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    F-35 vs Russian Air Defence

    kvs
    kvs

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    Post  kvs on Fri Mar 08, 2019 2:49 am

    LMFS wrote:
    kvs wrote:All of these early warning "radars" look over the horizon by design.  They bounce their signal off the ionosphere and the surface.   This way they outgoing signal
    can follow the curvature of the Earth for thousands of kilometers.   The reflected signal does the same thing, bouncing between the surface and the ionosphere.

    With modern computer resources, it makes sense to design such "radars" with a set of frequency bands and doing "tomography" on the backscatter.  
    In the 1950s and 1960s it was just the analog return signal that they could use.   That is why there was a preference for a few frequencies.  
    I thought this effect required very long wavelengths to operate. But maybe modern processing can take advantage of both high and low band components of the return and get the same effect as an OTH-B?? When you say "tomography", you refer professing all the frequencies received right? Otherwise I cannot make sense of the term.

    The reflection from the ionosphere is due the the presence of ions and is not fundamentally frequency dependent. Some frequencies will scatter
    more efficiently. But that is neither here nor there. Modern high sensitivity amps (GaN) together with computer processing allows real time
    analysis of backscatter from a wide range of frequencies with varying efficiencies of scatter. This is a species of tomography since tomography
    is the reconstruction of some scanned shape from either transmitted or scattered waves. Seismic tomography is an example.


    User "SOC" was arguing in the Voronezh thread some years ago that this radar could not be a OTH-B (backscatter) radar but maybe OTH-SW (surface wave) radar that could be made smaller but had nevertheless the disadvantage of having shadow zones caused by mountains...

    All radars work on backscatter. SOC has to be more specific before being credible. A passive detector requires a strong signal from the target or from a source
    behind the target (e.g. solar occultation). Phased array early warning radars are not passive detectors. They use a more efficient EM wavelengths to
    detect far objects. But that range is not as limited these days as it was back in the 1960s.
    kvs
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    Post  kvs on Fri Mar 08, 2019 2:51 am

    George1 wrote:so Russian radars can detect F-35?

    The key detail is that they can differentiate them from actual ICBM launches. The days of flocks of geese confusing these systems are
    over. And this is not just apocryphal BS, then it was incompetence back the early 1980s that would result in any confusion.

    GarryB
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    Post  GarryB on Fri Mar 08, 2019 4:15 am

    I remember the Americans thought the Soviets were attacking with a massive launch... till they realised it was a problem with a decimal point being in the wrong place... their massive attack turned out to be the moon rising... fortunately their other sensors didn't indicate an attack so they assumed it was a malfunction...
    Hole
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    Post  Hole on Fri Mar 08, 2019 10:30 am

    Ar, this nasty russians again, using the moon for their aggression! angry lol!
    LMFS
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    Post  LMFS on Sat Mar 09, 2019 4:26 pm

    kvs wrote:The reflection from the ionosphere is due the the presence of ions and is not fundamentally frequency dependent.   Some frequencies will scatter
    more efficiently.  But that is neither here nor there.    Modern high sensitivity amps (GaN) together with computer processing allows real time
    analysis of backscatter from a wide range of frequencies with varying efficiencies of scatter.    This is a species of tomography since tomography
    is the reconstruction of some scanned shape from either transmitted or scattered waves.   Seismic tomography is an example.
    Ok thanks kvs. I understand the reflection of electromagnetic waves on conductive layers, just thought the phenomenon was not really effective outside such frequencies. But maybe new technology and specially processing can change such accepted realities. Will keep an eye on the issue.


    User "SOC" was arguing in the Voronezh thread some years ago that this radar could not be a OTH-B (backscatter) radar but maybe OTH-SW (surface wave) radar that could be made smaller but had nevertheless the disadvantage of having shadow zones caused by mountains...

    All radars work on backscatter.   SOC has to be more specific before being credible.   A passive detector requires a strong signal from the target or from a source
    behind the target (e.g. solar occultation).    Phased array early warning radars are not passive detectors.    They use a more efficient EM wavelengths to
    detect far objects.   But that range is not as limited these days as it was back in the 1960s.
    [/quote]
    I need to look deeper this surface-wave type. I thought it was meant to operate only in naval surveillance and not on land...
    kvs
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    Post  kvs on Sat Mar 09, 2019 5:00 pm

    Short wave radio operates over a rather wide range of frequencies and it uses scattering off the ionosphere. But the full potential
    of ion reflection has not been tapped. Ionization is substantial down to 70 km (upper mesosphere) in the high latitudes due to
    auroral belt electron precipitation. And galactic cosmic rays (GCR) ionize a layer at around 13 km spanning from the geomagnetic poles
    to the subtropics (the high latitude confinement is not as severe as for auroral belt electrons since GCR have GeV energies when
    they impact the atmosphere and disintegrate into a cascade of particles as in particle accelerator experiments). Since these
    ionization layers occur at much higher densities than the ionosphere, the efficiency of scatter from smaller wavelengths increases.
    But even wavelengths shorter than the mean distance between ions in the low density ionosphere will still scatter since we are
    dealing with substantial layer thickness and not a single ion.

    High sensitivity phase array "radars" coupled with massive available real time computational resources enable new approaches to scatter
    waves of various frequencies from regions of the atmosphere not previously used for this purpose. Russian upper atmosphere science
    is rather strong especially when dealing with EM aspects and ionization. Various critics with zero education in this area simply have
    no clue what is possible. Their only metric is how much money is spent. But the US itself is an utter failure in this regard since it
    has numerous large scale projects that "ran out of money" (due to corruption) and were never finished.

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