When I first started at the now-extinct Meyer Broadcasting in 1990, the employee handbook boasted the KFYR AM 550 tower as the tallest free-standing radio at the time it was built. I don’t know how it stacks up now, but it’s a pretty tall structure. The “stick” towers you see held up by guy-wires are much much taller, but that’s because they have lots of additional support. These beasties here are built on top of big insulators and have no wires helping them stay upright.

AM radio towers are different than others in that the tower is the antenna. An FM or television “stick” is simply a tower with an antenna at the top of it. So you don’t want to be anywhere near an AM tower while the transmitter is operating!

The little tower is an interesting feature. AM radio signals travel using “ground wave” propagation during the day, but at night the sky’s ionosphere changes and reflects AM radio waves back to earth. That means an AM station can be heard a LONG ways away. So what if there are two 550 AM stations? There are actually a lot more than two, but two high-power 550’s near each other’s range of operation could run into problems if their signal areas suddenly grew at night and overlapped each other. That’s why many stations, including KFYR, “go directional” around sunset each night.

The little tower is energized and “pulls” the signal toward Bismarck (away from Canada, rather) so that it does not cause interference with the other 550s north and east of us. By controlling the power to each transmitter, the engineers can “shape” the signal area in such a way as to avoid interference. Pretty cool, huh?

These days, the transition back to “non-directional” happens during the PH Phactor in the mornings. As sunrise comes earlier, that’ll start to get done before Phil takes the board. But you’ll know the switch is happening when you hear a burp of static for a second or two, then the signal returns to normal.