highfrequency

High frequency is a term used to describe the upper part of a spectrum within a given domain. In radio communications it refers to the high-frequency (HF) band, roughly 3 to 30 MHz. In other fields, “high frequency” indicates signals or activities at the upper end of the relevant range. The exact boundaries are context-dependent.

HF radio enables long-range contact through ionospheric reflection. Waves at these frequencies can be refracted by the ionosphere, allowing beyond-line-of-sight communication. Propagation depends on time of day, season, and solar activity; the Maximum Usable Frequency and skip distance govern feasibility. Daytime D-layer absorption reduces range; nighttime conditions often improve it. Common modes include voice, Morse code, and digital protocols.

Applications include international broadcasting, amateur radio, maritime and military communications, and emergency services. Equipment typically comprises a transceiver, an antenna (long-wire, dipole, or vertical), a tuner, and sometimes an amplifier. Antenna design and tuning are crucial for efficient radiation at HF wavelengths, which are long relative to many other bands.

In finance, high-frequency trading (HFT) encompasses algorithmic strategies that execute large numbers of orders in fractions of a second. HFT relies on low-latency data feeds, co-location with exchanges, specialized hardware, and optimized software. While it can improve market liquidity, it has attracted concerns about fairness and stability, prompting regulatory reviews in many jurisdictions.