One of the main interests that I have in digital modes is getting a message through the most difficult conditions, completely intact as sent, and as fast as possible. I was looking at the STANAG 5066 specifications and test results, (Steve has some below), and quite frankly I am concerned that this standard has what I would normally consider to be unacceptable performance (non performance) with weak signals.
I am not sure what kind of cps or wpm throughput the bit rates mean but it I wonder how it compares to SCAMP running at 10 db S/N? Because SCAMP only operated down to about +10 db S/N (maybe slightly better), it was rejected as unacceptable for practical messaging. From the info on Steve's site: http://www.n2ckh.com/MARS_ALE_FORUM/MIL-STD-188-110B.pdf Here are some claimed performance levels: Bit rate Multipath SNR BER 4800 2 ms 27 db 1 x e-3 with .5 Hz fading BW 2400 2 ms 30 db 1 x e-3 with 5 Hz fading BW 1200 2 ms 11 db 1 x e-5 with 1 Hz fading BW 300 5 ms 7 db 1 x e-5 with 5 Hz fading BW 75 5 ms 2 db 1 x e-5 with 5 Hz fading BW Even with the slowest 75 bps, and a multipath of 5 ms, it can only work down to 2 db ABOVE the noise! This is not good. From personal experience, it is not easy to get even 10 db S/N signals with typical amateur signals with modest antennas on the lower bands. They even show some constellations at 64 QAM. From what the SSTV folks have said, 64 QAM is not really a useful mode on HF. Perhaps that is because they are not using ARQ? Note also that the multipaths are moderate to low compared to worst case HF propagation. I question whether this stuff can work under many conditions we routinely operate with sound card modes (but are not 100% copy without ARQ). The BER that this system can handle seems to indicate that the channel has to be rather good. These BER's seem to be more appropriate for what we would expect on equipment designed for VHF and up ... aren't they? For those of you who have used STANAG 5066 waveforms, what kind of throughput have you experienced with real world connections? The deeper I examine this NATO standardized agreeement, the more it is beginning to look like another one of those "the emperor has no clothes" findings. Thanks and 73, Rick, KV9U Steve Hajducek wrote: >I recommend that to answer all of your technical questions on subject >ALE that you refer the actual Federal, Military and STANAG Standards >which you can find on the Internet quite easily. You can start with a >number of them at the following URL: >http://www.n2ckh.com/MARS_ALE_FORUM/tecref.html > >Listed below are the "ALE Operational Rules" taken directly from >"MIL-STD-188-141B APPENDIX A", take the time to read this and do >additional research WRT the details of the referenced items herein >and you should be satisfied that ALE is the most courteous digital >mode with automatic operation you could ever want to see, compared to >any other system that has ever been used on the Amateur Radio bands. > >/s/ Steve, N2CKH/AAR2EY > >A.4.4 ALE operational rules. >The ALE system shall incorporate the basic operational rules listed >in table A-V. Some of these >rules may not be applicable in certain applications. For example, >"always listening" is not >possible while transmitting with a transceiver or when using a common >antenna with a separate >transmitter and receiver. > >TABLE A-V. ALE operational rules. >1) Independent ALE receive capability (in parallel with other modems >and simular audio receivers) (critical). >2) Always listening (for ALE signals) (critical). >3) Always will respond (unless deliberately inhibited). >4) Always scanning (if not otherwise in use). >5) Will not interfere with active channel carrying detectable traffic >in accordance with table A-I (unless this >listen call function is overriden by the operator or other controller). >6) Always will exchange LQA with other stations when requested >(unless inhibited), and always measures the >signal quality of others. >7) Will respond in the appropriate time slot to calls requiring >slotted responses. >8) Always seek (unless inhibited) and maintain track of their >connectivities with others. >9) Linking ALE stations employ highest mutual level of capability. >10) Minimize transmit and receive time on channel. >11) Automatically minimize power used (if capable). >NOTE : Listed in order of precedence. > >TABLE A-I. Occupancy detection probability (2G and 3G). > >Waveform SNR (dB in 3 kHz) Dwell Time (s) Detection Prob > >ALE 0 2.0 0.80 > 6 2.0 0.99 > >SSB Voice 6 2.0 0.80 > 9 2.0 0.99 > >MIL-STD-188-110 0 2.0 0.80 >(Serial Tone PSK) 6 2.0 0.99 > >STANAG 4529 0 2.0 0.80 > 6 2.0 0.99 > >STANAG 4285 0 2.0 0.80 > 6 2.0 0.99 > > > > > >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! 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