>>>AA6YQ comments below --- In digitalradio@yahoogroups.com, "expeditionradio"<[EMAIL PROTECTED] te:
BACKGROUND There has recently been a lot of bloated theoretical talk about Automatic Busy Detection. My observation is that most of the operators who glorify it and exalt its virtues, have nearly zero experience using it on the air! The same guys who have no experience with it, want to make auto busy detection mandatory for everyone else! >>>No one here has suggested making busy frequency detection mandatory for everyone. What's been suggested is that unattended stations incorporate busy frequency detection in their station control software to keep from QRMing pre-existing QSOs. >snip< DISADVANTAGES Noise can cause false busy channel indication. This prevents use of an otherwise clear channel. Reliable positive and reliable negative discrimination for all signal and noise cases may not be dependable or practical in the ham band environment where any type of signal working at any QSO level of SNR may be transmitted on any frequency. Some of these signals may appear as noise or as too weak to be reliably detected by the human ear, by human eye viewing a waterfall. One clear example is Olivia MFSK with QSOs operating at -15dB SNR. Most humans cannot perceive these extreme weak signal QSOs and the busy detector may not either. >>>A perfect busy frequency detector is not required. Yes, there will be false positives, and these will cause unnecessary delays in message delivery. However, the systems in question are conveying non- critial messages where such delays cause no harm -- except during emergencies, when busy frequency detectors will have been disabled. Yes, there will be situations where a busy detector fails to detect a weak or unrecognized signal. If such a detector is only 80% effective, it would reduce the incidence of QRM from unattended stations by a factor of 5 -- a huge improvement. And as you have often argued, amateurs can improve current performance through innovation. ADJACENT CHANNEL INTERFERENCE Minor adjacent channel interference to a busy-detector-enabled station has the potential to totally prevent or stop communications. This is especially important for emergency traffic, and is also important for reliability on a daily basis. >>>Discussions here have frequently noted that busy frequency detectors should be disabled during emergency conditions. ABUSE OF SYSTEM BY INTENTIONAL INTERFERENCE If automatic busy detection was to be mandatory or obligatory, all stations using it would become very tempting targets for nefarious intentionally interfering operators to abuse the system. >>>Busy frequency detection need only be incorporated in the software that controls unattended stations. Operators using automatic busy detection would be open to potential abuse when it becomes known that any intentional QRM will halt their transmissions. >>>QRMing an unattended automatic station provides little in the way of psychic reward, as no frustrated or angry human response can be provoked. An automatic unattended station could easily outlast any human QRMer. Again, delayed message delivery would not be a significant problem except during emergency conditions, during which time busy frequency detection would be disabled. SUSCEPTABILITY TO INTENTIONAL AMBUSH There is great potential for a nefarious operator to lie in wait on a clear channel, and ambush all others who attempt start a QSO. It would be possible for any nefarious operator to anonymously stop a bonafide QSO already in progress, simply by QRMing the automatic busy detector. >>>see previous response. REMEDY TO INTENTIONAL INTERFERENCE I have personally experienced intentional interference, and fortunately, I was aware of the situation and simply disabled the auto busy detector. >>>Clearly your station is attended, not unattended. Recent discussions of busy frequency detectors here have focused on their incorporation in control software for unattended stations. CONCLUSION In my experience over the past several years, automatic busy detection seems to work best when no one knows you have it enabled! This goes hand-in-hand as an option that can be easily turned on/off at will by the operator. >>>That conclusion makes sense for those attended stations who chose to use a busy frequency detector. We've been discussing busy detection in unattended stations. 73, Dave, AA6YQ . >