Thanks for your comments, Jose, however, I think most of us understand and agree with what you say.
What I am not clear on is the difference betwee the differential versions of the PSK modes and the non-differential versions. For example, my understanding is that PSK31 is really DBPSK31. I think perhaps QPSK is DQPSK? Are there cases where QPSK and higher order modulation does not use the differential form? Is the multitone modem using 41 parallel tones similar to the MIL/STANAG modems? Do you consider the STANAG modems running at multithousand baud rates as described by some of the ALE folks? Or is this a case where there is a difference of the definition? You can get very high bit rates from using multiple tones and with higher order modulations schemes such as what Pactor uses. But the claim by the ALE proponents is that we need much higher baud rates than only 300 baud in order to use the STANAG type modems because they run at speeds that exceed 1000 baud or more and are successfully used on HF. Presumably on the lower bands as well as the upper HF bands. Can you or anyone explain why they need this high speed on HF when even 300 baud is pushing the limit on the higher HF bands? 73, Rick, KV9U Already in 1991 there was a 41 parallel tone modem being tested in transatlantic paths...it was capable of running 4800 bit per second and sometimes, up to 9600. Jose Amador wrote: >--- KV9U <[EMAIL PROTECTED]> wrote: > > > >>Walt, >> >>Maybe someone can clear this up, but what is the >>difference between the >>differential modes such as DBPSK, DQPSK, 8DPSK, and >>16DPSK such as used >>with Pactor 2 and modes such as 8QPSK, 16QPSK? >> >> > >Even when theory says that differential modes have a >worse BER, seemingly they work better on ionospheric >paths, as with a moving ionosphere, is difficult to >maintain an absolute phase reference. > > > >>With the former, it is my understanding that with a >>single tone, the >>binary form (DBPSK) gives you one bit/second, DQPSK >>two, 8DPSK three and >>16DPSK four. >> >> > >Still holds true... > > > >>With the previous discussions on baud rate for the >>STANAG and MIL >>modems, can we still say that HF should use baud >>rates below 45? >> >> > >Depending on multipath, which is worse on lower >frequencies. > > > >>The claim is that these modems appear to be able to >>use extremely high >>baud rates, well above even 300 baud on HF and still >>work well under >>difficult conditions. >> >> > >The game is using many slow channels in parallel. > >Already in 1991 there was a 41 parallel tone modem >being tested in transatlantic paths...it was capable >of running 4800 bit per second and sometimes, up to >9600. > > > >>In fact, the ALE folks believe that amateur radio >>is being held back on HF because we can not transmit >>in excess of 300 baud on most HF frequencies. >> >> > >Signalling rate....the speed at which every tone is >wiggled. Actually, the ionosphere imposes a much >lower rate for succesful transmission on the lower >frequencies. > > > >>Even Pactor does not exceed 200 baud and that is >>only under the best of conditions and even at 100 >>baud, the claim by Dr. Rink was that "The >>short term time jitter has a magnitude of up to 5 >>msec. Larger time smearing can only be observed >>under very special conditions of the >>ionosphere. A baud rate of 100 symbols per second >>has proven to be low enough for almost all possible >>propagation conditions, especially if >>powerful error control coding is applied. >> >>Is there anyone here who can further explain this? >> >> > >Once again....Pactor can adaptively switch from 100 to >200 baud and back...be either Pactor I, II or III. >Additionally, it can adaptively switch in and out >constellation complexity and quantity of tones. Using >compression, FEC and the whole boxful of coding >tricks, it can go up to 5200 bits per second. I have >seen it >on Pactor III ocassionally running up to 3600 bps on >40 meters, and more often, 2800 and 1400 bps. > >73 de Jose, CO2JA > > 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/
