[BC] Digital coverage

[DANA PUOPOLO]

FM IBOC works okay in the lab and out in the desert, where all stations are
fully spaced. It's a disaster on the east and west coasts where most stations
are short spaced to others and a lot of grandfathered superpower FM stations
are. A good example: I was CE of the 103.1 class A licensed to Santa Monica,
CA. Santa Barbara (about 75 air miles away) has a superpower 103.3 (105 kW at
about a mile AAT). Its 54 Dbu contour completely covered Santa Monica and
actually extends PAST the 103.1's transmitter site! The day that 103.3 lights
up IBOC, the coverage of the 103.1 will shrink to about 20% of what it is now
(and I'm talking about PROTECTED coverage, not "extra" coverage).  Can you
understand? It will be impossible for the 103.1 to be heard within most of its
city of license any more! How the FCC can allow this is beyond me!

-D


------ Original Message ------
Received: Fri, 23 Dec 2005 01:43:01 PM PST
From: "gRAdy Moates" <lists at loudandclean.com>
To: broadcast at radiolists.net
Subject: [BC] Digital coverage


>This probably doesn't bode too well for a lot of class A FMs out in 
>"B" country, particularly along the east coast.

    My feelings, exactly.  Ibiquity HD seems to work OK with full B's 
and C's, simly because the allocation system we use doesn't allow as 
many, small first- and second-adjacent interloper signals that are 
close-in to the primary service area of a station.  The smaller the 
footprint of a station, the more 'edge problems' it will have.

>I wonder if the situation would improve any when (if) we get out of 
>the hybrid and into the full-digital mode.

    Performance in full digital is the real "pig in a poke" about HD 
as developed by Ibiquity.  As I read their white papers, when we (the 
industry) turn the analog off, the _existing_ IBAC carriers get 
turned up, and we get to add additional IBOC carriers where the 
analog was, but at a lower level than the IBAC carrier groups.

    This means that the receivers must be able to receive 
'interleaved' carrier groups, where a lower-first-adjacent interferer 
will have it's high-level upper IBAC carrier group within the area 
where the desired station's low-level IBOC carriers will be.

    Ibiquity's drawing of this is excerpted here:
                www.loudandclean.com/digital.jpg

    This may, or may not work well in the real world, and no amount 
of lab testing or pre-deployment testing with two or three stations 
can come close to telling us what it will be like when we flip the 
big switch and convert the whole industry to digital-only on that 
great day in the future.

    But We Can All Hope For The Best.

Grady




_______________________________________________
This is the BROADCAST mailing list
To send to the list, email: broadcast at radiolists.net
For sub changes, archives and info on this other lists:
http://www.radiolists.net/