On 10/16/09 13:03 , SMS wrote:
D. Peter Maus wrote:

Yeah, actually, it does. The digital system is virtually a separate
system, requiring separate transmitters and towers.

No, actually it doesn't. Or at least it usually doesn't require a new
transmitter.

As long as the existing transmitter has an extra 10% of power headroom
to overcome combiner losses, you can do high-level combining and you do
not need a new transmitter (or tower).

If you have to buy a new transmitter then of course the cost goes way up
but you still don't need a new tower.


That assumes the existing array is broadband enough. That's an
issue in directionals and some older omni's. Some DA's can be
broadbanded to accomodate the two channel extra bandwidth.
Some...not so much. Even broadbanding an existing array can run into
money. At the station in Iowa, we tried for the entire time I was
there to broadband the antenna so we had fewer issues at night some
of which were severe, presenting highly irregular loads to the
transmitters. There were audio artifacts that became quite
objectionable. Spent bags of money on it. And never did get it where
we wanted it to be.

Eventually, everything was replaced with newly redesigned and
engineered hardware. Including north tower which was the center of
our broadbanding problems.

And that was a single channel's bandwidth. For IBOC, they'd
have to tear out everything from the program line terminal to the
toplights.





They are not separate systems, either virtually or in reality. No
stations at all would be broadcasting HD if it required separate
transmitters and towers.


Many of the stations around here installed them as separate systems.



John can answer the question as to how many stations have transmitters
with that 10% of headroom, but apparently many do.

The question is IF the existing transmitter has that kind of
headroom. Often, especially in the case of some lower margin
stations, this is not the case. Even in the cases of big markets,
new hardware is often installed. WGN put in new transmitters for the
implementation of IBOC.