Sample Application: Multiband Shortwave Transmitter
One of the longest lasting applications for dedicated antenna tuners is in high power shortwave broadcasting transmitters (50 kW+), where antenna tuning is a must due to frequent waveband changes. Every multiband shortwave transmitter sold since the 1950s has had one as part of its design. Most notably, some designs used a miniature railroad system to swap out capacitors as the longer wavelengths demanded larger capacitors.
Most antennas used in high power shortwave broadcasting are HRS type antennas, where the radiating elements are of a fixed length and the resonance of the antenna is optimized for only one or two bands. It typically takes about one minute for a modern antenna tuning unit to adapt to a frequency change in a broadcast band, and about two minutes to adapt to a change of two bands plus or minus. Some wideband shortwave broadcasting antennas don't need antenna tuning units; namely the Log Periodic type.
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