wrote:
As has been discussed, HD Radio is not currently authorized on AM
stations at night, ("night is *not* defined as 6 AM to 6 PM, but rather
varies with a station's geographic location and the time of year)
though a serious lobbying effort is on to change this. Hence, at this
point it does not seriously impact DX opportunities, since most
long-range reception is a nighttime phenomenon (when the IBOC signals
are off).

From FCC Public Notice DA-03-831:
(http://www.fcc.gov/fcc-bin/audio/DA-03-831A1.pdf)

"Until further notice, AM stations must restrict IBOC operation to
daytime hours. An AM station with authority to operate between 6 a.m.
and local sunrise (pre-sunrise hours) and between local sunset and 6
p.m. (post-sunset hours) may operate its hybrid IBOC system during those
periods. "

As I read that, AM stations that are authorized to operate in analog
between the hours of 6am and 6pm are also authorized to operate IBOC
during those hours. Admittedly those two sentences could have been
worded a lot better!

That is indeed a different definition of "night" than the one the FCC
uses for determining whether a station should be on nighttime power
and/or antenna pattern. Mike's KDIS is required to reduce power from
50kw to 20kw at night, and that change is required to take place at
4:45pm. (for the next two days; it slips to 5pm on the 1st of January)
But as I read it, they can leave the IBOC on - on the lower power and
night directional pattern - until 6:00.

Again, my sense is that broadcasters are thinking that the analog
technology that served us well in the 20th Century has run its course,
and that to remain a viable medium a transition to digital *must* take
place. The trouble is that there are (probably) a half-billion analog
receivers in the USA alone capable of receiving analog AM / FM, and
these can't be abandoned overnight. The Station's around the country
are now in the first phase of implementing digital radio, in the form
of IBOC / HD Radio. And my bet is that it's *not* going to go away.

We are finding in TV just how slowly old receivers are being dropped.
In TV we have the advantage of cable and satellite operators doing the
downconversion for us in 85% of households - and the fact that a given
household has a relatively small number of TV receivers. Also, by using
an "in-band separate channel" conversion scheme, the new digital TV
signals result in little or no interference to existing analog service.
Even so it appears the transition will take more than ten years.

Radio doesn't have most of those advantages. Nobody will be
downconverting HD to analog for old receivers. Most households have
handfuls of radios - far more than they have TVs. For the millions of
us in outer suburbs (and the millions in lightly-populated and rural
areas), the interference will not be negligible. Especially on AM.

FM IBOC is certainly an upgrade for those who listen to mainstream
stations *and* live (and commute) in the core of the market. It is
likely to be a major unpleasant surprise for those who live in outer
suburbs and outlying towns.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com