The mechanics of the broadcasting business are as fascinating to me as the artistry of what goes on the air. In reality, both sides of the equation are art, performance on the air, and the performance of the technicians and equipment that get it on the air.
The good people at KILE-AM/Bellaire were kind enough to provide a tour of their new transmitter site with a six-tower array just completed near Rosharon, Texas. It’s pretty impressive, and when testing is completed and the ink is all dry, the facility will blast into Houston from the south-southwest with a 50,000-watt signal at 1560khz.
This place is literally “over the river and through the woods,” only instead of grandmother’s house, you get to a small transmitter building with six “doghouses” beneath each of the 5/8-wave antenna masts.
Why six towers instead of one?
Because this facility must protect other stations in other parts of the country who also share the 1560-AM frequency. The half-dozen towers are precisely phased so that the radiated signal pattern protects one geographic region, while focusing its energy towards another. So, one tower is effectively negating the power (by a factor of –200 watts), while another tower is blasting in excess of 700,000 watts in the opposite direction. The result is artistry—on a polar graph—and in applied physics.
An interesting detail you will notice is the series of six vertical wires that are suspended parallel to the main tower masts. These are folded dipoles of copper, and are the elements that actually do the heavy-lifting of radiating the signal.
In many of the broadcast facilities around the country, transmitters are meticulously married to networks of copper tubing as their RF is phased and fed to the towers. The coaxial cable that runs the signal between the transmitter and the towers is also copper. But most broadcast towers are constructed of steel, not copper, and their conductive coefficient is significantly less than copper!
At the KILE-AM site, these vertical strands of copper wire are suspended on six sides of each mast, so that there is less loss in the amount of RF produced. Also, because the profile of the dipole is wider than the mast—about eight-feet for KILE—the signal produced is more robust.
KILE-AM is also among the first radio stations in the country to use the new digital HD AM transmitter built by Broadcast Electronics. The unit weighs only 600-pounds, and is so efficient in its conversion of raw electricity to RF, that it runs cool enough to require no ducting from the transmitter cabinet. That efficiency factor is also sufficient that KILE’s digital transmitter will pay for itself in energy cost savings within 36-months...something that should make Al Gore grin.
Thanks to Don Werlinger at Plateau Management, the architect and main contractor for the KILE-AM site, for his tour!