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William Hepburn's Daily Tropospheric Ducting Forecast.

Navtex Maritime Safety Information Broadcast Channels

VLF Time Signal Stations, Station List Compiled by William Hepburn, LWCA

The areas noted in the forecast have the necessary atmospheric conditions to produce tropospheric bending of VHF, UHF and/or microwave radio waves. Tropospheric bending extends the range of radio & TV stations well beyond their normal limit and thus increases interference amongst stations as well.

The resource details HF time broadcast stations, categorizing them into "Standard Frequency & Time Signal Broadcast" and "Time Signal Broadcast" types. Standard Frequency & Time Signal Broadcasts, like those on **2.5 MHz** and **5 MHz**, originate from official time observatories and offer continuous standard frequencies, time signals, and often voice announcements, potentially including meteorological data. These stations operate in the SW band. Time Signal Broadcasts also provide continuous time signals, typically with voice announcements, but without the strict observatory origin requirement. The list includes specific frequencies such as 3.33 MHz, 4.996 MHz, 7.85 MHz, 9.996 MHz, 14.67 MHz, 14.996 MHz, 15.006 MHz, and 20 MHz, alongside the primary standard frequencies. Each entry specifies the station's ID time, call sign, geographic coordinates, and operational notes, including languages like _English_, Chinese, Portuguese, Korean, and Spanish. Some entries also indicate decommissioning dates, such as the station on 3.33 MHz scheduled for 2026-06-22.