>>>AA6YQ comments below
From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Steve Hajducek >snip< 2. With respect to Remote User to Automatic Station communications, the human operator initiates the communications and its all up to them to decide the coast is clear to do so or not and if they need to stop because they screwed up and did not listen long enough ( how long is long enough? >>>The hidden transmitter effect means that the remote initiator cannot reliably ensure that the coast is clear. >>>If we're on the telephone from California and say "14180 is clear here, give me a call there", can you transmit on 14180 from your QTH on the east coast without first listening to see if 14180 is clear there? Of course not; doing so might QRM a station in Florida that you hear 59 but I don't hear at all. Now consider your station to be an unattended server and my station in California to be the remote initiator. Your unattended server will QRM the station in Florida. be it human operator or computer software there is not now and never will be any perfect means of busy detection in my opinion) to detect that the frequency was indeed in use due either propagation or just plain long pauses between transmissions of the 3rd party stations. >>>"Perfect" is unnecessary. It is clearly possible to build busy frequency detectors that are at least 80% effect, since such a busy detector was demonstrated years ago. Applying such an imperfect busy detector to unattended stations would reduce their QRM by a factor of 5. >>>This "it's impossible to build a perfect busy detector" argument reminds me of Xeno's paradox, in which he proves that all motion is impossible. In closing, you and everyone else on this frequency busy detection quest just don't seem to grasp the realities the shared aspects of the Amateur Radio bands and tolerance for co-frequency levels of interference and just what it is that you are proposing with your frequency busy detection dream. >>>To what "realities" are you referring? Amateur radio bands are certainly shared, but that gives no station the right to QRM existing signals. Also you seem to think the issue is with Automatic Stations, when in fact it is really with Human operated stations. If there is going to be frequency busy detection in digital mode communications software ( and hardware where all that is not so equipped would need to be banned from use to make your dream a reality) than it needs to be in the Remote User's software to second guess the human factor at all times and not in the Automatic Station side as its the human operator that initiates the communications, for any Automatic Station Forwarding between like stations then and only then would frequency busy detection apply to the Automated Station initiating the connection. >>> What are you talking about? The issue is preventing an unattended station from transmitting on a frequency that is already in use. Also, to be as complete and concise as possible, such frequency busy detection needs to be applied to all known and legal for use digital modes around the world and not just detection of RF energy period ( else your station may never go into TX ). Doing so would force all human users to be courteous and standby when any real digital mode signal that is within their passband from any source, which will force the use of narrower filters for given modes or cause stations to yield to wider band mode operations and narrow bandwidth modes operations will have to steer clear of wider mode operations. Then, depending on the timing of who transmits first and what the forced upon you timing constraints of the algorithms used end up being, you just sit and wait for an opportunity to transmit, you may get out a CQ or other call but then your system detects another signal and puts you into a holding pattern again, should it be just any signal detected at any time? Should be only when both sides of signal exchange are heard so that your station isn't just making you wait due to another station CQing etc., if not full QSO detection in the given mode of operation then what about that "hidden transmitter" effect?. Oh, I can see it now, a lot more listening for everyone, the early bird gets the frequency for the QSO, gee what a dreamy situation, but when an ECOM event comes about, will they ever get a chance to send that health and welfare traffic in a timely manor or at all? Hopefully some of this has assisted you in seeing more of the complexity and down sides of this busy frequency detection dream Rick. >>>Attended stations already have effective (though imperfect) busy frequency detectors: their operators. The problem is unattended stations, which do not. >>>As has been suggested many times, during emergency conditions an unattended station would disable its busy frequency detector. 73, Dave, AA6YQ
