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Re: "spontaneous" LEILA activation


Well, let's not be too hard on this radar system.  After all, it was what
probably helped us determine that AO-40 was in one piece after the



on 9/25/01 3:35 PM, Peter Guelzow at peter.guelzow@arcormail.de wrote:

> Rolf Niefind wrote:
>> May be the old french system for radioloacation  " S Y L E D I S " is back ??
> Most likely it is the "Pave Paws" 70cm high power radar which gave
> us a lot of trouble when trying to comand AO-13 via 70cm uplink...
> I remember that the QRM was mostly there when the S/C was visibible
> for US and UK..   It was clean when over asia etc..
> If you put an unmodulated carrier on the transponder,m you can here this
> kind of "clicking" which is probably due to overload of the input agc etc..
> 73s Peter
> The following is from an article written by me in 1993 for the
> AMSAT-DL Journal and translated by Don Moe, DJ0HC/KE6MN).
> What we see on LEILA is probably related to this?
> Since 1987 the US Air Force has been operating
> a total of four so-called "PAVE PAWS" radar
> systems located in the states of Texas, Georgia,
> California and Massachusetts. The first such in-
> stallation went into operation in 1979.
> The radar system serves primarily to recognize
> launches of ship-based and intercontinental bal-
> listic missiles (ICBMs) and to track their trajec-
> tories. Additionally it also simultaneously ob-
> serves and tracks more than 6000 satellites and
> other objects in Earth orbit. The data are sent to
> NORAD in Colorado for analysis. Orbital param-
> eters and Kepler elements for nearly all satellites
> are administered and published there, including
> among others weather and naturally amateur
> radio satellites. This data is available at no charge
> over a variety of computer networks.
> Each of these gigantic "PAVE PAWS" radar an-
> tennas consists of so-called phased arrays [1].
> These phased arrays are built around thousands
> of separate antennas in order to generate a direc-
> tional radar beam to scan the skies. In contrast to
> customary radar installations in which a parabolic
> dish is mechanically turned and aimed, the direc-
> tional control is determined by changing the
> phase angle between the individual dipole ele-
> ments. Rather than taking minutes, a computer
> can electronically aim at any desired point in the
> sky within a few milliseconds!
> A "PAVE PAWS" radar is built around a three-
> sided, 32 meter high building and can cover an
> arc of 240 degrees. Phased array antennas with a
> diameter of 31 meters are mounted on two sides
> of the building. Each side can hence scan 120 de-
> grees of azimuth and 80 degrees in elevation.
> The transmitter power is provided by transistor-
> ized amplifier stages consisting of four 100 Watt
> transistors combined in each transmitter module
> to drive a single radiating element. This is re-
> peated for a total of 1792 elements. 1792 times
> 400 Watt requires over 700 Kilowatt of pure
> transmitter power, not considering the enormous
> antenna gain! Objects with a surface area of 10
> m2 can thus be observed at a distance of nearly
> 7000 km!
> Two older early warning systems for ballistic
> missiles (BMEWS) also existed in Thule, Green-
> land and Fylingdale, Yorkshire, England. In the
> meantime both BMEWS systems have been con-
> verted and modernized to PAVE PAWS radar
> installations.
> The PAVE PAWS radar in Thule, Greenland
> went into operation in June, 1987. The English
> system followed a few years later. In contrast to
> the radar in Greenland, the English PAVE PAWS
> radar has even a third antenna array and can thus
> cover an entire 360 degree circle. Each of the
> three antenna surfaces consists of more than 2500
> individual antennas.
> Unfortunately the operating frequencies of PAVE
> PAWS radars lie within the 70cm amateur radio
> band, and in particular between 432 MHz and
> 445 MHz. One of the three broad-band main car-
> riers is almost exactly on 435 MHz and a second
> one is close to 439 MHz. The frequency spectra
> also overlap to some extent. The 435 MHz sat-
> ellite segment is thus particularly affected. Ingen-
> iously the range below 432 MHz is not occupied
> at all. Only around 422 MHz do we find another
> carrier.
> At the enormously high radiated power levels of
> these radar systems, consequences to satellite op-
> eration are unavoidable. After the new PAVE
> PAWS radar installations went into service in
> Greenland and England, our situation became
