This entire issue simply shows that any protocol which includes
automatic transmission (beaconing, sounding, etc.) or which can
autonomously reply to remote interrogation should be required to
contain and implement a "channel busy" detection circuit that
will inhibit transmission if there is any activity within a
window 1.5 times the "necessary bandwidth" for the modulation
in us. Thus if one were to operate a RTTY responder using 170 Hz
shift 45.45 baud RTTY, the software should be required to inhibit
automatic or autonomous transmission if there was any signal (CW,
PSK31, RTTY, MFSK, etc.) in a 400 Hz Window (using 260 Hz as an
estimate for the "necessary bandwidth"). If one were using PACTOR
III that could "up shift" to a mode that required 2.5 KHz, the
protocol/software should require a "clear" 4 KHz Window.
The protocol should also be required to detect all coherent (non-
noise) modulation methods and not simply its "own kind" to prevent
interference between incompatible methods of modulation. Given
advancements in digital signal processing, such a requirement is
not excessive, nor particularly "costly" in terms of development
resources.
None of the automatic or semi-automatic systems currently in use
have any kind of listen before transmit safeguards for "incompatible"
modulation methods or protocols. With the compression of spectrum
in which digital (non-voice) operation is permitted to US amateurs,
increased protection from the "robots" is vital. While "semi-automatic"
operations have been a problem to human operators since they were
first popularizes in the mid-1980's, fully automatic systems have
not been a significant issue due to the relatively separate spectrum
for "automatic operation." Rapidly increasing levels of narrow
band digital activity due to interest by new HF operators and the
relatively easy access to software like MixW, WinWarbler, MMTTY,
MMVARI. MultiPSK, FLDIGI, etc. coupled with the significant reduction
in non-voice spectrum will make the conflict between human operators
and automatic or autonomous operations critical in the very near
future.
The only way to prevent conflict is to require that automatic and
autonomous systems observe the same "listen before transmit" behavior
expected of human operators and embodied in the rules of the Amateur
Service that states "no licensee 'owns' any frequency."
73,
... Joe, W4TV
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