Blinded by the Sun

sun

Maybe you’ve experienced the following when you’re driving either to or from work: you’re heading up a street that basically runs East-West, approaching a stoplight that usually makes the chaos of traffic conform to its binary demands.You’re either somewhat early coming into the office – or late departing – so the Sun has either just come up over the horizon – or is just about to set. As you approach the stoplight, mirabile dictu (or expletive – if you are a profane soul like me), all the angles are lining up such that the Sun appears to be moving directly behind the stoplight.Sure enough – when you finally come to a stop in the queue of cars – the Sun is now directly behind the stoplight.Despite your $200 pair of polarized, ultraviolet blocking, Bono-approved sunglasses – you cannot even begin to see the condition of the stoplight. Is it RED – is it GREEN – is it even THERE? Thankfully you are not first in line and like Falstaff can take the solace of a soldier in the hind ranks that you will very likely survive – this time by observing the car in front of you and moving forward when it does.

What has just happened to you is essentially what happens to every satellite dish during an approximately weeklong period twice a year, once a day, during the weeks around the Spring and Fall Equinoxes.Like you, the stoplight, and the Sun – the parabolic dish that gathers the RF signal from the satellite at which it is aimed is ‘blinded’ when the Sun moves directly behind the satellite from the POV of the dish.The signal normally hitting the dish after its 22,300 mile journey from the geostationary satellite is comparable in strength to the light from – oh say – a match.And a match is (WARNING – Pathetic Pun Alert!) clearly no match for the light of the Sun (boo!…hiss!).So – when satellite dish, satellite, and Sun come perfectly in line, the incoming, rather feeble satellite signal is overwhelmed and washed out by the vast amount of radiation – RF noise basically – that is consistently generated by the Sun.As the undiscriminating satellite dish still feeds this very powerful, nothing-but-noise signal to the now baffled satellite receiver, it in turn loses its lock on the satellite signal.This can last as long as 10 minutes until the Sun has moved on to the West to play the same trick on satellite dishes further East – and the satellite receiver can again discriminate and recover its normal signal.

Basically – there is little to be done to prevent or ameliorate this (short of expending extravagant sums of money for capacity on differing satellites as well as on redundant equipment).Outage times can be decreased by employing a larger diameter and hence narrower focused dish.But even the largest dishes are unable to avoid at least a moment or two of downtime during the peak sun outage periods.

The physics and spherical trigonometric details behind Sun outages are complex – and beyond the scope and intent of this post (not to mention my declining intellect).If you’d like to learn more about these complexities, Intelsat has a pretty good article about it. As does geo-orbit.org. Both do a pretty good job of describing the mechanics behind sun outages.

And – if you’d like to figure out the Sun outage date/times and durations for your site – here is another good link for that:

http://www.satellite-calculations.com/SUNcalc/SUNcalc.htm

On that site, assuming you are a Mainstream VSAT customer – you’ll want to choose AMC-15 (105.05 W AMC-15) as the satellite.Knowing your latitude and longitude is best – but you may also choose the largest city close to your location to come up with date/times & durations that will still be very close to those at your exact location.For Band – choose KU – and for Antenna size choose 1.0 or 1.2 Meter (no need to worry about the Antenna Pointing fields).Finally – choose your Time-Zone – and hit “Calculate”.

Beyond the bi-annual extraterrestrial meddling, Mainstream Data has a very robust satellite system with one-way and two-way VSAT options. Please visit our satellite information page to learn more, or contact us with any questions about your satellite needs.David Frymire
Mainstream Data Satellite Operations