>>>AA6YQ comments below
--- In digitalradio@yahoogroups.com, "expeditionradio"
<[EMAIL PROTECTED]> wrote:
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.
>>>This is easily resolved. If *any* intelligence is detected, QSY.
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.
>>>This is one of those "we can't make it perfect, so let's not do it
at all" arguments. SCAMP demonstrated several years ago that busy
detection is practical, but the advocates of unattended operation
have chosen to spend their time politicking rather than further
developing this technology into something that would allow them to
politely and effectively share spectrum with the rest of the amateur
community.
3. When does the receiving station with busy-detection know whether
the content of such an incoming message is an emergency?
>>>Busy detectors prevent messages from being transmitted, not from
being received.
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.
>>>A unattended station designed to carry emergency traffic could
easily be designed to reliably decode an "emergency enabled" message
and disable its busy detector from impeding the transmission of
outgoing messages until an "emergency disabled" message is received.
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.
>>>During emergencies, busy detection would be disabled. During non-
emergencies, even the most pathological lid would quickly tire of
QRMing an unattended station that never reacts with frustration or
anger, patiently waiting to pass its messages until the frequency
clears.
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" :)
>>>If unattended stations adopted busy detectors and stopped QRMing
ongoing QSOs, the level of frustration among digital mode operators
would drop. As pointed out above, intentionally QRMing an unattended
station is a most unsatisfying pastime.
73,
Dave, AA6YQ
