There are down sides to busy-detection: 1. There is no way to know the relative interference temperature threshold for distant co-channel users on HF. SNR at every station is different. A signal that seems in the background at one location, for one mode, may be interference to another mode working at a different SNR or a different mode at another station.
2. What to detect? How sensitive? It is possible to engineer a busy-detector that can be set for a very sensitive threshold, and detect almost any mode or almost any level. That same detector will also falsely show a busy channel most of the time on the HF ham bands. That renders the busy-detector useless for the busy-detector user who wants to have a QSO or send an important message. 3. When does the receiving station with busy-detection know whether the content of such an incoming message is an emergency? A too-sensitive busy detector might prevent such a message from being run in the first place, and the result would not be good. Thus, stations that are on the air specifically with a very likely possible purpose of running emergency traffic should probably not use a busy-detector. It is possible to envision a busy-detector that could be programmed to remotely disengage upon reception of a specific command... but such a system is not readily available at the present time, and the use of it would certainly unnecessarily complicate the sending of an emergency message at a critical time. 4. It may be counter-productive for networks or users to announce what type of busy-detection they use or don't use, because this sort of information can be used nefariously (has been and will be) by individuals on purpose to maliciously interfere or thwart normal operation. 5. We all know that there are many feuds and grudges out there on the air. It seems that certain hams who are most prone to carrying on feuds or grudge-matches may also be the same individuals who clamor most loudly for busy-detectors to be put in place by their "enemy" :) Bonnie KQ6XA
