 |
The CGC Communicator Newsletter Web Posting |
|
With respect to this story published in CGC #735....
******************************************************************
CLEAR CHANNEL CE COMMENTS ON AM IBOC POWER LEVEL
The following letter, reportedly from Steve Davis, Chief
Engineer, Clear Channel Radio, is posted on the radiolists.net
website to resolve a controversy associated with AM IBOC sideband
power levels. While it is one thing to quote the power of an
individual carrier within an IBOC sideband, it is another to
quote the aggregate power of all the IBOC carriers.
For a 50 kW AM station, the aggregate IBOC power amounts
to 2.4 kW according to the Davis letter, not 500 watts as had
apparently been claimed in an earlier posting.
http://tinyurl.com/q6kn7
******************************************************************
....author Barry McLarnon sheds further light on the AM HD Radio interference concern in his latter dated May 1, 2006:
If you're wondering what caused Steve Davis to see the light, see
http://lists.radiolists.net/pipermail/broadcast/2006-March/029403.html
Note that his posting that you provided the link to, while correcting his
error about AM IBOC power levels, contains other misinformation regarding
the nature of the digital modulation and claimed protection to adjacent
channel stations.
For the rest of the story, see:
http://lists.radiolists.net/pipermail/broadcast/2006-April/030053.html
His response, with some further corrections:
http://lists.radiolists.net/pipermail/broadcast/2006-April/030305.html
The key point, of course, is that the signal processing "trick" used in
the AM IBOC signal is designed to keep digital noise out of analog receivers
tuned to the host IBOC station - it does absolutely nothing to keep the
noise out of receivers tuned to adjacent channels. And, in the real
world, it often fails even at its intended purpose, since there are a
number of factors that can disturb the delicate orthogonal relationship
between the analog signal and the digital carriers - DA pattern bandwidth
problems, for one.
I'm sure Steve's heart is in the right place, but despite all the effort
and positive spin he and others put into it, the fundamental flaws in this system simply cannot be fixed.
Barry McLarnon, VE3JF, Ottawa, ON, Canada
Posted by Steve
Blodgett
Earthsignals.com