--- DuBose Walt Civ AETC CONS/LGCA <[EMAIL PROTECTED]> wrote: > Ok Jose and everyone...let's take a poll or have > some SWAGs. > > So what do YOU (plural) think is the best modulation > technique to use for a NEW and BETTER HF data mode?
I believe there is no single best mode. Like in antennas, that you must trade gain for F/B, seems to me you must trade speed and BER depending on the channel conditions at a particular moment. Taking adventage of SCS experience, they chose PSK (cannot tell by heart if differential or not, a peek to the manual is needed) as a modem, and depending on the retry rate (closely related to BER) it tries more complex constellations and more carriers. One of the "secrets" is the switchover criteria...when retries rise, then jump to the next "lower speed", whatever it means. Maybe it could take some experimentation to decide which modulation format, other than a single one (PSK) would be advisable for low frequency, noisy bands. There, MFSK seems to have an edge. So far, I have seen no "adaptativeness" in MFSK modes. I believe, based on what I have seen on MFSK and Olivia, that a slow channel with no retries could be a good solution when other solutions fail. So, I see at least two different scenarios. Clean bands, closer to the MUF, and dirty bands, close to the LUF. > PSK > QPSK > DBPSK > DQPSK (Dairy Queen PSK...Dairy Queen is an ice cream > franchise) > 8DPSK > DQPSK > 8QPSK > 16QPSK > > And by the way, the Russians have a 96 tone HF data > mode that is suppose to have great throughput, is > very robust and is wider than 4 KHz. They love big, either it be trucks, planes or rockets.... > Concerning baud... > > If the MUF is 32 MHz, then I believe that it is > reasonable to think that 300 or 400 baud might work > well on 10M...but on 40M and 80M it flat won't work. On 10 and 15 meters, 1200 baud works like a charm. > So at 40 and 80M we will probably find that 45.5 > baud works rather well. Some might suggest that 31 > baud is better. I remember some newsgroup mails regarding using the PK-232 at 100 baud with packet. If it had become more common, maybe it would have bought HF packet a longer lease of life. > I don't know how we can really find out what baud is > best for each band and even if we want to. Maybe we > want to take a SWAG and have a different baud for > every band? That's probably a bad idea. But what > about 31 or 45 baud for 80-20M, 90 baud for 30M-15M > and 200 baud for higher bands...we can make the baud > rate manual or automatically selectable. For a > basic or start, I would recommend manually selecting > baud rates. I recommend automatic...SCS has proven it can be done. The switchover criteria must be identified. > My gut feeling is to start slow...play it safe to > start with...31 or 45 baud all bands. Choose a good > modulation technique...one that where you can manage > the detection. Choose a method of FEC and add ARQ. > You can see if you get better quality (error free > copy) with or without ARQ, with or with FEC, etc. I would say that in lack of a better method, gut feelings are better than no feeling at all...your proposal seems reasonable and agrees with what I have seen. ARQ is NECESSARY for message integrity. FEC may or may not be necessary, depending on the channel conditions. Unneeded FEC will lower the thruput, while properly applied FEC will save retries. > Choose a standard test text for testing and of > course make sure that the chat mode works because > after all, we DO (at least most hams) like to chat > at bit. > > The KEY to any adventure is to have a goal and the > flexibility to make changes as you go and work with > as many as you can to evaluate what you create. I would call that evolution.... > Once a mode have shown what it can do, i.e. > established its capability, then change to some > other configuration. AND REMEMBER, IT NOT A BAD > THING TO FAST FAIL A BAD IDEA. Ask Werner von Braun about it.... > If something doesn't > work as good as you have, deep six it...don't carry > on with a bad idea. Its not a bad thing to say that > you idea didn't work. It avoids losing time on a failed theory. > Those who are very technically astute, you will have > to bring things such as throughput, and robustness, > etc, down to terms that everyone can relate to. > > How about it? Are we (hams), as a group, up to > creating a better communications mode? > > I know we can. > > 73, > > Walt/K5YFW 73 de Jose, CO2JA __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.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! 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