right now, HD is only transmitting during day time hours.  One of the
problems with HD is what happens to the lock on the signal when it begins
fading in and out as the signals fade at night.  I don't believe that
problem as been solved or even discussed much what they are going to do
about the problem.  It may be that digital radio stays sun up to sun down
and the standard A M broadcast signals will be used at night.  I haven't
heard much about it lately.  Also, as you have noticed most likely, the
digital signals are smaller in band width so they can have signals in
between the standard A M broadcast siggals.  Plus, with HD signals, they can
transmit data to your receiver about who is on the air at that moment, who
the guest is, the name of the song and who is playing it, the CD title, and
much more.  It is all displayed on your receiver.

Phil.