F2 propagation
Rare VHF skywave reflection off the F2 ionospheric layer.
F2 propagation, also known as F2-skip, occurs when VHF signals bounce off the F2 layer of the ionosphere. This type of propagation is less common than others, such as sporadic E propagation, but it can carry signals thousands of miles beyond their intended coverage area—much farther than E-skip. F2-skip influences the upper portion of the high frequency (HF) spectrum and the lower part of the very high frequency (VHF) spectrum. Only a narrow slice of F2’s effective range overlaps with the frequencies used by consumer broadcast reception, which is another reason the phenomenon is seldom noticed.
The sun follows an approximately 11-year cycle of activity, marked by rising and falling sunspot numbers. When sunspot activity increases, the F1 layer’s ability to reflect signals improves, aiding high-frequency short-wave communications. The highest reflecting layer, F2, sits about 200 miles above Earth. Ultraviolet radiation from the sun ionizes the gases in this layer. During daytime, especially at the peak of the sunspot cycle, the F2 layer can become heavily ionized. If solar activity is strong enough, the maximum usable frequency (MUF) rises, and the ionization density becomes sufficient to reflect signals well into the 30–60 MHz VHF range. As the MUF climbs, lower frequencies are affected first: the 27 MHz CB band and the amateur 28 MHz 10-meter band, followed by 45–55 MHz TV and the 6-meter amateur band. The F2 MUF generally increases more slowly than the sporadic E MUF.
Because the F2 layer is roughly 200 miles high, a single-hop F2 signal typically travels at least 2,000 miles, with a maximum single-hop distance of about 3,000 miles. Multi-hop F2 propagation has allowed Band 1 VHF reception over distances exceeding 11,000 miles.
F2 reception is directly tied to solar radiation, both daily and over the sunspot cycle. For the best reception, the center of the signal path should be near midday. Outside of a solar maximum, F2 propagation can still occur fairly regularly within about 15 to 20 degrees of the geomagnetic equator, with a peak in spring. This type is usually called trans-equatorial propagation (TEP) to distinguish it from the rarer mid-latitude F2 propagation.
During a solar minimum, the F2 layer mainly propagates signals below 30 MHz (HF), including the 27 MHz CB band and the 28 MHz 10-meter amateur band.
- F2 layer height
- approximately 200 mi above earth
- Single-hop minimum distance
- around 2,000 mi
- Single-hop maximum distance
- up to approximately 3,000 mi
- Multi-hop maximum distance
- over 11,000 mi
- Solar cycle length
- approximately 11 years
- Frequency range affected
- 30-60 MHz VHF spectrum during solar maximum
- Notable reception distance record
- 13,750 km (ARD E2 video from Grünten received in Perth, West Australia, February 8, 1992)
Lore & Background
The F2 layer, the highest-reflecting layer of the ionosphere, receives ultraviolet radiation from the sun, causing ionization of the gases within it. During the daytime when sunspot activity is at a maximum, the F2 layer can become intensely ionized, raising the maximum usable frequency (MUF) into the 30-60 MHz VHF spectrum. The MUF generally increases at a slower rate compared to the Es MUF. A rising MUF initially affects the 27 MHz CB band and the amateur 28 MHz 10-meter band before reaching 45-55 MHz TV and the 6-meter amateur band.
Since the height of the F2 layer is some 200 miles, single-hop F2 signals are received at thousands rather than hundreds of miles, with a minimum of around 2,000 miles and a maximum of up to approximately 3,000 miles. Multi-hop F2 propagation has enabled Band 1 VHF reception to over 11,000 miles. For optimum reception the center of the signal path is roughly at midday. Outside a solar maximum, F2 propagation can still occur somewhat regularly within about 15 to 20 degrees from the geomagnetic equator, with the peak generally in spring; this type is specifically referred to as Trans Equatorial Propagation (TEP) to differentiate it from the less common mid-latitude F2 propagation.
Television pictures propagated via F2 tend to suffer from characteristic ghosting and smearing, although they are mostly stronger and more stable than double-hop sporadic E signals. Picture degradation and signal strength attenuation increase with each subsequent F2 hop.
Reader's Guide
F2 propagation is significant because it enables VHF signals to travel distances far beyond normal line-of-sight or even sporadic E propagation, with single hops reaching thousands of miles and multi-hop paths exceeding 11,000 miles. Its legacy is documented through notable DX receptions spanning decades and continents. In November 1938, 405-line video from the BBC Alexandra Palace television station in London on channel B1 (45.0 MHz) was received in New York. In 1958, a DXer in southern California logged a 45 MHz commercial FM station from Korea via trans-Pacific F2 propagation at 5,000 miles. During October to December 1979, United Kingdom DXers received viewable television pictures from Australian channel TVQ 0 Brisbane via multi-hop F2 propagation. On January 31, 1981, a DXer in Sydney, Australia, received 41.5 MHz channel B1 television audio from the BBC's Crystal Palace transmitter, 10,560 miles away. In 2014, a DXer in southern Portugal received Canal 2 Posada from Argentina (55.251 MHz video) about 8,700 km away. From late March until mid April 2023, a DXer in Kyoto, Japan received various TV signals from the Philippines at 3,200 km. These receptions demonstrate the extraordinary reach of F2 propagation during solar maxima and its value to DX enthusiasts.
Did You Know?
- F2 propagation can reflect signals thousands of miles beyond their intended broadcast area, substantially farther than E-skip.
- A single-hop F2 signal will usually be around 2,000 miles minimum and can reach up to approximately 3,000 miles.
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