Understanding Sporadic E

00:07:36
https://www.youtube.com/watch?v=glsVmRY9eGk

Résumé

TLDRDen här presentationen handlar om sporadic e, en ovanlig typ av jonosfärisk fortplantning som påverkar signaler vid VHF-frekvenser. Sporadic e inträffar när speciella omständigheter leder till ökad jonisering i E-lagret av jonosfären, vilket kan bryta signaler vid lägre VHF-frekvenser över längre avstånd (ca 700-2500 kilometer). Fenomenet benämns som 'sporadic' eftersom det är svårt att förutsäga och uppträder plötsligt. Orsakerna till sporadic e är ännu inte helt förstådda, även om det finns teorier kopplade till vindskjuvning och ökad metalljonkoncentration. Fenomenet observeras oftast på frekvenser från 50 till 150 MHz. Jämfört med F-lager fortplantning är sporadic e mer lokalt och regionalt, och det är viktigt att skilja det från troposfärisk kanalisering som även kan transportera VHF-signaler över längre avstånd.

A retenir

  • 🌌 Sporadic e påverkar VHF-signaler.
  • 🔭 Svår att förutsäga, inträffar plötsligt.
  • 📡 Normalt mellan 50-150 MHz.
  • ✈️ Möjliggör längre kommunikationsavstånd.
  • 🌀 Förknippas med höga metalljonkoncentrationer.
  • 🗺️ Kartlägger moln genom signalmottagning.
  • 📅 Toppaktivitet mellan maj och augusti.
  • 🌍 Lokalt och regionalt fenomen.
  • 🔁 Skiljer sig från troposfärisk kanalisering.
  • 🤔 Orsakerna fortfarande oklara.

Chronologie

  • 00:00:00 - 00:07:36

    Presentationen handlar om den sällsynta 'sporadiska E'-förökningen i jonosfären, som påverkar VHF-signaler. Till skillnad från F-skiktet, som böjer HF-signaler tillbaka mot jorden, är E-skiktet vanligtvis inte kapabelt till detta. Men under särskilda förhållanden kan områden med ökad jonisering i E-skiktet leda till begränsad skywavespridning av VHF-signaler. Fenomenet, känt som 'sporadisk E', kan orsaka mycket starka signaler och möjliggöra förökning över avstånd mellan 700 och 2500 kilometer.

Carte mentale

Mind Map

Questions fréquemment posées

  • Vad är sporadic e?

    Sporadic e, även kallad e-skip, är en jonosfärisk fortplantning genom högt joniserade områden i E-lagret av jonosfären, som kan bryta VHF-signaler över längre avstånd.

  • Hur påverkar sporadic e VHF-signaler?

    Sporadic e möjliggör kortvarig himmelvågsfortplantning av VHF-signaler över längre avstånd, vanligtvis mellan 700 och 2500 kilometer.

  • Vilka frekvenser påverkas av sporadic e?

    Sporadic e påverkar vanligtvis frekvenser mellan 50 och 150 megahertz.

  • Är sporadic e förutsägbar?

    Nej, sporadic e är svår att förutsäga på grund av att orsakerna till fenomenet ännu inte är helt förstådda.

  • Hur kan man skilja sporadic e från troposfärisk kanalisering?

    Sporadic e dyker upp och försvinner plötsligt medan troposfärisk kanalisering byggs upp och avtar långsammare. Sporadic e förbinder ofta många olika platser, till skillnad från signaler genom kanalisering.

  • När är sporadic e-aktivitet vanligast?

    Aktivitetstoppar för sporadic e inträffar mellan maj och augusti i norra halvklotet, med mindre toppar i december och januari.

