>>>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
.
>
