Saturday, January 29, 2011

Radio Is All Sound. So Radio Waves Travel At The Speed Of Sound

The thing that passes as "news" nowadays.....

So I mentioned a week ago about the Bears-Packers game that had some historical context way back when they last met in the playoffs in 1941. The Packers won the game last week and will meet the Pittsburgh Steelers in the Superbowl.

So of course, there's plenty of news hype leading up to the game. This news article examines some die-hard Packers fans (is there any other type?) who watch the game on TV, but listen to the audio from the radio broadcast.

Many fans like to turn down the sound on the TV set and listen to announcers Wayne Larrivee and Larry McCarren of the Packers Radio Network.

But then there's a problem.

"I can't watch with no sound because of the three-second delay on Fox-ATT-Uverse coverage," said Bruce West of Green Bay. "The radio coverage is way ahead of TV."

Some people get frustrated when they hear the outcome of a play and then see it unfold on the screen.

OK, so that could be a minor problem. But so far, there's no physics involved here, until the writer tries to explain why there is this problem.

It's physics: Radio signals traveling at the speed of sound arrive first because the tower is relatively close by and the TV signal traveling at the speed of light must go 23,000 miles up and 23,000 miles back to Earth.


Radio signal, as any physics student in high school can tell you, is also an electromagnetic wave. It just happens to have a longer wavelength than, say, visible light, but it is still an electromagnetic wave, and thus, still travel at the speed of light, NOT at the speed of sound. Now notice that this can't be a typo. The writer did differentiate the radio signal from the TV signal which is "... traveling at the speed of light...". We all make typos. *I* make tons of typos. So I did consider that maybe the writer meant to type "speed of light" instead of "speed of sound". But from this paragraph, naaah! I don't think this is a typo. It is just bad understanding of basic physics.

So here, the delay isn't caused by the signal having different speeds, but rather how they are transmitted. If one listens to satellite radio, for example, such signal will still have to go through that long path to a satellite before being transmitted back down. Has nothing to do with "speed of sound".

Both writer and editor need to go back and take high school physics.


1 comment:

laser_jock said...

at 186,000 mps, a roundtrip to a GEO satellite is about 1/4 seconds. The 3 second delay that people are hearing is likely due to the tape delay system that live broadcasters must use in order to capture and block profanity and various wardrobe malfuntions.