This Ruby gem calculates the optimal length for a half-wave wire antenna for use in shortwave and amateur radio operations.
Download and install the 'shortwave_antenna_calculator' gem.
And then execute this command in a terminal shell:
$ launch
Very simple - when prompted, just enter the frequency in MHz, using decimal notation. The result will be the optimum antenna length for your frequency, expressed in feet.
The program currently only accepts frequencies between 1.8 MHz and 30 MHz, which covers most of the high-frequency portion of the radio spectrum. Future enhancements are in the works to expand the covered frequency range to include the VHF band.
Source: The ARRL Handbook for Radio Communications, 84th Edition, American Radio Relay League, 2007
Examples:
(1) An amateur (ham) radio operator wants to construct a half-wave wire antenna (dipole) for the 20-meter band, centered on a frequency of 14,280,000 Hz. This frequency is equivalent to 14.280 MHz in decimal notation. Enter 14.280 when prompted by the program.
(2) A shortwave listener (SWL) is interested in setting up a wire antenna that is optimized for listening to a low-power shortwave station on the opposite side of the globe on 8652 kilohertz. Expressed in megahertz, enter 8.652 when prompted.
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