Simply put, SNG means "Satellite News Gathering,"  or, using satellites to facilitate live television pictures.  

Big deal. I see live field reporters every day on the local news.  How's this different?

First, you have to understand a little about radio waves.  

All radio energy travels in waves, and is measured in Hertz (Hz), meaning cycles per second. This is where radio "wave" comes from.  The chart on the left shows all forms of electromagnetic radiation, of which radio is a part.  Longer waves are on the left, shorter waves on the right.  AM broadcast radio has about 1 million cycles per second.  (1 MHz)  Each cycle is almost 300 meters apart.  FM radio, sitting around 100 MHz, is much shorter, around 3 meters between waves.  Mobile satellite uplinks work at 14,000 MHz, only 2 centimeters between waves!  Radio waves that high in frequency are called microwaves, and  travel in straight lines only.

When you see live shots on the local news, they are using a technology called Terrestrial microwave communication.  The vehicle that does these live shots has a tall mast that extends from the roof, sometimes up to 70 feet high (above left).  On the top of this mast is a parabolic dish antenna (right) that directs microwaves toward a receive site (above right).  These microwaves are around 2 GHz, very close to the microwaves that cook food in a microwave oven.  The receive sites are mounted on the TV station's tower, or other tall locations.  The drawing directly above shows how terrestrial microwave works.  As long as there is a clear "line of sight" between the two antennas, the system will work.  If there is any tall hills or buildings between the antennas, the link will not work.  Even if there is completely clear sight between antennas, the curvature of the earth (below) becomes a limiting factor.  If the antenna is raised higher, it can "see" farther, just like you can see miles away from a mountain top.

So, while this system works great for local communication, it won't do much good in order to communicate over large distances.  As mentioned above, the higher the antennas are, the further the radio horizon is.   By placing a relay station on a mountain top, the range of communications can be extended (below).

By placing a relay station up high on a hill, overall range of the system is extended.  On the right, there is a coverage map of a typical repeater.  Strong signals are close to the X in the center, but terrain between the X and other location can effect signal strength.  That's why a station on a hill 20 miles away will have a better signal than one in a valley 5 miles away.  But... You only can go so high.  This is where satellites come in.

The view from 22,000 miles above the Earth lets the satellite relay see an entire continent.  Unlike the coverage map above for the hilltop repeater which covers Washington DC and its suburbs, the satellite's coverage map includes all the USA, and most of Canada and Mexico.  Special spot beams are directed out towards Hawaii.  Since the angle between transmitter and receiver is much higher in the satellite example, there is much less chance of buildings or hills blocking the signal.

Now I am less confused... I think.  How do you find a tiny satellite 22,000 miles up?

Thankfully, all the communications satellite stay "parked" in the same place in the sky, right above the equator.  This is called a geosynchronous orbit, meaning the satellite moves at the same speed at the Earth's rotation, making it appear in the same place all the time.  Other orbits include asynchronous, which includes low orbit satellites such as the space shuttle.  These orbits are only a few hundred miles up.  Polar orbits stay fixed in space as the Earth rotates below.  The chart on the left shows the North American arc of Ku-band satellites.  Uplink operators know what part of the sky they need to start searching to find a satellite.

Satellites are pushed into orbit via rockets, often launched from areas close to the equator.  The vehicle on the left is a Delta.  Rockets launched from the equator need less fuel to get their payload into geosync orbit.  That orbit is about 88 times higher than the space shuttle typically goes, and it requires a rocket with lots of fuel.  Equatorial launches get a boost from the Earth's rotation.  Since the Earth is moving through space fastest on the equator, the boost effect is greatest there.  Once a satellite is in orbit, it has enough fuel to remain for around 10-12 years.  Later in its life, it can't keep a steady orbit and becomes inclined.  Once they get too sloppy, they can either be deorbited like MIR, or moved to a high "graveyard" orbit, which is more common among the high geosync sats.  Satellites in the arc are spaced 2 degrees apart at their closest.  This means that a dish movement of a few inches can mean having or not having the signal.  Once one satellite is identified, it orients the operator and they can then go easily anywhere else in the arc.  The most stressful part of a SNG operator's day can be quickly "finding a bird" during a breaking news story.  A good operator can find the correct satellite in about 5 minutes.

How do you identify a satellite?

Full 500MHz span view

SBS-6                                    GE-5                                  Telstar-4                             Telstar-6

SBS-6 has a very identifiable pattern, once zoomed in.

What do sat trucks look like? Where do they come from?