Hello Rick, >Do you think that it would be possible for some hams to develop >something similar, or better yet, follow the MIL-STD specifications so >that we have future continued interoperability? I think PCALE and MARSAle have also integered the 110A mode. I hope thay are interoperable with RFSM (?) for at least a common part. However as far as I know the 110A specifications just describe the way to send messages. It is not described: * the way to do the equalizer (everyone does the best possible) on the receiver part, * the protocol to work in an ARQ mode way.
>Do you have any idea why they use such a high baud rate all the time, >even when sending the more robust slow speed data and use multiple >repetitions? They use the same modulation: 2400 bauds 8ary PSK all the time, so to recognize any change of speed or interleaving length (given in the preamble). Of course you cannot have very good minimum S/N even at 75 bauds with such a high speed (minimum S/N must be >=0 and depends on the bit rate selection), but reversely you can go up to a bit rate of 4800 bits/sec... I suppose that the implicite specifications are a very good throughput with a not too bad S/N. >While the MIL-STD does provide for multi-tone as well as single tone, it >appears that most development has been for the single tone, therefore >there must be a logical reason for this. The single tone is the basic choice, multitones schemes are only options. >I still don't comprehend why this concept is so good compared with >multi-tone modems. In fact, some of the information I have been able to >find, does have the multi-tone slower baud rate perform better than >single tone high baud rate in some cases. But often it is supposedly >very close. For the same mean HF power, I think the multi-tone must be better because the speed is low and you don't need an equalizer. The equalizer cannot have a perfect performance because the ionospheric transfer function can be identified only approximatively and the function is not strictly stationary between two known data transmissions. >Is the reduced crest factor the main advantage for the single tone? Is it >around 1.0? I don't see anything about some windowing in the 110A specifications so the crest factor is 1, when, for the multitone, it is very bad (around 0.1or 0.2 depending on the number of tones). >What would happen if a slower baud rate were used with a single tone modem, >instead of the high baud rate? (Of course it would not be MIL-STD anymore). The idea would be good but of course we will have an exchange between bit rate and minimum S/N qualities: the minimum S/N would be better and the bit rate smaller. But I think 2 tones would be also good: it would permit to double the bit rate, each tone being a channel for the convolutionnal coding. The crest factor factor would be 0.5 without windowing and around 0.35 with a windowing. If you would set your transceiver to the maximum (100 watts) you would supply 35 watts to the antenna, which is sufficient for a continuous working. HW? 73 Patrick ----- Original Message ----- From: Rick W. To: digitalradio@yahoogroups.com Sent: Saturday, June 07, 2008 3:42 AM Subject: Re: [digitalradio] ALE 400 auto speed change Hi Patrick, As you know the Russian RFSM developers have adapted MIL-STD-188-110A (maybe even more advanced than that?) as a software modem. It apparently took a large programming effort to do this. Do you think that it would be possible for some hams to develop something similar, or better yet, follow the MIL-STD specifications so that we have future continued interoperability? Do you have any idea why they use such a high baud rate all the time, even when sending the more robust slow speed data and use multiple repetitions? While the MIL-STD does provide for multi-tone as well as single tone, it appears that most development has been for the single tone, therefore there must be a logical reason for this. I still don't comprehend why this concept is so good compared with multi-tone modems. In fact, some of the information I have been able to find, does have the multi-tone slower baud rate perform better than single tone high baud rate in some cases. But often it is supposedly very close. Is the reduced crest factor the main advantage for the single tone? Is it around 1.0? What would happen if a slower baud rate were used with a single tone modem, instead of the high baud rate? (Of course it would not be MIL-STD anymore). 73, Rick, KV9U Patrick Lindecker wrote: > Hello Rick, > > >Note that the bandwidth is perhaps five times wider for 2 1/2 times > more throughput. > Normally it would be possible to have a 2000 Hz ALE at 250 bauds > instead of 125 bauds. For, I suppose, a reason of frequency diversity, > the shift between two adjacent tones in ALE is twice > the baudrate (when the minimum between two adjacent tones would be a > shift in Hz equal to the baudrate). > However for big transfer speeds, there are the choice between several > solutions, for example: > * something close to the 110A solution: one carrier modulated at 2400 > bauds 8ary PSK and different configurations (but with a necessary > equalizer and some regular known data to supply the equalizer), > * or many carriers modulated in BPSK (or QPSK) as with MT63, but a > weak crest factor and no need for an equalizer. > > 73 > Patrick > >
