Packet radio gets by with a simple carrier detect, PACTOR can only detect other PACTOR stations, and from what I can tell, ALE has no busy detection at all.
Several years ago I took a serious look at automated busy detection, and always ran across the same stone wall: A more sophisticated busy detect that can usually tell the difference between noise and a human activity like speech or digital transmissions is possible - BUT - only after the software has a fairly long audio sample to work with, and can look back upon that sample. It can't do this instantly, or even very quickly unless you have a supercomputer to work with. If it listens to a long sample and a new signal comes in toward the end of that sample, that new signal may or may not end up being identified. This is a terrible thing to have to report, but Packet's carrier detect is the most effective and sophisticated automatic signal detection scheme we currently have at our disposal. - It detects more kinds of activity *right then* than anything else that hams are currently using. There are lots of signals that carrier detect will not detect - but it is still the best thing out there, that can automatically detect and act in ( more or less ) real-time. The human ear works better, detecting signal intelligence and differentiating it from noise far better than any automated detection system. Period. Better still is the human eye, looking at a properly set up waterfall display that will show you recognizable patterns in the waterfall image that you may not be able to register just by listening. One thing to ponder is why carrier detect, developed over twenty-five years ago is not utilized by PACTOR or ALE, both allegedly more advanced than Packet. My feeling on this is that if they cannot detect signals as well as Packet does, then which mode is more advanced, more suitible for use on the ham bands? That is really an unfair question in the case of PACTOR III and ALE, niether one of which was designed or ever intended for use within shared amateur radio spectrum, in the first place. It is not the square peg's fault that it will not fit in the round hole. In the end, if we are not operating an automated station, then a waterfall display in combination with speaker audio is the most effective and useful busy detection system we have at our disposal, and this will almost certainly continue to be the case for a very long time. For real-time automated busy detection, carrier detect is highly likely to be the best thing at our disposal - again for a very long time. The Reed-Soloman ID system is a great step ahead for digital operation. It is not really useful as a real-time busy-detect, but it does give us a first step on something that may eventually take us there. As standards and hardware evolve over the years, we may eventually embed information into our data streams that can be instantly recognized as 'busy' by our software. - It may even approach the speed of carrier detect, and work with all modes. But don't hold your breath, it's not right around the corner. 73 DE Charles Brabham, N5PVL Prefer to use radio for your amateur radio communications? - Stop by at HamRadioNet.Org ! http://www.hamradionet.org