> correspondingly earnest, particularly over the
> past few years since the launch of AMSAT
> OSCAR-13, but OSCAR-21 with RUDAK-II is
> also seriously affected.
> To support command station operations,
> OSCAR-13 relies upon separate frequencies to
> allow the command stations direct access to the
> onboard computer. Depending on which
> transponder is active, the command station must
> call either the Mode-B command receiver on
> 70cm or the Mode-L command receiver on 23cm.
> Since Mode-B operation predominates, particu-
> larly during emergencies or during the launch
> phase, the 70cm command receiver plays a very
> important roll.
> Shortly after the launch of AMSAT OSCAR-13
> in June, 1988, I discovered, as the primary com-
> mand station in Europe, that during orbits when
> OSCAR-13 covered large portions of the USA
> only very poor command control was possible. In
> contrast, command control on easterly orbits was
> quite reliable even at very low power levels.
> Therefore we were able to accomplish our tasks.
> Initially we did not even consider radar interfer-
> ence, but suspected faults in our own stations.
> Over the course of time, the apogee of OSCAR-
> 13 has continued to drift further north and the
> satellite correspondingly covers more of the
> northern hemisphere for longer periods of time.
> Unfortunately this also includes the radar instal-
> lations in the northern parts of the USA and of
> course the modernized radar sites in Greenland
> and England. There is practically not a single
> orbit where one of these PAVE PAWS systems is
> not in view of OSCAR-13. In the early stages,
> this was not too serious for the reasons just men-
> tioned. Incidentally, in February, 1993 the apogee
> of OSCAR-13 has reached its northern-most ex-
> cursion at 57.6  and is now gradually moving to-
> wards the equator.
> On the analog transponder of Mode-B, the radar
> interference can scarcely be noticed and nobody
> seems bothered by it. However the interference
> means the end of digital communications via
> satellite. 
> [....]
> During the first two years following the launch of
> AO-13, a reload of the software was indeed re-
> quired on two occasions and the last time it took
> nearly 6 hours to reprogram the onboard com-
> puter because of the radar interference. A portion
> of the upload had to be performed by Graham
> Ratcliff, VK5AGR, in Australia. Because Graham
> lives in the southern hemisphere, he does not suf-
> fer from radar interference, but his access periods
> are much more limited than ours are in the north-
> ern hemisphere.
> The problems that we here in Europe have with
> the 70cm command uplink affect not only
> OSCAR-13, but also AO-21 with its RUDAK-II
> experiment, for example. In this case, the digital
> uplink frequencies are in the satellite band just
> above 435 MHz. The downlink is at the upper
> end of the 2m satellite segment. Although AO-21
> is in a significantly lower orbit compared to AO-
> 13, it is not spared by the radar in Fylingdale.
> Again we have noticed that command access is
> extremely poor when the PAVE PAWS radar is
> within view. Inspection of the disrupted uplink
> blocks have shown an agreement with the pattern
> of interference to AO-13. In FM mode, the pulse
> interference can be heard quite well and sounds
> like crackling noises. On AO-13 or AO-10 these
> same irregular pulses can be readily heard on a
> weak CW carrier as interruptions or crackling
> noises.
> [.....]
> OSCAR-21, like AO-13, has a command receiver
> and uplink frequencies in the 70cm band also.
> The situation here is likewise quite difficult. Only
> low passes in the East can be used at all when the
> English radar is below the horizon. The success
> ratio for uploads of long data files is unfortu-
> nately mostly below 30% so that much time is
> lost to numerous repetitions. On March 25 and
> 26 the radar was coincidentally out of service for
> maintenance and the success ratio rose to over
> 98%! Unfortunately this is only seldom the case
> and for obvious reasons at irregular intervals and
> without prior notice.
> [...]
> Literature
> [1] "Phased-Array Radars", Eli Brookner, Scientific American, February 1985.
> [2] "Wind Profilers at 449 MHz", Rick Palm, K1CE, QST, March 1992
> [3] "Wind Profiler Frequencies", Richard Barth, W3HWN, QST, April 1992
> ----
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Jon Ogden
NA9D (ex: KE9NA)



"A life lived in fear is a life half lived."

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