>If I gave you some parameters of a waveform, what would you use to base >your measurement of baud rate?
I would look at the data, and see how it is modulated into an analog waveform. For FSK we know that a 1 produces one symbol, and a 0 another symbol. MFSK16 the symbols represent 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 4 bits per symbol. For MT63 there are 64 bits per symbol. All 64 PSK signals combine to produce 1 waveform, just like a two tone, 3, tone or 4 tone test produce a waveform. The complex voice signal produces a waveform. PACTOR III uses the same logic...Up to 18 tones are used, spaced at 120 HZ. I can take a picture of the MT63 waveform and put it on the Internet if you like. >Are you saying that the reason that packet performs so poorly is due the >fact that it has no convolutional coding or interleaving? Yes, I would say that it is not as well suited for HF operation as other modes. >All along what Walt and I have pointed out was that ISI becomes >intolerable with difficult propagation conditions (e.g., doppler, polar >flutter, etc.) with short symbol lengths. The longest symbol length >possible for 300 baud is 1000/baud or 1000/300 = 3.33 ms. That is a very >short pulse for HF. That is why Pactor chose 100 baud = 10 ms minimum >pulse length (assuming they are continuous with no gaps). That 10 ms >length is about the right amount, particularly with some DSP enhancements. You can overcome those issues by interleaving, convolutional encoding, redundancy, and spreading the signal. I would say the real reason why 100 baud may be the limiting for PACTOR III is not only the RF medium, but the radios that are using it. Amateur gear I am sure is not designed for low group delay distortion. >If the baud rate of a waveform was 2400 as Steve has often mentioned, >wouldn't the longest possible symbol length be about 0.42 ms? If this >really can work on HF, it is completely contrary to what I have learned >over the past few decades, particularly when Pactor was first on the >scene. Even with extensive DSP, can you overcome that large of an ISI >issue? Apparently you can, however we will never know unless we join MARS, or get the arcane 300 baud limit lifted. 73, Mark N5RFX 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 <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> 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/
