If you’re in the commercial AM radio business, you want to send your signal as far and wide as possible. More listeners means you can make more ad revenue, after all. [Jeff Geerling] recently visited a tower site for WSDZ-AM, which uses a full eight towers to broadcast its 20kW AM signal. To do that, it needs a phasor to keep everything in tune. Or, uh… phase.
The phasor uses a bunch of variable inductors and capacitors to manage the phase of the signal fed to each tower. Basically, by varying the phase of the AM signal going to each of the 8 transmitter towers, it’s possible to tune the directionality of the tower array. This allows the station to ensure it’s only broadcasting to the area it’s legally licensed to do so.
The tower array is also configured to broadcast slightly differently during the day and at night to account for the differences in propagation that occur. A certain subset of the 8 towers are used for the day propagation pattern, while a different subset is used to shape the pattern for the night shift. AM signals can go far farther at night, so it’s important for stations to vary their output to avoid swamping neighbouring stations when the sun goes down.
[Jeff’s] video is a great tour of a working AM broadcast transmitter. If you’ve ever wondered about the hardware running your local commercial station, this is the insight you’re looking for. AM radio may be old-school, but it continues to fascinate us to this day. Video after the break.
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