Mark Miller wrote: > The wider bandwidth of PIII may make the transmission more robust.
Not only so, mainly it is the effect of constellations that have been chosen. Pactor II uses DBPSK, DQPSK, 8DPSK, or 16DPSK over two tones. Pactor III uses DBPSK or DQPSK over up to 18 carriers separated 120 Hz keyed at 100 symbols per second. Going to less complex constellations achieves more robustness, by increasing the distance between the constellation points, making the modulation less affected by noise and IMD. Of course, some other tricks may be applied. At the lowest speeds, P II repeats the data in both carriers to dodge QRM and selective fading. It allows a sort of frequency diversity. I am not aware of the tricks that P III may be using along that line, but at larger intercarrier spacings may allow even larger diversity gains. Using more complex constellations on P III (not a choice for the designers) might achieve even larger speeds. Also, at least on the lower bands, it is statistically unlikely, which might justify the choice of using only the simpler constellations. 73 de 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/
