TheEC: Not All Snow is the Same in the Satdish

Jan 7, 2017

Your intrepid engineer hard at work. This cocoa ain't gonna drink itself! :)
Credit Lisa Read / RIPR

With the forecast being for 10 to 15 inches of snow (!!!) across the Providence region today, why is your Intrepid Engineer smugly sipping hot cocoa in his kitchen, instead of frantically sweeping mounds of snow from the satellite dish?

After all, longtime EC readers know that snow is, well, sort of the bane of my existence when it comes to the satellite dish.  Normally it takes very, very little...just half an inch...to really nuke our signal levels, and wreak havoc with trying to get NPR, BBC and other national programming from the Public Radio Satellite Service.

So if it only takes half an inch, why is a foot no big deal?  Because it's all about the actual liquid content of the snow.  When it snows and it's this cold out (currently 20F at writing) the snow tends to have very little liquid...it's all big, light, fluffy flakes.  These big flakes add up fast and lead to big snowfall totals, but it's the liquid equivalent that matters.  Air does not affect satellite signals, but water does.  

This is why in my four years of managing WEOS up in "lake effect" country (the Finger Lakes of NY) I can count on one hand the number of times we lost satellite signal because of snowfall.  Despite every winter routinely having a dozen storms that dropped snowfall totals measured in feet.   It was always very cold snow, and thus light and fluffy snow.

Normally here in Providence, we don't get that.  We're just warm enough that when it does snow, it's high-liquid-content snow.  That wet, heavy, obnoxious-to-shovel stuff that often takes down power lines and everyone hates.  Especially our satellite dish!  Doesn't take much liquid to screw up the focal point of a 13ft diameter dish when the signal's coming from a satellite approximately 22,000 miles away (for reference, that's roughly like driving from Providence to Los Angeles, and back, three times.  And then driving to Kansas.)

But today's "hefty" snowstorm is so dry that the satellite dish barely even notices it.  As of 3pm (about 4 hours into the storm) our Eb/N0 reading (a ratio of signal to noise, and a good judge of whether or not snowfall is causing problems) is hovering around 10.5 to 11dB.  Normal is 11-12dB, and we don't lose signal until 3.5dB.  So that's a huuuge safety margin.  The dish heater hasn't fired up once yet!

The circled Eb/N0 level is the key. It's only 1dB below normal. We don't usually lose signal lock until it drops to 3.5dB or so.
Credit Aaron Read

So join our Intrepid Engineer and raise a mug of your preferred beverage for it being just cold enough to keep the snow light and fluffy today!   And fear not, by Tuesday it's supposed to rain and be in the 40's, so bye-bye snow!  :)