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Science Forum

  1. 16 Feb '10 14:08
    Will somebody please explain this to me, as I can't wrap my arts degree brain around it. I am currently living in China, and recently made several phone calls back to the UK. Now my rudimentary knowledge of how telephones work tells me that the voice pattern is transmitted as an electrical pattern down the wire, most probably bounced off a satellite, and reproduced at the other end.
    How does this happen fast enough for there to be absolutely no delay in the conversation? Permit me to marvel at this, but I talked to people on the other side of the world as if they were in the same room! Surely even a light beam would take some time to go that distance?
  2. Standard member Palynka
    Upward Spiral
    16 Feb '10 14:23 / 1 edit
    If it went around the word, light could do about 7.5 laps around the Earth's equator in a second. Take that Usain Bolt!
  3. 16 Feb '10 14:24 / 1 edit
    Originally posted by Keeni Meeni
    Will somebody please explain this to me, as I can't wrap my arts degree brain around it. I am currently living in China, and recently made several phone calls back to the UK. Now my rudimentary knowledge of how telephones work tells me that the voice pattern is transmitted as an electrical pattern down the wire, most probably bounced off a satellite, and ...[text shortened]... they were in the same room! Surely even a light beam would take some time to go that distance?
    There is a short delay, but too short to be noticed. If the signal goes to a sattelite and back we have a delay of approx. .2 seconds. The computers are very quick coding and decoding your voice in real time.
  4. Standard member sonhouse
    Fast and Curious
    16 Feb '10 15:10
    Originally posted by FabianFnas
    There is a short delay, but too short to be noticed. If the signal goes to a sattelite and back we have a delay of approx. .2 seconds. The computers are very quick coding and decoding your voice in real time.
    In two tenths of a second the signal (as a radio wave) travels almost 38,000 miles which is why he said there is a 2/10ths second delay, that is the delay from the earth station to the satellite which is about 20,000 miles up in orbit and back down, about 40,000 miles round trip. There would be more delays where the signal travels on wires which is a lot slower but still not enough for you to detect.
    Where the speed of light comes into play is for astronauts on the way to the moon. If you look at the round trip distance, almost a half million miles, and light goes 186,000 miles per second or 300,000 kilometers per second, if someone on the moon talks to someone on Earth, the delay would be around two and a half seconds, call it three seconds. That you would notice.
  5. 16 Feb '10 15:28
    Originally posted by sonhouse
    In two tenths of a second the signal (as a radio wave) travels almost 38,000 miles which is why he said there is a 2/10ths second delay, that is the delay from the earth station to the satellite which is about 20,000 miles up in orbit and back down, about 40,000 miles round trip. There would be more delays where the signal travels on wires which is a lot sl ...[text shortened]... the delay would be around two and a half seconds, call it three seconds. That you would notice.
    I don't know about miles. It's 36,000 km to the geostationary orbit. 0.1(ish) seconds. There and return 0,2(ish), (or perhaps 0.3) seconds. According to my quick calculation.

    This delay I don't mind. The echo-effect you sometimes hear in the mobile thru intercontinental calls bothers me.
  6. 16 Feb '10 23:46
    Thanks for all the quick and useful replies!
    So Fabian, what causes the echo? I agree it's very annoying...
  7. Standard member sonhouse
    Fast and Curious
    17 Feb '10 02:48
    Originally posted by Keeni Meeni
    Thanks for all the quick and useful replies!
    So Fabian, what causes the echo? I agree it's very annoying...
    Here is one creepy explanation:

    http://onlinejournal.com/artman/publish/article_3678.shtml
  8. 17 Feb '10 05:49 / 1 edit
    Originally posted by Keeni Meeni
    Now my rudimentary knowledge of how telephones work tells me that the voice pattern is transmitted as an electrical pattern down the wire, most probably bounced off a satellite, and reproduced at the other end.
    Most exchanges are digital nowadays, so your voice is converted to digital at your local exchange and then sent via various means to the exchange nearest the person you are communicating with and converted back to analogue.
    I rather doubt that your calls go via satellite, they probably go via the same optic fiber networks that the internet runs on, so the main traveling is actually at light speed. You will probably find that a large part of any delays experienced are when the signal is being converted or transmitted through devices and so the delay has more to do with how many devices between you than the actual physical distance.
    In my experience with satellite, the delays are significantly larger than ground based optic fiber.

    Also, a delay of up to a second or so is not really noticeable when the call quality is good.

    If you are curious about the speed of communication, then try pinging servers around the world.
    I can ping Google from here in Cape town and get a reply (thats a two way trip to somewhere in the US) in a mere 350 milliseconds (thats 0.35 seconds). So I could make a voice call via the internet to the US with a one way delay of under 0.2 seconds.
  9. 17 Feb '10 08:26
    i can remember phone delay in calls placed to some countries. don't remember it recently but it's been a year or so since i've done it. maybe the delay i'm remembering is from early 90's.
  10. Standard member Palynka
    Upward Spiral
    17 Feb '10 10:41
    Originally posted by twhitehead
    Most exchanges are digital nowadays, so your voice is converted to digital at your local exchange and then sent via various means to the exchange nearest the person you are communicating with and converted back to analogue.
    I rather doubt that your calls go via satellite, they probably go via the same optic fiber networks that the internet runs on, so th ...[text shortened]... my experience with satellite, the delays are significantly larger than ground based optic fiber.
    Exactly, this is the main reason why delays seem much smaller now than 20 years ago.