Hello Rick, RR for all.
> developing a similar sound card protocol for emergency use. It does not I've never been implicated in emergency use and I don't know what are the needs. For example, what is the net absolute throughput required in bits/sec? Examples: * Pactor 2 in the most robust scheme: Total bit rate: 200 bits/s, net absolute: 100 bits/sec * ARQ FAE in ALE400: Total bit rate: 150 bits/s, net absolute: 75 bits/sec. For 63 characters length message, the use speed (compressed) is 87 wpm. * Pactor 2 in the worst robust scheme: Total bit rate: 800 bits/s, net absolute: 700 bits/sec For files exchange, even 700 bits/sec is not sufficient, so I suppose that it is only exchanged texts or mails? > If a similar medium bandwidth (500 Hz) 2 tone PSK mode was invented for > sound cards, using the tone swapping approach of P2, it would increase This scheme does not give a very good minimum S/N (perhaps -7 or -8 dB). About the minimum S/N of Pactor 2, do you know the exact figure? (I don't speak of the SCS figure) 73 Patrick ----- Original Message ----- From: "Rick W." <[EMAIL PROTECTED]> To: <digitalradio@yahoogroups.com> Sent: Thursday, August 14, 2008 5:04 PM Subject: Re: [digitalradio] Crest factor in Pactor and other considerations > Considering the success that Pactor 2 has had, with what is one of the > more bandwidth conserving modes available with very good throughput and > yet only a 500 Hz bandwidth, this may be a "target" to meet by > developing a similar sound card protocol for emergency use. It does not > need to be the exact same protocol as P2 and probably would be better if > it was not, so no one can claim some kind of copyright infringement. > > I am not sure if operating 100 baud all the time, as P2 does, is the > best approach. as I suspect that there are times that Pactor modes (both > the early FSK and later PSK versions) don't work at all when some sound > card modes would be able to get through, even if at a very slow speed. > > If a similar medium bandwidth (500 Hz) 2 tone PSK mode was invented for > sound cards, using the tone swapping approach of P2, it would increase > robustness for certain kinds of conditions where one tone is > obliterated, but the other tone gets through, even if the overall > throughput is halved. You would still have the same crest factor > depending upon the number of simultaneous tones, but by keeping the > simultaneous tones to a small number, you would have the lowest possible > crest factor with the most robust modes and yet have higher speeds. Even > P3 is a two tone BPSK100 mode in its most robust form. Thus, even if we > did not use adaptive speed levels for the changing ionospheric > conditions we would likely focus on the more robust capabilities but > still with moderately good speeds. > > It will be interesting to see what the new sound card mode of Winlink > 2000 will be. > > 73, > > Rick, KV9U > > > > > > Patrick Lindecker wrote: >> Hello all, >> >> I was reading the general specifications of Pactor and I note a >> curious feature. >> >> The first mode of Pactor 3, with 2 carriers (in BPSK) specifies a >> crest factor of 1.9 dB (ratio of 1.55). >> Pactor 2 specifies a crest factor of 1.45 (in ratio)...1.6 dB >> >> Meanwhile, Pactor 2 applies a root raised cosine window which gives >> for a one carrier only, a crest factor of about 1.4 /1.45. >> Now in Pactor 2, with two carriers sent in the same time, mecanically >> the crest carrier must be increased to 1.6+3=4.6 dB if no overloading >> is accepted (and it would be curious to apply a cosine window to >> afterwards overload the signal...). >> >> One more information: in Pactor 3, it is written about "crest factor": >> "without signal clipping or limiting". Even if I don't see the >> difference between "clipping" and "limiting", it seems clear that they >> can send two carriers in the same time (and certainly moduled with >> independant information), without the 3 dB of penalty, which is quite >> interesting! >> >> Has someone information about the way used by SCS (Pactor company) to >> avoid or to limit this penalty? >> >> 73 >> Patrick >> >> >> > > > > ------------------------------------ > > Announce your digital presence via our Interactive Sked Page at > http://www.obriensweb.com/sked > > Check our other Yahoo Groups.... > http://groups.yahoo.com/group/dxlist/ > http://groups.yahoo.com/group/contesting > http://groups.yahoo.com/group/themixwgroup > Yahoo! Groups Links > > > > >
