What is HF Propagation?
Without propagation, all radio communication would be limited to line-of-sight. Unlike VHF and UHF, HF (10M-160M) interacts with the atmosphere, enabling long-distance communication.
Why is HF Different?
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Lower frequencies mean longer wavelengths, which interact with the ionosphere differently.
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HF propagation depends on many various factors, including frequency, solar activity, and time of day.
Key Factors Affecting Propagation
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Frequency: Determines range and time-of-day effectiveness.
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Grey Line: The transition between night and day enhances propagation.
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Ionosphere: The upper part of Earth’s atmosphere which refracts and reflects HF radio waves back to earth. It is Influenced by sunspots, K-index, solar storms, and CMEs.
Useful Resources
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Websites: hamqsl.com, prop.kc2g.com for real-time solar data.
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Software: VOAProp (signal strength maps), HamClock (Linux & Rasp. Pi App).
Choosing a Frequency
The best frequency to use depends on location, time, and solar conditions. General trends:
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Below 10 MHz (“Vampire Bands”) – Best at night.
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Above 10 MHz (“Farmer Bands”) – Favor daylight, dependent on sunspots.
Band Overview
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160M (1.8-2.0 MHz): Short-range by day, long-range at night, noisy in summer.
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75-80M (3.5-4.0 MHz): Local during the day, long-range at night, great for NVIS.
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60M (5 MHz): Medium-range by day, long-range at night, shared with government/military.
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40M (7.0-7.3 MHz): Local/regional by day, excellent DX at night.
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30M (10.1-10.15 MHz): Digital/CW only, consistent propagation.
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20M (14.0-14.35 MHz) & Above: Primarily daytime bands, dependent on MUF and solar cycle.
Summary
By understanding propagation trends and solar conditions, you can always find an open band. Experience makes prediction easier—so get on the air!
More Resources
Here’s a link to the easy-to-read Solar Conditions & Ham Radio Propagation, Courtesy of W5MMW