading, etc. Each one produces a different impairment, depending on the modulation and coding used. And generally you have several impairments combined, on various degrees of severity, to make it even "more interesting". Without a proper characterization, the results can be very confusing. One of the fortunate phrases of Lord Kelvin states that you must express magnitudes numerically to be able to grasp their meaning and leave fuzziness aside. Doesn't mean it may be easy 73, Jose __ XIII Convención Científica de Ingeniería y Arquitectura 28/noviembre al 1/diciembre de 2006 Cujae, Ciudad de la Habana, Cuba http://www.cujae.edu.cu/eventos/convencion Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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/
Re: [digitalradio] Re: Digital Voice: Some thoughts after one week.
> Even though I am not an engineer, we know from P-25 that digital voice > transmissions drop out before analog completely goes into the noise and > it is my understanding that the narrowest BW they use is 6.25 KHz. And > that is primarily for VHF/UHF frequencies that do not have the problems > we have on HF bands. > > Since we are not likely going to be able to use wide BW HF signals here > in the U.S., I really don't see DV being used that much on HF. It may be > used more on the higher bands, but even then there MUST be some > advantages to this new technology, other than just being new. Typically, > you move toward new technology when it is either faster, lower cost, > higher quality, or some combination of these and perhaps other > attributes. Digital signals can offer this with text transmission > (PSK31, MFSK16, Olivia, etc.) but it may not be able to offer benefits > for amateur HF which operates very differently from what a non-technical > user does on the commercial/military frequencies. Digital signals are > limited by the science behind this technology and we can not change that > unless some new breakthrough occurs. > > 73, Rick, KV9U I am puzzled as to why one digital signal works well under poor signal conditions and another does not. DSSTV and DV contain more data than the simple text common to most digital modes, but that seems to be quantity vs kind. Why would image or voice content be packaged differently, and thus be less robust than text, please? -- Thanks! & 73, doc, KD4E ... somewhere in FL URL: bibleseven (dot) com Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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/
Re: [digitalradio] Re: Digital Voice: Some thoughts after one week.
Tony wrote: > Ed wrote: > > > Are there any communications engineers in this group that can give > > us some idea whether a useable quality digitized voice can be sent > > over a 2.5 KHz wide HF channel with SNR comparable to or less > > > than what is required for analog voice? > > I was thinking about this today Ed. I'd sacrifice a bit of voice > qaulity for better SNR performance. > > WinDRM defaults to the MELP codec and I was wondering if the SPEEX or > LP-10 offer an improvement in SNR performance? > > Tony KT2Q Whatever you do to reduce the data rate will help. All digital communications require signal levels strong enough to overcome a certain threshold, and it is difficult it will beat analog (SSB) that has no threshold. Actually, there is a threshold on the operator's brain, and makes the difference between a capable, or well trained operator, and the rest of the population. FEC helps, but requires more bandwidth, due to the redundance it adds. Maybe a judicious choice of coding can help, to get as close as possible to the Shannon limit. But there may be a tax on computing power... Codecs can make a difference, the tradeoffs generally are are readability, latency, and tin man tone of voice. Again, many may agree on the good quality ones, but as you sacrifice voice quality, not everyone will be able to copy well. So, it is not a simple matter to lower the threshold, and mantaining wide acceptance on a 2.4 kHz HF channel. YMMV, Jose, CO2JA __ XIII Convención Científica de Ingeniería y Arquitectura 28/noviembre al 1/diciembre de 2006 Cujae, Ciudad de la Habana, Cuba http://www.cujae.edu.cu/eventos/convencion Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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/
Re: [digitalradio] Re: Digital Voice: Some thoughts after one week.
Even though I am not an engineer, we know from P-25 that digital voice transmissions drop out before analog completely goes into the noise and it is my understanding that the narrowest BW they use is 6.25 KHz. And that is primarily for VHF/UHF frequencies that do not have the problems we have on HF bands. Since we are not likely going to be able to use wide BW HF signals here in the U.S., I really don't see DV being used that much on HF. It may be used more on the higher bands, but even then there MUST be some advantages to this new technology, other than just being new. Typically, you move toward new technology when it is either faster, lower cost, higher quality, or some combination of these and perhaps other attributes. Digital signals can offer this with text transmission (PSK31, MFSK16, Olivia, etc.) but it may not be able to offer benefits for amateur HF which operates very differently from what a non-technical user does on the commercial/military frequencies. Digital signals are limited by the science behind this technology and we can not change that unless some new breakthrough occurs. 73, Rick, KV9U Ed Hekman wrote: >I work in cellular communications and know that good voice quality >can be maintained with a data rate of 8k bps. It seems reasonable >that useable voice quality can be produced with half that data >rate. Are there any communications engineers in this group that can >give us some idea whether a useable quality digitized voice can be >sent over a 2.5 KHz wide HF channel with SNR comparable to or less >than what is required for analog voice? > > > > > > Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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/
Re: [digitalradio] Re: Digital Voice: Some thoughts after one week.
