Telamon wrote:
In article ,
"Brenda Ann" wrote:

"D Peter Maus" wrote in message
...
Frank Dresser wrote:

During the time both stations were testing, there were times in which
both
WBBM and WSCR were both running IBOC at the same time and times in which
they were running IBOC alternately. I didn't think about it much at the
time, but I now wonder if they were trying to get both IBOC channels
broadcasting off the same antenna.

Frank Dresser


Not likely. IBOC requires a particularly broad, even spectrum off the
antenna. AM antennae, though broader than comm antennae, are still
frequency specific. Stations of such disparate frequencies would be hard
pressed to meet the flat response required by IBOC on both stations if
combined into a single antenna.


That's not to say it can't be done. But the cost of doing so, and for
experimentation at that, would be far outside BlackRock's capital budget
caps. Not to mention the potential power/pattern repercussions once the CP
was filed. Modification of existing physical plant could open the door to
counter filings, potential protracted legal battles, and even challenges
to existing licenses/operating parameters.

As boneheaded as CBS Radio has been around here in the last 8 months,
even THEY aren't that stupid.

Then, again.........


Large numbers of stations in metro areas are already sharing antenna
systems. Most have done this either in order to decrease the number of
physical plants or to simply save on leasing of or purchase of land for
antenna systems. The towers themselves are only truly narrowband at
resonance. When two (or even more) transmitters share a system, at most one
of them will be at resonance. As far as the matching hardware, it can be
engineered to be as broad as it needs to be.

Antennas can have a broader response by increasing the diameter of the
vertical radiator. This can be done by running at least three wires
around the tower 120 degrees apart with a ring connecting them together
top and bottom minimum. This is much cheaper than constructing a larger
diameter tower. Increasing radiator diameter to broaden the response is
a general rule that can be applied to most antennas.



FM systems share antennae all the time. AM's though, not so much. To
materially change the system, would require a CP which would open the
installation to challenge. This is particularly true of modifying
existing AM's to share common antennnae. Even omni's.