Rick, To me it all depends on "the channel behavior". On HF, with multipath, the parallel modem wins because the simbols can be made longer than the delay spread.
Just observing the succesful implementations may lead anyone to see that in an ionospheric channel, generally, parallel tone modems wins. There are many examples, like the Thales parallel tone modems, DRM, WinDRM, the russian ninetysome tones modem, etc. On HF, a serial modem can only have an edge close to the MUF, which is a dwindling parameter.... I used 1200 bauds Bell 202 packet links for BBS forwarding on HF (20, 15 and 10 meters), and did generally well on 10, most of the times on 15 and sometimes on 20. On 20, there were excellent days, and very bad days with almost nil thruput. Pactor II achieves 10 times the thruput of a 300 baud link, on 20 and 40 m, consistently. Even for moonbounce and tropo, parallel tones have an edge. The PUA43 protocol, JT44, JT65, etc, do have an edge. I would have to reread the manuals, since I was interested on that too but real life commitments, hurricanes that forced me to take down the antennas , etc, have had negative effects on my wishlist. And believe it or not, I have found that the safest place for an antenna is in top of a mast. Down at chest level, it is very easy for anyone to inadvertently get tangled in the wires and rods and do the damage that you intended to avoid the hurricane to do....8-( Jose, CO2JA KV9U wrote: > When I make the statement that there is not much difference between > the parallel and serial modems, I should have clarified this in terms > of the performance results. In other words, you could have either one > with similar results. According to one source: > > http://www.argreenhouse.com/society/TacCom/papers98/11_04i.pdf > > The tradeoffs are such that the serial modem requires equalization > and robust error correction, but can give you similar results to the > parallel modem. But eventually, the parallel modem may outperform > the serial modem. > > It seems that it is Bonnie's contention that these high speed serial > modems are the advanced kind of technology we need on amateur radio. > > But it just seems that we already have an equivalent modem to the > high speed serial modem with our parallel modems that are able to run > with similar speeds due to multiple parallel tones vs. a high speed > serial tone. Not that I oppose high speed serial modems. I question > whether they really are an advance over what we already have. > > 73, > > Rick, KV9U __________________________________________ 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
