--- In digitalradio@yahoogroups.com, John Becker <[EMAIL PROTECTED]> wrote: > I have a couple of books on RTTY dating back to the 1960's. They talk > about using TU's that can decode with only the mark or only the space > signal. This seems pretty straightforward, since the mark and space > together provide 100% redundancy. I haven't figured out how to do that > with what I'm running, and on weaker signals I'm finding a tuning error > of only 10Hz can make the difference between copy and no copy. >
Decoding with mark only or space only was something that seemed like a good idea at the time to get improvement over the true-FM limiter-discriminator design. It didn't turn out to be all that useful, because when signals are so bad that they fall below the threshold for FM then they are so bad that you don't copy much anyway. I honestly don't know much about the modern sound card DSP decoders, but I imagine they detect the mark and space separately and then combine the results. > What do I need to do better? Are there any good recent books on RTTY? I don't expect to see any new books on RTTY, because it is a technology that is pretty much as good as it is going to get. Better performance these days comes from the newer sound card modes. RTTY is mostly used now for contests and DX, and the reason I think is that it has very fast turnaround, so you can make contacts as quickly as possible. You don't care that much about accuracy so long as what you see looks like what you want to see, hi. Also back when RTTY was the only keyboard mode we had most hams were running quite a bit more power than is the norm today. 500 watts was pretty standard for RTTY back then. For general rag chewing today most everybody has gone to PSK-31. There is some tweaking you can do with RTTY things like the MMTTY engine, which has several different filtering and detecting options. Maybe somebody will speak up about how to use them to best advantage. You might benefit by putting on the whole MMTTY program and using it to learn how to take best advantage of the displays and features. As a 50+ year user of RTTY I hate to sound so negative about it; but the fact is that technology has moved on. Jim W6JVE
