KOOL Listener Lauren said:Thank you, David. So, while we're on this topic, what's the goal with AM directional testing? Is the signal's distance increasing with this testing, or are the tests mapping out how far the signal goes?
When it comes to antennas, signals, and those sort of things, I know absolutely nada!
With a couple of exceptions, most of the thousands of AM directional stations are directional to protect other stations from interference. The way this is achived is by using multiple towers and feeding each with signal in a way so that the radiation is not cirucular but "directed" away from the protected stations. In general, older stations are given protection from newer ones, and stations often have to protect signals on adjacent channels, too.
The basic system, meaning the spacing of the towers from each other and the equipment that sends precise amounts of power to each tower in a determined phase relationship is predesigned. Once installed, it is pure real world. Since the conductivity of the soil, electrical lines, buildings, hills, all affect the radiation, there is lots of adjustment to make the operation conform with the licenced values.
The gear at the transmitter is adjusted, measurements of signal at predetermined distances and compass bearings are made, and more adjustments are made till the system radiates as required by the FCC. In a few cases, theoretical designs could never be made to work, and the system had to drop power or be redesigned.