Mar 07 2010

The Sun Gets in the Way

Published by at 7:18 am under Weather & Sky

Artist's rendition of AMC-21 satellite (from Orbital Sciences Corporation news room)I find out the coolest things by working in television.  Here’s one about a “bird” I don’t normally discuss.

Last week I received an email from PBS Engineering with a list of dates and times when PBS stations will experience satellite interference from the Sun on the AMC-21 satellite. 

Why?

PBS uses AMC-21 to send programming to the stations.  PBS beams it up and each station has a dish to pull it down for pre-recording or broadcast. 

AMC-21 is a geosynchronous satellite so it orbits the earth at the same speed the ground is moving.  From our perspective on earth, the satellite never appears to move so we can point our dishes to just one place and never have to adjust them.  Unfortunately the sun reaches that same sweet spot twice a year.

In the weeks near the equinox the sun gets in the way.  For about 15 minutes per day the sun’s path is directly behind (in line with) the satellite.  The sun emits a lot of radio waves and in this position it confuses our dish receivers.  The dates and times of the interference depend on your location on earth.  It’s worse in heavy sun spot years.  This year “there should be minimal Ku-Band sun outage disruptions due to the low level of solar activity” according to PBS. 

For WQED most of the interference happened earlier this week.  Our last episode will be today from 3:45pm to 3:59pm but you’ll never notice it on the air.  We correct for it in our engineering department. 

The sun is on the move (actually the earth is traveling around it) so this phenomenon will stop soon.  To read more about it, see this informative article from Australia’s IPS Radio and Space Services.

And yes, some people call satellites “birds.”  It’s confusing!

(artists rendition of the AMC-21 satellite from Orbital Sciences Corporation)

2 responses so far

2 Responses to “The Sun Gets in the Way”

  1. Dallason 07 Mar 2010 at 12:00 pm

    Very interesting! How do they set the speed of the satellites? (Plz pardon me if this is a ‘stupid question.’)

  2. Kate St. Johnon 08 Mar 2010 at 7:17 am

    Dallas, thanks for your question. I didn’t know the answer but just now learned that the speed is determined by its distance from earth. Check out this cool website with the answer! http://www.freemars.org/jeff/speed/index.htm
    The interesting thing is that all the geosynchronous satellites have to be at the same altitude, so it must be pretty crowded up there.

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