Thanks for the return comments, Tony, and especially all your work in helping us understand these modes better. I have been looking at the data and comparing baud rate which directly relates to the length of symbol and I suspect that many of what we thought of as the most sensitive modes may, depending upon design, work poorly with anything other than calm ionospheric conditions. The MT-63 minimum S/N varies considerably depending upon the width of the signal which is how I came up with the comparison. Because of the redundancy in MT-63 you do get amazing ability to withstand what would otherwise be an obliterated signal. But the price is a very wide bandwidth mode that unfortunately causes QRM too. Imagine if everyone who is using PSK31 switched over to 1K or 2K MT-63. It would be very difficult to operate in the narrow area we have for text digital modes. I try and use only 500 Hz and narrower modes that I consider to be appropriate for HF use, unless the bands are severely disturbed and there are few other stations on at the time.
Do you or any other group members have any experiences with comparing the lightning static abilities of MT-63 (various widths) to THOR and the new MFSK modes that are designed into the fldigi program? I did a recent comparison of MFSK16 on fldigi and Multipsk but found roughly the same results, even on very noisy circuits. I plan to do more testing. Does anyone know the difference between MFSK31 and MFSK32? THOR appears to be Domino EX with FEC. How does this compare to Multipsk's Domino EX/FEC? Are they similar but too different to intercommunicate? Finally, Tony, do you think that you could eventually do additional testing to measure what parameters are the cut off point for the various modes? I don't know enough about ionospheric disturbances to know if you can only have Doppler (such as polar flutter) without having multipath at the same time. I seems reasonable that you might have one or the other, but most times (as you have tested) you have some of each. This would be a rather large undertaking but it seems to me that it would be very valuable to know just how the modes drop off for various levels of Doppler and multipath. So you would know that 5 msec is the most you can handle for a given mode, or 3 Hz Doppler. And then to make it even more complicated, where is the drop off point for various combinations? Is this something you could do at some future time? That way, we would have even more revealing comparison of modes and what they can and can not do under increasing difficult conditions. 73, Rick, KV9U Tony wrote: > Rick, > > > The reason that I use various modes is to discover those that work the > > best for most conditions on a given band and maintain a reasonable > > throughput > > I agree. Knowing which modes perform well when conditions deteriorate > is helpful. I complied the digital mode HF simulations for that reason. > > >The MT-63 mode seems well suited for moderate speed (50 to 200 wpm) > > under conditions with periodic interference where a part of the data > is obliterated > > The 1K mode does seem to recover well from lightning static and prints > well when QRM'd. It doesn't seem to mind when other MT63 signals > overlap by 25% or so either. That's something most digital modes can't > do. > > > It needs a much stronger signal than some other modes in order to do > this by perhaps 5 to 10 dB > > The simulator says that MT63 has a minimum SNR of -8db for 100% > throughput. That's about 2db less than PSK31 and about 6db less > than MFSK16. > > If you place an RTTY signal over the top of MFSK16 or PSK31 > signals, they will stop printing. MT63 will keep going. Of course, > it's a much wider mode and has lots of redundancy. > > > isn't it fair to say that MFSK16 is about the best choice for > robustness, > > bandwidth, and speed for keyboarding? > > I think it is a well balanced mode. I also think it's hard to beat > multi-tone FSK modes for robustness. They are much less susceptible to > the effects of ionospheric Doppler and multi-path than other modes. > > They were the only mode types that withstood the 30Hz frequency spread > during the high-latitude tests. That's about as brutal as it gets. > > > Or do you find that with stronger signals, the slow version (50 Hz/50 > > wpm) of MT-63 gets through lightning static and QRM better than even > the > > new MFSK versions designed into the fldigi program? Is there a way to > > simulate this with the software tests? > > I've tried to simulate lightning static by mixing real QRN with > digital mode audio, but it did not work out well. I think a better > approach might be to remove short segments of signal to simulate the > type of heavy static crashes that would obliterate the signal > entirely. It's still missing the AGC capture effect, but it should > tell something about mode recovery after a drop-out. > > Tony, K2MO > > Simulation: High Latitude Disturbed > Path delay: 7ms > Frequency spread: 30Hz > SNR: -3db (weak signal) > Mode Throughput > Contestia 500/16.................100% > CW 20 WPM........................100% > Olivia 500/16....................100% > Olivia 500/8.....................100% > Olivia 500/4......................95% > RTTYM**...........................95% > MFSK31........................... 90% > MFSK16............................75% > RTTY..............................40% > Chip-64...........................10% > Chip-128**....................no copy > DominoEX-4....................no copy > FEC-31........................no copy > Jason Turbo (Fa...............no copy > MT631K........................no copy > PSK10.........................no copy > PSKAM10.......................no copy > PSK31.........................no copy > PSK63.........................no copy > Thor-11.......................no copy > ThrobX-4......................no copy > Feld Hell....................Readable >
