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HF's position in the electromagnetic spectrum.. High frequency (HF) is the ITU designation [1] for the band of radio waves with frequency between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters (ten to one hundred meters).
30–49.6 MHz: Licensed 2-way land mobile communication, with various sub-bands. [a] 30–88 MHz: Military VHF FM, including SINCGARS; 43–50 MHz: Cordless telephones, 49 MHz FM walkie-talkies and radio controlled toys, and mixed 2-way mobile communication. The FM broadcast band originally operated here (42–50 MHz) before it was moved to 88 ...
Rubber ducky antenna on 446 MHz UHF ... making the antenna shape like the letter 'F' tilted to the right by 90 ... Used as base station antennas for land ...
At lower mediumwave frequencies the ground acts mainly as a good conductor, which AM broadcast (0.5–1.7 MHz) antennas depend on. At frequencies between 3–30 MHz, a large portion of the energy from a horizontally polarized antenna reflects off the ground, with almost total reflection at the grazing angles important for ground wave propagation.
Radio-controlled toys may use portions of unlicensed spectrum in the 27 MHz or 49 MHz bands, but more costly aircraft, boat, or land vehicle models use dedicated radio control frequencies near 72 MHz to avoid interference by unlicensed uses. The 21st century has seen a move to 2.4 GHz spread spectrum RC control systems.
The commercially available B&W AC3-30 and B&W DS1.8-30 antennas [6] vary from the above to cover 3–30 MHz using a 90 foot length with an 18 inch spacing of the wires. The balun is a 16:1 ratio, thereby transforming the 50 Ω (ohm) coax to an 800 Ω feed at the antenna.
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