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Post by PeterB on Oct 5, 2005 0:51:01 GMT -4
Incidentally, I've done a little more research on Video Clip 2. At the start of the clip, it says something about GMT 198.1.30 or something like that. That means it's the 198th day of 1969, or 17 July. This was the second day of the Apollo 11 mission. Now, if you go to www.hq.nasa.gov/alsj/a11/AS11_TEC.PDF you'll find a massive (16 meg) PDF which contains the complete air-ground transcript for the mission. If you can open it, scroll down to the section around 1 day plus 9 or 10 hours into the mission, and you'll find the specific section of the mission which this video clip relates to. According to NASA, the spacecraft was 130,000 miles from Earth at the time. So I still don't really know what the clip is supposed to explain. It'd be good if you could explain this in more detail. Cheers
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Post by PeterB on Oct 9, 2005 22:38:23 GMT -4
Just a little bump for Margamatix...
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Post by PeterB on Nov 20, 2005 18:34:45 GMT -4
G'day Margamatix
Good to see you back here. (No need to make any comments about the Ashes or the Rugby Union, please.)
I was wondering whether you'd like to resume this discussion?
Cheers
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Post by margamatix on Nov 20, 2005 18:39:20 GMT -4
I would if I wasn't going to bed in 5 minutes but I'll try to get onto it next weekend, time permitting.
Meanwhile can I ask you if you remember transcontinental TV interviews from the 1960's with their long delays?
Gotta go now- trucks don't drive themselves!
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Post by PeterB on Nov 20, 2005 18:50:40 GMT -4
Margamatix said:
Okidoke. See you then.
Alas, no. I'm a bit too young for that. I was born in 1967. However, I suspect you're angling towards a point here, so I'm curious to know more.
Safe driving.
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Post by margamatix on Nov 25, 2005 16:31:12 GMT -4
Live interviews between London and New York during the 1960s had a delay of 2 to 3 seconds between transmission and arrival. This had the effect of making the recipient of the question seem a little "dim" as he/she still concentrated on the question long after the interviewer had finished asking it.
Given that the highest satellites in Earth orbit, orbit at 22,000 miles, then the furthest this signal could have travelled is 44,000 miles.
The moon is over five times as far away, yet the signal delay was far less than the delay between London and NY.
Why would this be?
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Post by gwiz on Nov 28, 2005 5:38:55 GMT -4
Sorry to but in. My memory tells me the lag on transatlantic interviews of the period was a lot less than that. Since you made the claim, perhaps you could provide the evidence?
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Post by PeterB on Nov 29, 2005 2:34:42 GMT -4
Margamatix said:
*sigh*
Well, you're gone from here now, Margamatix, so our discussion has turned silent at one end. But I'll still answer your question.
I dare say that you haven't seen too many Australians interviewed via satellite on UK television. But here in Australia, we often see people in the UK interviewed by satellite. That delay you describe still exists, and it can still cause confusion where Person A briefly pauses then continues, and Person B, thinking Person A has stopped, starts talking, and Person A doesn't realise for a couple of seconds that they're being spoken over.
It's just like occasionally happened on Apollo.
As for why the delay happens here on Earth, I don't know the details, but I understand it has as much to do with signal processing in the studios as the time it takes the signals to shoot out to the satellite and back to Earth.
Why the delay was less for Apollo is presumably based on how the signals were processed once they got back to Earth.
And with Margamatix's banning, we might as well open the thread up to everyone.
Thanks to everyone for respecting my request to keep the thread just between Margamatix and I. I'm sure there were a few people who were itching to post to it. One person asked me why I didn't just PM Margamatix. Well, I wanted the discussion to be public.
Cheers
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Post by PhantomWolf on Nov 29, 2005 6:01:58 GMT -4
Actually now that Marga's gone and so I'm assuming you won't mind, Peter, a lot of the delay is in the proceessing and passing of information between satelites. You get the same effect when talking to someone in England by phone (well when over here in NZ.) Of course the Astronauts didn't have to worry about this as the signal wasn't passed through a series of satellites, but was directed straight to the receiving dish and then sent via land line to Houston.
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Post by gwiz on Nov 29, 2005 8:13:23 GMT -4
I was thinking trans-Atlantic rather than to Australia or NZ with my memory of shorter delays. I suppose UK-Australia could easily go via more than one satellite, giving double the delay.
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Post by dwight on Nov 29, 2005 19:09:31 GMT -4
A video uplink downlink in TV can have delay introduced by several factors prior to the actual transmittzer. Firstly if a studio has no direct uplink it will need to relay the signal via either landline, microwave, or these days ATM digital lines to a facility that can uplink. The satellite itself will introduce delay, although as the GOES timing checks revealed that this delay is around 250 microseconds in a direct line of site non-hampered link. Factor in NTSC PAL conversion into this as well...another delay. Despite what Margamatix stated, the delays have not suddenly reduced with modern TX/RX devices. In my 20+ years in the industry I have actualy witness more delay in recent days due to MPEG encoding decoding. Cross atlantic downlinks tend to use PANAM sat as the main satellite. Australian European links will generally use AUSSAT, or one of the OPTUS sats, then bounce more than likely over Asia, and then via Astra or Eutalssat depending on what is needed.
just my 2 cents Dwight
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Post by JayUtah on Nov 29, 2005 19:57:46 GMT -4
Yes, MPEG encoding creates a bitstream that is often delayed or retained because it can be. Analog signals often degrade when stored or delayed. It is common to buffer digital signals for load-balancing reasons.
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Post by Retrograde on Nov 30, 2005 1:32:42 GMT -4
Yes, MPEG encoding creates a bitstream that is often delayed or retained because it can be. Analog signals often degrade when stored or delayed. It is common to buffer digital signals for load-balancing reasons. It's been a long time, but I seem to recall that the movement of signals through land-line networks took place at considerably less than the speed of light. That's just transmission of a raw digital signal, in addition to whatever delay occurs at the endpoints...
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Post by JayUtah on Nov 30, 2005 1:53:59 GMT -4
Right. When we refer to the speed of light, it is usually to the speed of light in a vacuum. That isn't the same as the speed of light through fiber optics, or the speed of an electrical impulse through copper.
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Post by Retrograde on Nov 30, 2005 2:51:56 GMT -4
Right. When we refer to the speed of light, it is usually to the speed of light in a vacuum. That isn't the same as the speed of light through fiber optics, or the speed of an electrical impulse through copper. Well, yes, but I'm referring to something different. Typically, a 3000km landline would not go through a 3000km long pair of copper wires or fiber. It would go through a good number of substantially shorter links, which are connected to each other with various types of multiplexing/demultiplexing equipment, which introduce delay. The delay introduced by the electronics at the ends of each of the short links is often the dominating factor, so if you measure the time it takes for a signal to get from A to B divided by the distance from A to B (well, actually the inverse of that) it will usually be much smaller than the speed of light, in a vacuum or through a medium. But it's been a bunch of years since I've dealt with these issues, maybe these days there is a lot more point-to-point networking. I'm not sure...
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