Ed wrote: > Are there any communications engineers in this group that can > give us some idea whether a useable quality digitized voice can be > sent over a 2.5 KHz wide HF channel with SNR comparable to or less > than > what is required for analog voice? I was thinking about this today Ed. I'd sacrifice a bit of voice qaulity for better SNR performance. WinDRM defaults to the MELP codec and I was wondering if the SPEEX or LP-10 offer an improvement in SNR performance? Tony KT2Q Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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] Re: Digital Voice: Some thoughts after one week.
--- In digitalradio@yahoogroups.com, "Andrew O'Brien" <[EMAIL PROTECTED]> wrote: > > I have been "QRV" on digital voice ,using WinDRM, and thought I would offer > some rookie/newbie random thoughts. > > 1. This mode's performance may appear counter-intuitive for most digital > mode operators. By that I mean, we associate digital modes like PSK31, > Olivia, MT63, etc, with the ability to communicate under weak signal > conditions. To be able to communicate when SSB analog voice signals are not > reliable. > > It is the opposite with Digital Voice , as manifested in WinDRM. Perfectly > copyable CW and traditional SSB voice signals do not translate in to enough > signal to maintain the digital voice transmissions. e.g. my analog QSO > today with Gerhard OE3GBB was about a 449 RST. That is; Readable with > practically no difficulty, Fair signals . However, I had to focus my brain > quite a bit to pick his voice out between the QRM. When we switched to DV, > the audio was stunning in quality (better than FM on 2M) but I only copied > about 40% of what he sent, the rest was just silence. So, I am not sure > what "use" this communication method has if we need "good" signals rather > than fair or weak signals. If one can copy a person fair to well with SSB > analog, why do we need to switch to DV voice? > > > 2. The software (WinDRM) is very well designed and fairly easy to figure > out. The ability to have the software switch Mic/Line In settings in the > sound mixer is very useful. The waterfall and other tuning display > indicators are extremely well thought out. > > > 3. There is something "odd" about copying HF signals with good audio > fidelity. My old ham brain is so used to "Donald Duck" under water SSB > audio that hearing a DV signal does not sound like "real radio". It IS real > radio because it is sent/received via radio waves , but it feels like you > are on Echolink , IRLP, or Skype!. > > > 4. It is exiting to be on air with just the few that are active. If you > expect to hear LOTS of DRM signals, you'll be disappointed. Activity is > less than Hell or MT63! > > 5. WinDRM shows that DV can be done well without expensive outboard hardware > devices (AOR). It works with a fairly low CPU PC. I think we are in the > Betamax-VHS era for amateur radio digital voice, with several incompatible > DV modes. > > > Andy K3UK Andy, I've had some of the same thoughts. Much of the attraction of Ham radio to a lot of people is the ability to work long distances. CW still lives and PSK31 has been widely accepted because of this. It was quite a thrill when I worked someone in Russia with PSK31 who was using a homebrew rig with 5 watts output. PSK31 has opened Ham radio to a lot of people who can't put up a big antenna or run high power. When I first tried analog SSTV a few months ago I thought about how primitive it was compared to digital communications today. However when I tried HamPal it was very disappointing to find out how difficult it was to receive a picture even with an S9 signal. The picture quality is stunning but the success rate is so low that it will never replace analog SSTV. I had hoped that DV would be able to improve the quality of communication over analog voice in conditions when analog voice was marginal. It seems that if we could trade some of the voice quality for better weak signal performance it would be much more attractive to many hams. With SSTV, weak signal performance could easily be improved by reducing picture resolution and reducing the data rate. That is a little more difficult to do with voice since voice communications must be in real time - we can't just slow the data rate down to fit the channel conditions. I work in cellular communications and know that good voice quality can be maintained with a data rate of 8k bps. It seems reasonable that useable voice quality can be produced with half that data rate. Are there any communications engineers in this group that can give us some idea whether a useable quality digitized voice can be sent over a 2.5 KHz wide HF channel with SNR comparable to or less than what is required for analog voice? Ed Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) 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
