Hi Mark, The ARQ is really important. You really should have this for serious messaging via RF and must have it if you want to interface with a mailbox system or internet. Even one bad character trashes everything when negotiating a menu. Those who are OT's with Amtor know what I mean. I used to be so frustrating trying to use Amtor even though signals were still fairly good but you could not get anywhere with a message storage bbs as there were slight errors at the edges of what Amtor could still operate. Amtor was not a very good ARQ mode when condx got a bit bad. Pactor I did not seem to have this problem. It would just fail, even with signals still observable by ear.
With ARQ, you can work deeper into the noise and still get some traffic through. My preference is to have modest FEC and then the ARQ. It amazes me that hams and especially developers are not truly excited about this. Rick, KN6KB has shown the way to get a pipelined ARQ method and eliminate the bottleneck that everyone claimed made ARQ not possible on PC's. I realize that there are only a few dozen hams who have the knowlege and can actually do this, but it only takes one to make it happen. I can not describe the thrill I got when using the beta SCAMP software. It is just so cool to watch something work so well from a soundcard at modest signal strengths. All we need is a bit lower (-5?) S/N mode that can scale upwards when condx are good enough and yet scale downwards when you have to in order to get some throughput. I am not very knowledgeable on CRF (Crest Factors). Can you give us an idea of converting peak power/average power into CRF? My understanding is that Pactor 2 has a CRF of 1.45 and if I understand things correctly, many of the raised cosine modulation schemes are similar. Am I correct that the rectangular waveforms have a CRF of 1 since square waves have a crest factor of 1? I understand that Pactor 3 has quite a variable CRF depending upon the number of tones: 1DBPSK = 1.9 3 DBPSK = 3.1 6 DBPSK = 5.7 Meanwhile, MT-63 has a large ratio between peak and average power. So that means it has a very high crest factor? 73, Rick, KV9U Mark Miller wrote: >>Note also in Figure 6, the real world test by using distance on 80 >>meters daytime. The worst performance was by Amtor, followed by Pactor 1 >>and closely by PSK31. The best performer was RTTY at these slow speeds >>and he gives his explanation as why he believes this occurs. It sounds >>reasonable to me. >> >>And also note that the non-ARQ modes always had some errors and the ARQ >>modes were error free. >> >> > > >Rick, > >If I boil your argument to 2 points it would be that the advantages of the >Pactor modes are ARQ and low crest factors? > >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 <*> 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/
