SOMETHING THAT THE ARL SAID IN RM-8926 THAT'S NOTEWORTHY

[n9ogl]

"Maia criticizes the inherent infeasibility of information bulletin
and regular scheduled code practice from W1AW to “listen before
transmitting”. The League believes the regularly published, widely
disseminated schedule of the W1AW bulletins and code practice, the
limited duration of each, and the advance warning transmissions are
sufficient to address that concern. However, it should also be noted
that such a capability, even if feasible, is not particularly
practical, given the dynamic propagation characteristics in the
amateur MF and HF bands. For W1AW operator (or any amateur radio
operator) to listen in New England before transmitting is not a
guarantee against interference to other amateur stations. If W1AW is
in the skip zone of a station transmitting, W1AW will not hear the
transmitted signal. That does not mean, however, that the intended
receiving station is in the skip zone of W1AW. Nor are electronic
circuits to determine frequency activity successful at HF. One reason
is the noise level varies constantly by both types and amplitude. It
is difficult, therefore, to discern signal from noise in these bands
by use of a squelch circuit. The problem is further complicated by the
fact that HF frequencies are not channelized, and receiver bandwidths
vary from amateur station to amateur station. These matters, however,
are no more a problem for one-way information bulletins from W1AW then
they are for any amateur station engaged in two-way communication, and
do not offer any support for the allegation that HF bulletins, voice,
cw, or data, are somehow improper on the HF bands."

ARRL comments on RM-8626 footnote #4