Tom,

   There is no manual switch or menu setting to change to or 
from HD Radio.

When you tune to a station that is transmitting HD, the 
radio will automatically switch to the first HD stream, *if 
the analogue signal is clean. HD doesn't like noise or 
flutter.

This change can take as much as 30 seconds to occur. 
Depending on the setup at the transmitter, you will either 
hear only the change in the sound of the signal, or what 
sounds like a major hiccup in the station audio for a few 
seconds. That is, sometimes the delay between the analog and 
HD stream is such that the change will sound as though 
somebody at the station hit the "back up by 10 seconds" 
button.

When the radio goes into HD mode, it automatically lands on 
the "HD1" stream. By mandate from the FCC, this stream is 
always the same programming that is heard on the traditional 
analogue channel. Some stations only broadcast this single 
HD stream.

If a station is broadcasting two or more HD streams, a 
single press of the up button will move you to the second or 
third stream just as it moves to the next station in the 
analogue mode. The down button will return you to the 
previous stream.

Once you tune past the last stream of a given station, the 
radio automatically goes back into analogue mode to find the 
next station, and the process begins again.


Most stations are broadcasting two streams, and some have 
three. While there is no rule against it, I do not know of 
any station currently broadcasting more than 3 streams.

The greater the number of streams, the more narrow the 
frequency responce of each one. Thus, the HD3 streams I have 
encountered tend to be mostly talk or foreign language 
channels, and not be in stereo.

In HD mode, the visual display will usually show the call 
letters of the station, followed by HD, HD2, etc.

Most receivers have buttons which will cause the display to 
also display song titles, other program information, etc. 
There is a major experiment in the works to use that display 
mode to communicate weather warnings and other disaster 
information to people who are deaf. Right now, that 
experiment is only along the gulf coast, and includes one of 
the stations in the network that I work for here in 
Mississippi.

Hope this wasn't more than you really wanted to know.