Hi, Everybody,

Over the past couple of years several AM broadcast stations in the L.A. area
have begun transmitting the new "HD Radio" signal. A "high quality" digital
signal is superimposed on the standard AM signal and so the station can be
received with either type of receiver. I believe there are about ten
stations now doing this here in L.A. and probably everywhere else in the
country.

Have you tried this?: Tune in a local HD AM broadcast station on your
general coverage receiver in SSB mode, either USB or LSB. When you zero beat
the station you will hear a loud rushing noise floor behind the program
audio. This morning, Rush Limbaugh and Dan Patrick sounded like they were
each doing their shows from in front of Niagara Falls.

Even in AM mode, as you approach the station from either direction you'll
hear a hideous broadband noise until you get onto channel center. It's
really annoying and bad for AM DXing because of the interference (in the
form of increased noise floor) these local stations cause to the weak DX
ones on either side of them.

Al W6LX

Info isn't plentiful on this, but these may be of interest:

http://www.ibiquity.com/

http://users.tns.net/~bb/hdrsn.htm

Roger K6XQ