F2 propagation

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F2 propagation (F2-skip) is the reflection of VHF signals off the F2 layer of the ionosphere. The phenomenon is rare compared to other forms of propagation (such as sporadic E propagation, or E-skip) but can reflect signals thousands of miles beyond their intended broadcast area, substantially farther than E-skip. F2-skip affects the upper ends of the high frequency (HF) spectrum and the low ends of the very high frequency (VHF) spectrum; only a small portion of F2's effective range overlaps frequencies used by consumer broadcast reception, also contributing to the phenomenon being rarely encountered.

Contents

Theory

Solar activity has a cycle of approximately 11 years. During this period, sunspot activity rises to a peak and gradually falls again to a low level. When sunspot activity increases, the reflecting capabilities of the F1 layer surrounding earth enable high frequency short-wave communications. The highest-reflecting layer, the F2 layer, which is approximately 200 miles (320 km) above earth, receives ultraviolet radiation from the sun, causing ionisation of the gases within this layer. During the daytime when sunspot activity is at a maximum, the F2 layer can become intensely ionized due to radiation from the sun. When solar activity is sufficiently high, the maximum usable frequency (MUF) increases, hence the ionisation density is sufficient to reflect signals well into the 30-60 MHz VHF spectrum. Since the MUF progressively increases, F2 reception on lower frequencies can indicate potential low band 45-55 MHz VHF TV as well as VHF amateur radio paths. A rising MUF will initially affect the 27 MHz CB band, and the amateur 28 MHz 10 meters band before reaching 45-55 MHz TV and the 6 meters amateur band. The F2 MUF generally increases at a slower rate compared to the Es MUF.

Since the height of the F2 layer is some 200 miles (320 km), it follows that single-hop F2 signals will be received at thousands rather than hundreds of miles. A single-hop F2 signal will usually be around 2,000 miles (3,200 km) minimum. A maximum F2 single-hop can reach up to approximately 3,000 miles (4,800 km). Multi-hop F2 propagation has enabled Band 1 VHF reception to over 11,000 miles (18,000 km).

Since F2 reception is directly related to radiation from the Sun on both a daily basis and in relation to the sunspot cycle, it follows that for optimum reception the centre of the signal path will be roughly at midday. Outside a solar maximum it can still occur somewhat regularly within about 15 to 20 degrees from the geomagnetic equator, with the peak generally being in spring time. However, this type of F2 propagation is mostly specifically referred to as TEP (Trans Equatorial Propagation) to differentiate it from the less common mid latitude F2 propagation.

The F2 layer tends to predominantly propagate signals below 30 MHz (HF) during a solar minimum, which includes the 27 MHz CB radio, and 28 MHz 10-meter amateur radio band. During a solar maximum, television, amateur radio signals, private land mobile, and other services in the 30-60 MHz VHF spectrum are also propagated over considerable distances. In North America, F2 is most likely to only affect VHF TV channel 2, in Europe and middle east channel E2 and E3 (and the now deprecated channel itA) and in eastern Europe channel R1.

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 signal. Picture degradation and signal strength attenuation increases with each subsequent F2 hop.

Notable F2 DX receptions

See also

Related Research Articles

<span class="mw-page-title-main">Ionosphere</span> Ionized part of Earths upper atmosphere

The ionosphere is the ionized part of the upper atmosphere of Earth, from about 48 km (30 mi) to 965 km (600 mi) above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on Earth. It also affects GPS signals that travel through this layer.

The F region of the ionosphere is home to the F layer of ionization, also called the Appleton–Barnett layer, after the English physicist Edward Appleton and New Zealand physicist and meteorologist Miles Barnett. As with other ionospheric sectors, 'layer' implies a concentration of plasma, while 'region' is the volume that contains the said layer. The F region contains ionized gases at a height of around 150–800 km above sea level, placing it in the Earth's thermosphere, a hot region in the upper atmosphere, and also in the heterosphere, where chemical composition varies with height. Generally speaking, the F region has the highest concentration of free electrons and ions anywhere in the atmosphere. It may be thought of as comprising two layers, the F1 and F2 layers.

In radio transmission, maximum usable frequency (MUF) is the highest radio frequency that can be used for transmission between two points on Earth by reflection from the ionosphere at a specified time, independent of transmitter power. This index is especially useful for shortwave transmissions.

<span class="mw-page-title-main">Very high frequency</span> Electromagnetic wave range of 30-300 MHz

Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF are denoted high frequency (HF), and the next higher frequencies are known as ultra high frequency (UHF).

<span class="mw-page-title-main">High frequency</span> The range 3-30 MHz of the electromagnetic spectrum

High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters. Frequencies immediately below HF are denoted medium frequency (MF), while the next band of higher frequencies is known as the very high frequency (VHF) band. The HF band is a major part of the shortwave band of frequencies, so communication at these frequencies is often called shortwave radio. Because radio waves in this band can be reflected back to Earth by the ionosphere layer in the atmosphere – a method known as "skip" or "skywave" propagation – these frequencies are suitable for long-distance communication across intercontinental distances and for mountainous terrains which prevent line-of-sight communications. The band is used by international shortwave broadcasting stations (3.95–25.82 MHz), aviation communication, government time stations, weather stations, amateur radio and citizens band services, among other uses.

<span class="mw-page-title-main">Sporadic E propagation</span> Type of radio propagation

Sporadic E is an unusual form of radio propagation using a low level of the Earth's ionosphere that normally does not refract radio waves.

TV DX and FM DX is the active search for distant radio or television stations received during unusual atmospheric conditions. The term DX is an old telegraphic term meaning "long distance."

Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another in vacuum, or into various parts of the atmosphere. As a form of electromagnetic radiation, like light waves, radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization, and scattering. Understanding the effects of varying conditions on radio propagation has many practical applications, from choosing frequencies for amateur radio communications, international shortwave broadcasters, to designing reliable mobile telephone systems, to radio navigation, to operation of radar systems.

<span class="mw-page-title-main">Skywave</span> Propagation of radio waves beyond the radio horizon.

In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of the Earth, skywave propagation can be used to communicate beyond the horizon, at intercontinental distances. It is mostly used in the shortwave frequency bands.

<span class="mw-page-title-main">Amateur television</span> Transmission of video in amateur radio bands

Amateur television (ATV) is the transmission of broadcast quality video and audio over the wide range of frequencies of radio waves allocated for radio amateur (Ham) use. ATV is used for non-commercial experimentation, pleasure, and public service events. Ham TV stations were on the air in many cities before commercial television stations came on the air. Various transmission standards are used, these include the broadcast transmission standards of NTSC in North America and Japan, and PAL or SECAM elsewhere, utilizing the full refresh rates of those standards. ATV includes the study of building of such transmitters and receivers, and the study of radio propagation of signals travelling between transmitting and receiving stations.

<span class="mw-page-title-main">6-meter band</span>

The 6-meter band is the lowest portion of the very high frequency (VHF) radio spectrum internationally allocated to amateur radio use. The term refers to the average signal wavelength of 6 meters.

DXing, taken from DX, the telegraphic shorthand for "distance" or "distant", is the hobby of receiving and identifying distant radio or television signals, or making two-way radio contact with distant stations in amateur radio, citizens band radio or other two-way radio communications. Many DXers also attempt to obtain written verifications of reception or contact, sometimes referred to as "QSLs" or "veries".

Non-line-of-sight (NLOS) radio propagation occurs outside of the typical line-of-sight (LOS) between the transmitter and receiver, such as in ground reflections. Near-line-of-sight conditions refer to partial obstruction by a physical object present in the innermost Fresnel zone.

The 10-meter band is a portion of the shortwave radio spectrum internationally allocated to amateur radio and amateur satellite use on a primary basis. The band consists of frequencies stretching from 28.000 to 29.700 MHz.

Near vertical incidence skywave, or NVIS, is a skywave radio-wave propagation path that provides usable signals in the medium distances range — usually 0–650 km. It is used for military and paramilitary communications, broadcasting, especially in the tropics, and by radio amateurs for nearby contacts circumventing line-of-sight barriers. The radio waves travel near-vertically upwards into the ionosphere, where they are refracted back down and can be received within a circular region up to 650 km from the transmitter. If the frequency is too high, refraction is insufficient to return the signal to earth and if it is too low, absorption in the ionospheric D layer may reduce the signal strength.

MW DX, short for mediumwave DXing, is the hobby of receiving distant mediumwave radio stations. MW DX is similar to TV and FM DX in that broadcast band (BCB) stations are the reception targets. However, the nature of the lower frequencies used by mediumwave radio stations is very much different from that of the VHF and UHF bands used by FM and TV broadcast stations, and therefore involves different receiving equipment, signal propagation, and reception techniques.

Amateur radio frequency allocation is done by national telecommunication authorities. Globally, the International Telecommunication Union (ITU) oversees how much radio spectrum is set aside for amateur radio transmissions. Individual amateur stations are free to use any frequency within authorized frequency ranges; authorized bands may vary by the class of the station license.

Band I is a range of radio frequencies within the very high frequency (VHF) part of the electromagnetic spectrum. The first time there was defined "for simplicity" in Annex 1 of "Final acts of the European Broadcasting Conference in the VHF and UHF bands - Stockholm, 1961". Band I ranges from 47 to 68 MHz for the European Broadcasting Area, and from 54 to 88 MHz for the Americas and it is primarily used for television broadcasting in compliance with ITU Radio Regulations. With the transition to digital TV, most Band I transmitters have already been switched off.

This is an index to articles about terms used in discussion of radio propagation.

Tropospheric propagation describes electromagnetic propagation in relation to the troposphere. The service area from a VHF or UHF radio transmitter extends to just beyond the optical horizon, at which point signals start to rapidly reduce in strength. Viewers living in such a "deep fringe" reception area will notice that during certain conditions, weak signals normally masked by noise increase in signal strength to allow quality reception. Such conditions are related to the current state of the troposphere.

References

  1. ↑ "You Tube". YouTube . Archived from the original on 2021-12-12. Retrieved May 14, 2018.
  2. ↑ "Unknown title". Radio-electronics. Gernsback Publications. 30: 136. 1959 – via Google Books.
  3. ↑ "Anthony (Tony) Mann's TVDX page". The University of Western Australia School of Physics. Archived from the original on March 7, 2005. Retrieved April 26, 2005.
  4. ↑ Todd Emslie's TV FM DX Site
  5. ↑ Retro TVDX - F2 into Perth, WA on 8 Feb 1992 chE2 Grunten Germany with FuBK test card, and UK/Eu 6m. , retrieved 2023-04-22
  6. ↑ TVDX Ch A2 625 Lines 2000 utc 18 April 2014 , retrieved 2022-02-05
  7. ↑ AMBS ALLTV Ch.2 Sign-off via Spread-F Propagation: 23:30JST March 16, 2023 , retrieved 2023-04-22
  8. ↑ TV5 on Channl 2 (F2 Propagation): 18:41JST～ April 2, 2023 , retrieved 2023-04-22
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