Satellite lag time

I frequently watch the news. The guests are connected thru some kind of satellite link. There is a noticable lag time during the conversation. It can be very annoying. You have to be willing to talk over someone to be able to make your point sometimes.

If the guest were on a confrence call (video stream), would the lag be as noticable? You would think a land link would be better for remote news interviews.

Of course if it were better, they would be doing it. So....???

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It all depends on where the transmission is coming from. IIRC, the time to transmit over a satellite is ~400-600 milliseconds between the Pacific and the Atlantic. Well, the round trip ping time was averaging around 1000ms. The signal has around 45,000 miles to travel.

However, most transmissions are scrambled. So...

Encode ===>scramble ===>transmit ===>receive ===>de-scramble == => view (re-broadcast local) and then reverse the process to send a signal back. If the signal needs to be relayed then more time will be added to the transmit/receive period.

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Off the top of my head, geosynchronous satellites are at an altitude of about 22,000 miles. If you are in contact with someone through such a link it takes two hops after you stop speaking for your contact to realize that you stopped. It takes two more hops for the contact to reach you. This is about 89,000 miles of transmission at about the speed of light. Thus, even if reaction time were zero, it would take about half a second for a response.


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Salmon Egg

Good memory.

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Distance for Geosynchronous Orbit Kepler's third law allows us to calculate the distance from the center of the Earth for a geosynchronous orbit. Kepler's third law is a mathematical equation relating the orbital period, orbital radius, and the mass of the Earth or other object being orbited. See the illustration for the mathematical details. Using Earth's rotational period in seconds and Earth's mass in kilograms gives a value of 42,200 kilometers (or 26,200 miles) for the distance a satellite has to be from the center of the Earth to orbit geosynchronously. Subtracting Earth's radius gives a distance from Earth's surface of 35,900 kilometers or 22,300 miles.

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Just from my expeeriences with my cell phone calling a "landline" in the same room suggests that much/most of the delay has to do with "digitizing."

I have taken two courses in which the instructor was on another campus. The total digital delay was long enough that you could turn around quickly as see the back of your head on the screen! (Hey, you gotta do something while waiting for the instructor to show up.)

Reply to
John Gilmer

It would perform better, but it doesn't offer the coverage that satellites do. Satellite links can be made to any point on Earth, so news organizations supply their remote reporters (even in the USA) with satellite terminals to establish links. Normally, it's faster and easier to set up the satellite link than a terrestrial link.

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Hope for the Heartless

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