Search results

The NOAA/GML Solar Calculator provides critical data for **solar position** and timing, including sunrise, sunset, and solar noon, for any geographic location on Earth. Users can input specific dates and times, or select from predefined locations such as World Cities, U.S. Cities, GML Observatories, and GML Data Sites. The interface allows for precise geographical input by dragging a red pin on an interactive map, complemented by extensive time zone selections and UTC offset adjustments. Key outputs include the Equation of Time, Solar Declination, and the sun's azimuth in degrees at local time. The tool also generates comprehensive sunrise/sunset tables for an entire year, opening these data sets in a new browser tab for easy access and analysis. While the calculator remains operational, NOAA explicitly states it is no longer actively supported or maintained, advising users that accuracy and functionality cannot be guaranteed, and no further updates or technical support will be provided. Despite the lack of ongoing support, the resource details the underlying calculations and offers spreadsheets for users interested in performing their own solar data computations. It also includes links to older versions of the solar calculator and a glossary of relevant terms, serving as a reference for understanding solar mechanics and their impact on radio propagation.

Understanding radio wave propagation is fundamental for effective HF communication, and this guide from the Galway Radio Club elucidates the principles behind _Near Vertical Incidence Skywave_ (NVIS) operation. It begins by contrasting NVIS with line-of-sight and surface wave propagation, highlighting its utility for reliable regional coverage, particularly in challenging terrains or within the skip zone. The document explains how NVIS leverages high-angle radiation, refracting signals from the ionosphere to return to Earth within a circular region, typically up to **650 km** (400 miles) from the transmitter. The guide delves into critical factors influencing NVIS, such as the _critical frequency_ (Fo) and the Maximum Usable Frequency (MUF), emphasizing their dependence on solar activity, time of day, and season. It provides practical advice on frequency selection, noting that 40 meters is often the highest daytime NVIS band, with 60 meters and 80 meters favored as darkness falls. The author, EI5DD, suggests using an ionogram for real-time propagation data, considering it more reliable than generic ham-clocks. Antenna considerations are also covered, recommending dipoles, inverted vees, or phased dipoles positioned 0.1 to 0.25 wavelengths above ground for optimal high-angle radiation. The document mentions mobile NVIS setups, including military configurations and commercial options like the Barrett Communications roof-rack antenna, which can cost around **£2000.00**. It concludes by reinforcing NVIS as an essential technique for national emergency communications, with 5 MHz (60m) and 80 meters being primary bands for daytime and nighttime operations, respectively.