[BC] Digital coverage

[Phil Alexander]

On 24 Dec 2005 at 22:22, DANA PUOPOLO wrote:

> 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!

Dana,

Do the math, because that is how they allow it.

KVYB 105. kW ERP, 905. meters HAAT 
(2969 feet HAAT - a little over 1/2 mile)

KDLD 3.7 kW ERP, 82. meters HAAT

KDLD appears to be a short spaced, grandfathered Class A with a 
granfathered superpower Class C (KVYB) first adjacent.

The dist. and azi. from KDLD to KVYB is: 155.98 km/96.92 mi @ 291.80°

The areas where the 60 dBu of KVYB overlaps the 60 dBu of KDLD 
would probably interfere with KDLD, HOWEVER:

The 50/10 60 dBu of KVYB lies 128.513 km from the Tx site
The 50/50 60 dBu of KDLD lies 23.095 km from the Tx site
The sites are 156 km apart; there is no 60/60 overlap.

Thus, within its 60 dBu primary coverage area, KDLD should have 
greater than a 20 dB D/U ratio vs. the IBOC subcarriers of KVYB.

If interference is found within the 60 dBu contour of KDLD, their
first recourse would be to the FCC who *might* order a reduction of
KYVB's IBOC subcarriers to a level commensurate with a standard
Class C allocation, or about 4.5 dB below the standard injection
level increasing the average D/U ratio to about 25 dB in the worst
case.

Compared with some of the AM IBOC problems this is insignificant.
KDLD will lose some fringe coverage to the northwest, but I doubt 
they will see an effect in their COL. I'm seeing worse situations 
here in the Midwest between B's and A's, as well as A's and A's.

I'm no great fan of IBOC because it appears we will have terrible
problems with some situations in the AM band. However, picking
the situation above as an example falls short of the "How CAN
they do this," mark. 

The real problem is allocation of A's to "cities" that can't
adequately support a radio station in today's market although
some Newton Minnow idealist of the '60's put an allocation there.
Now, many of those Class A's are trying to survive by rimshot 
into a nearby major market where they have a 54 dBu signal or 
less. If the FCC would drop the COL pretense and use engineering 
rather than mileage separations, most of these problems would be 
resolved over 10 or 15 years, especially if there were a financial
incentive for cleaning up the band, but that will never happen.
The government can't collect fees from a station that is sold to
go dark.


Phil Alexander, CSRE, AMD
Broadcast Engineering Services and Technology 
(a Div. of Advanced Parts Corporation) 
Ph. (317) 335-2065   FAX (317) 335-9037





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