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Private Line covers what has occurred, is occurring, and will ocurr in telecommunications. Since communication technology constantly changes, you can expect new content posted regularly.

Consider this site an authoritative resource. Its moderators have successful careers in the telecommunications industry. Utilize the content and send comments. As a site about communicating, conversation is encouraged.

Writers

Thomas Farely

Tom has produced privateline.com since 1995. He is now a freelance technology writer who contributes regularly to the site.

His knowledge of telecommunications has served, most notably, the American Heritage Invention and Technology Magazine and The History Channel.
His interview on Alexander Graham Bell will air on the History Channel the end of 2006.

Ken Schmidt

Ken is a licensed attorney who has worked in the tower industry for seven years. He has managed the development of broadcast towers nationwide and developed and built cell towers.

He has been quoted in newspapers and magazines on issues regarding cell towers and has spoke at industry and non-industry conferences on cell tower related issues.

He is recognized as an expert on cell tower leases and due diligence processes for tower acquisitions.

« You might as well be on Mars | | Consumer Reports Annual Cell Phone Plan Report »

January 06, 2004

Posted by Tom Farley & Mark van der Hoek at 02:16 AM

How long does it take for a radio signal to go from Earth to Mars?

The line art below is from a 1960's Bell System ad detailing their efforts with communication satellites. The ad shows an early computer simulation, possibly drawn on a plotter, quite a contrast from today's marvelous, animated, full color renderings. Click here to view the entire ad in much finer detail. Warning: it's quite a large file.

I've had difficulty finding out exactly how long it takes for a radio signal to go from Earth to Mars. Turns out that many answers can be correct since the distance from our planet to Mars varies so greatly. Here's the problem well explained:

Question

How long does it take for a radio signal to go from Earth to Mars?

Asked by: Richard Boulais

Answer

Radio signals are electromagnetic waves, such as light or X-ray. The speed of electromagnetic waves in vacuum, is 300000km/sec (approximately).

In order to calculate the time of travel with this speed from Earth to Mars, we need to know the distance.

When the Mars and the Earth are at the opposite sides of the Sun, the distance is the largest: approximately: 378 million km. The time needed for an electromagnetic wave to cover this distance is approximately: 21 minute.

The closest distance between Mars and Earth is 78 million km, the time in this case is: 4.3 min.

So the time of travel between Earth and Mars is between 4.3 minutes and 21 minutes, depending on the actual distance between the two planets.

Answered by: Ferenc Szekely, Ph.D., Physicist, ELTE, Budapest, Hungary

Source: http://www.physlink.com/Education/AskExperts/ae381.cfm

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