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Re: [MSG-1] Eurobird 9A

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  • Alan Sewards
    James, While I see your point, I don t altogether agree. When it comes to TV sats in the Ku band, the equipment is so standardized that nobody should install
    Message 1 of 41 , Mar 1, 2009
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      James,
      While I see your point, I don't altogether agree. When it comes to
      TV sats in the Ku band, the equipment is so standardized that nobody
      should install larger dishes by design - it just would not be
      cost/effective. The link that was originally provided by HB6 was spec'd
      typically for such a satellite link and worked pretty well for everyone,
      allowing for the shape of the footprint. EB9 was a less good fit, but
      was an old satellite pressed into service and I suspect it did not have
      enough power (EIRP) for the job it was required to do - it certainly did
      not replace HB6 adequately. I just don't know what is going on with EB9A
      (ex HB7?), the original footprint was reasonably satisfactory except for
      the fall-off in Scotland, but should have been compensated for by the
      higher EIRP, which now seems to have vanished. The associated
      instability of the signal also raises questions - either the satellite
      is not properly stabilized (which I suspect), or is still being messed
      about with.
      With regards to margins for rain or snow - the basic link budget
      does include a margin for those, but a reasonable one. Very heavy rain,
      occurring perhaps once in 20 years for ten minutes or so, could produce
      attenuations of more than 10 dB and you would not want to install a dish
      10 dB larger in area just to cope with that situation!

      Best regards - Alan

      James Brown wrote:
      >
      > >
      > >................ which begs the question should Eumetsat be paying for a
      > >satellite service that does not properly serve all their customer base.
      > >Eumetsat need to stop pussy footing about with Eutelsat. They are the
      > >paying customer.
      > >
      > >Regards
      > >Douglas.
      >
      > Hi Douglas and all north of the border! I feel your pain - specially as
      > one who had to re-locate the dish and not just swivel it!
      >
      > But I wonder if a fairer way to look at it is to put our reception -
      > even for software developers dare I suggest - into some kind of context.
      >
      > The primary service is surely to commercial and national governments. I
      > am guessing that these have access to larger dishes and would barely
      > notice the dips in power, save the 12 noon issue.
      >
      > In essence are we not the secondary users, albeit there have been
      > indications that our feedback has been hugely beneficial to even primary
      > users? The ongoing service is paid for through our national government
      > rather than being a charge to us.
      >
      > I am guessing that the choice of the new satellite has involved a cost
      > differential favourable to EUMETSAT.
      >
      > I have no idea about the link power budget for the feed we have access
      > to, but it may be possible for EUMETSAT to negotiate a better figure in
      > the light of our feedback, or to get EUTELSAT to establish a more evenly
      > maintained service. So perhaps there may be a glimmer of light.
      >
      > Failing it all, my dad moved from Aberdeen to Wales many years
      > ago.....;-))
      >
      > James
      > --
      > James Brown
      >
      >
    • David J Taylor
      ... It depends what the diurnal effect is caused by, John. If the uplink signal to the satellite isn t consistent, then we will all see the same variation.
      Message 41 of 41 , Mar 11, 2009
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        John Say wrote:
        > David and Alan,
        >
        > The bad weather effect here seems much more than it was (a frequency
        > effect?), even though the values of SNR, Quality and Strength are
        > generally quite a bit higher. I am using the 4.5.0 dirvers. The
        > Strength value used to be around 48 and is now 60+. There is little
        > diurnal effect. I am surprised that, not being all that far south of
        > Edinburgh, there is so much difference. Cheers
        > John

        It depends what the diurnal effect is caused by, John. If the uplink
        signal to the satellite isn't consistent, then we will all see the same
        variation. If the satellite is wobbling slightly, either in orbital
        position or in beam pointing, then the effects will differ across the
        footprint. The position variation seems to be less than 0.1 degrees
        (azimuth and elevation) although slightly more in elevation. However,
        with the size of the dishes we use, that should be insignificant. How
        accurately the satellite is pointed, and whether that might be varying, I
        don't know.

        The figures from my 4.5.0 system are here:
        http://www.satsignal.eu/mrtg/skystar_stamsund_snr.html

        Quality varies very approximately from about 62-66%, and SNR from about 8
        to about 9dB. With the 4.5.0 drivers, the values appear to be more
        quantised than with the earlier drivers....

        Cheers,
        David
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