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Défilement automatique:
  • 00:00:00
    hello and welcome to this presentation
  • 00:00:02
    understanding sporadic e in this short
  • 00:00:05
    presentation we'll provide an overview
  • 00:00:07
    of sporadic e and The Uncommon type of
  • 00:00:09
    ionospheric propagation that primarily
  • 00:00:12
    affects signals at VHF frequencies
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    as you may already know the ionosphere a
  • 00:00:18
    layer of charged particles surrounding
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    the Earth consists of several layers
  • 00:00:23
    one of these layers the F layer can
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    refract or bend signals at HF
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    frequencies back towards the Earth
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    enabling very long distance
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    Communications under the proper
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    conditions
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    this is often called skywave propagation
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    however at VHF and higher frequencies
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    signals reaching the ionosphere are
  • 00:00:43
    generally not refracted back to Earth
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    and simply pass through the ionosphere
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    and into space
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    below the F layer there's another layer
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    of the ionosphere called the e-layer but
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    under normal circumstances the e-layer
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    is not capable of refracting either HF
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    or VHF signals back towards the Earth
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    however under special circumstances
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    patches or regions of increased
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    ionization in the e-layer can refract
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    signals at lower VHF frequencies thus
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    enabling limited skywave propagation
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    over longer distances
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    sporadic e sometimes also called e skip
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    or ES refers to propagation by means of
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    these highly ionized regions or clouds
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    in the e-layer of the ionosphere
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    this phenomenon takes place at altitudes
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    of about 100 kilometers above the
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    Earth's surface and can last for minutes
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    or even up to an hour or more
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    the signals propagated by sporadic e
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    often have very low path loss and
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    therefore lead to high received signal
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    strengths at the receiver
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    sporadic e can also propagate signals
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    for long distances typically in the
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    range of 700 to 2500 kilometers
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    because of the lower altitude of the
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    e-layer these distances are somewhat
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    lower than the distances achievable with
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    f layer propagation of HF signals
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    this mode of propagation is called
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    sporadic because it's difficult to
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    predict but it's still common enough to
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    cause problems
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    for example European TV broadcasters and
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    American FM radio broadcasters moved up
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    from their original lower frequencies in
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    part to avoid issues caused by sporadic
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    e
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    unlike F layer propagation which is
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    usable across most of HF at different
  • 00:02:36
    times of the day or different days of
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    the year sporadic is only usable at
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    higher HF frequencies and lower VHF
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    frequencies
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    it's most commonly seen around 50
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    megahertz and on rare occasions it may
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    extend above 150 megahertz
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    another way of thinking about sporadic e
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    is that it increases the maximum usable
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    frequency or muff
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    this is the highest frequency that can
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    be used for Sky wave propagation and is
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    usually no higher than 30 megahertz
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    the dimensions of these clouds have
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    increased e-layer ionization are
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    difficult to measure they usually are
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    tens of meters to a few hundred meters
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    thick and from several hundred meters up
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    to two kilometers wide
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    it's important to remember that
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    sporadici is a local or Regional
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    phenomenon that is it only affects
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    propagation over certain geographical
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    regions we'll talk more about this on
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    the next slide
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    this is different from standard F layer
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    propagation at HF frequencies which
  • 00:03:37
    tends to be more uniform over
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    hemisphere-sized regions
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    we can map the location and dimensions
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    of sporadic e clouds by looking at
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    reception reports between Pairs of
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    stations
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    if we draw lines between transmitters
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    and receivers the intersection of these
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    reports will often show the rough size
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    and Center position of the cloud
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    sporadic e clouds are however not
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    stationary and tend to move slowly over
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    the course of their appearance
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    in the northern hemisphere this motion
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    is generally North to Northwest and is
  • 00:04:11
    caused by both winds in the upper
  • 00:04:12
    atmosphere as well as the Earth's
  • 00:04:14
    rotation
  • 00:04:17
    we've discussed barenaki in some detail
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    but have yet to talk about what causes
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    sporadic e
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    there are in fact many different
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    theories about the origins of sporadic e
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    and as yet there is still no definitive
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    universally accepted cause
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    one of the more popular theories is that
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    wind shear or other types of violent
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    weather create thin layers of e-layer
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    ionization
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    experiments have shown that sporadic
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    e-clouds contain high concentrations of
  • 00:04:44
    metallic ions
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    however the lack of a clear measurable
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    cause makes sporadic e difficult to
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    predict
  • 00:04:52
    it's known that Peaks and sporadic
  • 00:04:54
    activity occur between May and August
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    and the Northern Hemisphere with some
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    smaller peaks in December and January
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    and while there are studies that suggest
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    that spradiki may somehow be linked to
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    meteor activity or solar activity there
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    is still no conclusive correlation
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    between these and the appearance of
  • 00:05:14
    sporadic e
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    before we end this presentation we need
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    to briefly mention another way that VHF
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    signals may be propagated over long
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    distances
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    sharp changes in the troposphere's
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    refractive index can cause ducts that
  • 00:05:29
    propagate VHF signals and this is
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    therefore referred to as tropospheric
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    ducting
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    although they work in different ways
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    both tropospheric ducting and sporadic e
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    can produce strong signals over large
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    Geographic areas so it's helpful to
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    understand how to differentiate between
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    them
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    as we saw earlier sporadic e-clouds can
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    connect many different locations whereas
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    inducting signals usually only propagate
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    between endpoints or sometimes along the
  • 00:05:58
    path between them
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    sporadic e tends to appear and disappear
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    rather suddenly but tropospheric ducting
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    normally builds up and Fades out more
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    slowly and thus also tends to last
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    longer than sporadic e-clouds
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    let's end with a brief summary the
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    ionosphere does not normally support
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    skywave propagation at VHF frequencies
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    in the same way that is commonly seen
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    with lower frequency HF signals
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    sporadic e refers to VHF Skyway
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    propagation that's enabled by clouds of
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    Highly ionized particles in the e-layer
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    of the ionosphere
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    generally speaking sporadic e is only
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    seen at frequencies from about 50 to 150
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    megahertz
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    and achievable distances using sporadic
  • 00:06:44
    e are on the order of 700 to 2500
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    kilometers
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    the size and location of sporadic e
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    clouds can be approximately mapped by
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    plotting lines connecting transmitters
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    and receivers and then looking at their
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    intersection
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    the cause or causes of strategy are
  • 00:07:03
    still not completely understood making
  • 00:07:05
    sporadic e difficult to predict
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    and finally both sporadic e and
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    tropospheric ducting can propagate VHF
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    signals over longer distances but these
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    phenomena can be differentiated in a
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    number of different ways
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    this concludes our presentation
  • 00:07:21
    understanding sporadic e
  • 00:07:23
    if you'd like to learn more about other
  • 00:07:25
    propagation modes or about rhodium short
  • 00:07:28
    solutions for radio communications
  • 00:07:29
    please see the links in the video
  • 00:07:31
    description
  • 00:07:33
    thanks for watching
Tags
  • sporadic e
  • jonosfär
  • VHF
  • sändning
  • troposfärisk kanalisering
  • HF-signaler
  • himlevåg
  • kommunikation