On Sat, 14 Oct 2017 08:46:13 -0700 (PDT), wrote:

"where are the laws or
regulations which "forbid" them? "

Poor choice of words, there probably is no actual law or regulation, but for
some reason manufacturers omit those frequencies.

There were a few cheap AM/FM/SW receivers on the market in the 1960's
that used 10.7MHz for the first IF frequency. Trying to listen to
anything within about 2 MHz of 10.7MHz was difficult because of
spurious receiver responses from the AM broadcast band. So, there was
a hole in the tuning range from about 9MHz to 12.3MHz. Is that what
you're talking about?

There was also a move during the AM stereo wars (approx 1980 - 1995)
to require AM stereo in all automotive radios. Manufacturers were
worried that there might not be a mass market for AM stereo (which was
proven correct) and that the general public was better served by
having AM stereo shoved down their throat. Similar requirements have
been proposed for satellite radio, and HD FM Radio. To their credit,
the FCC has rejected all such proposals.

Back to the "Quality AM Radio"... To deal with complaints about lousy
mono AM quality, the AMAX certification program was established:
https://en.wikipedia.org/wiki/AMAX
"According to the EIA and National Association of Broadcasters,
tuners and receivers that are qualified to carry the AMAX stereo
certification logo will capture the widest audio frequency
response and highest quality stereo separation of AM stereo
broadcasts that modern technology can offer. In addition,
AMAX tuners and receivers will capture all of the fidelity
transmitted from monaural AM stations. Its audio response
is more than two octaves greater than a standard AM radio."

So, is your favorite AM stereo tuner AMAX certified?
http://pdf.datasheetcatalog.com/datasheet/motorola/MC13122P.pdf
(See Pg 6) Notice that the AMAX spec required a wide/narrow bandwidth
IF switch in order to get decent audio quality. I couldn't find
anything on how or where to get something certified.

Stations still doing AM stereo:
http://meduci.com/stations.html
Better quality AM receiver retrofit (using C-QuAM modulation):
http://meduci.com





--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558