Rick, You asked..."Why do the Pactor modes work so well? They have the same bandwidth, power, and fairly similar coding to sound card modes. Is their coding something that can not be implemented on current sound cards in terms of the modulation?"
Here may be part of the answer... Measurements made by Rick, KN6KB, when working on SCAMP measured PI/II/III with the KC7WW HF Channel Simulator found that PIII at a -10 dB SNR had a slightly better throughput than MT63. MT63-2K has been measured by KC7WW using the same simulator that he sold KN6KB and found that MT63 needed a about a 5 dB better SNR than Pactor III to have the same throughput. The problem with MT63 is that it does not change its modulation dynamically as the SNR changes but Pactor III does. So when conditions are good, Pactor III screams. But when conditions are very poor, Pactor III is not that much better than MT63. Another thing is that MT63 doesn't use ARQ and Pactor does. Also, the modulation rate is lower than optimum for all of the HF bands...31 Hz. Research for the past 30 years has reveiled that a 45-50 baud modulation rate works very well on HF. Thus if MT63 kicked up its modulation rate and added ARQ, it might very well outperform Pactor III and low SNRs. If you added dymanic modulation changes to MT63, you might very well have a throughput of 400-800 WPM. A typed page is about 720 words. Copy some E-Mail into your word processor some time and do a word count...you might be surprised. 73, Walt/K5YFW -----Original Message----- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] Sent: Wednesday, August 23, 2006 1:57 PM To: digitalradio@yahoogroups.com Subject: Re: [digitalradio] The digital throughput challenge on HF Mark, Why do the Pactor modes work so well? They have the same bandwidth, power, and fairly similar coding to sound card modes. Is their coding something that can not be implemented on current sound cards in terms of the modulation? P2 is a variable DPSK mode and P3 is OFDM are they not? 73, Rick, KV9U Mark Miller wrote: >You have pointed out a basic principle with respect to data >throughput. Throughput is a function of bandwidth, power, and >coding. With amateur HF we are power, and bandwidth limited. The nature >of the media we are opening in makes forward error correction a must, thus >we suffer a loss of throughput because of coding. The very robust modes >like MT63 and Olivia require interleaving and convolutional >coding. Compare MT63 and Olivia with RDFT or amateur DRM. RDFT and DRM >are great modes, but requires a fairly high S/N ratio. The challenge is >there, but the solution is far from easy. > >73, > >Mark N5RFX > > > > 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/ <*> 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/
