I earlier mentioned ARQ in real time, but if you use the programming technique that KN6KB used when he developed SCAMP, (Sound Card Amateur Messaging Protocol), he used RDFT. While this was not practical to decode during each cycle, he was able to work in the background with the past packet that was received and do the necessary processing.
This almost completely avoids any issues with latency, unless the latency exceeds the cycle time. I suspect that someday this will be the approach taken for the newest sound card modes. Before he came up with this technology, others were basically saying it could not be done. But he did figure out a sophisticated way to do it. One other thing that Pactor modes have proven rather well to me, is that a two tone system, separated by some distance will give you one of the most robust modes possible by adding in some redundancy/FEC, etc. In my location, there is no misconception about working close to the atmospheric noise level. Right now on my ICOM 756 Pro 2, the S meter readings are: Preamp off: 160 S-1, 80 S0, 40 S0 to S4 due to static crashes from storm, 30 same as 40, 20 S0 Preamp on at maximum (second step): 17 meter through 6 meters S0 With better antennas, this would be stronger on the higher bands and with more propagation. Of course I sometimes have a locale RFI problem (TV, and something else that I have not figured out on the lower bands). Typically, my main loss of contact with other stations (not including Pactor or wide mode ALE signals coming on top of my frequency) is because they fade into the noise. And QSB can be difficult unless you have an ARQ mode. I have seen some multiipath, especially when I have tested PSK31 on VHF, but much of that was from aircraft. I am not sure how I can discern multipath when on HF. Is there any clue in the waterfall or do you go by the sound? 73, Rick, KV9U Rein Couperus wrote: > All high-latency modes are unsuitable for ARQ. > > A persistent misconception is that you would be using signals near the noise > level. > As I have stated many times, noise is hardly ever the problem unless it is S8. > The problem is multi-path causing QSB (up to 80 dB on path we are using) and > QRM from other > stations firing up their gear on top of your QSO. > > PSkmail arq takes care of this very well by repeating the stuff that has been > unreadable in the qsb. > QRN is taken care of by automatically shortening of the packets when the > error rate goes up, which > decreases the chance of a packet being hit. > > Again, noise is seldom the problem, we pick a better path if necessary, > depending on time of day. > Signal levels are normally around S5-S9 here in EU, depending on > time/distance. > > 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 <*> 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/
