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Post by PhantomWolf on Jul 12, 2006 1:10:37 GMT -4
To stay in daylight your orbit would need to be 365.25 days.
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Post by gwiz on Jul 12, 2006 3:00:11 GMT -4
I need to read up on them, but wouldn't a variation of the "sun synchronous" orbit fill a 24/7 sunshine situation? IIRC, it's a slightly retrograde polar orbit that is designed to pass over the surface in identical lighting conditions orbit after orbit. Were this aligned with the Earth's terminator, it would possibly be a "sunshine" orbit.(?) Jarrah White wants a daylight orbit to stop the Apollo being visible to the naked eye, he doesn't want people to see that it's in low orbit. Unfortunately, Apollo in a terminator orbit is going to to be sunlit, but visible from places beyond the terminator in darkness, perfect satellite observing conditions. He also wants it to be below the Van Allan belts and perpetually visible form the moon.
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Post by PhantomWolf on Jul 12, 2006 4:42:14 GMT -4
Well if you put it in a 24 hour polar orbit (a real one, not a Jarrah White one [I wonder if he's related to Jack?}) then you could do that, except that you'd have to fly about for 8 days in the middle of the very thing he claims would have stopped them from flying through in a just a few hours........
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Post by gwiz on Jul 12, 2006 6:15:16 GMT -4
Question for Dwight as our resident communications expert:
Jarrah White thinks that Apollo stayed in low orbit, using LF communications that would be blocked by the ionosphere to relay signals via a lunar satellite. I was wondering what sort of frequency this would mean, and whether you could get the bandwidth for TV at LF.
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Post by colinr on Jul 13, 2006 7:51:42 GMT -4
Well I've taken a brave pill and registered over at Loose change - after 29 pages of semi incoherent ramblings , I thought I'd lend a hand to those upholding the truth re Apollo over there ...
My goodness Jarrad is a grumpy little soul isn't he .... some of the HB'ers seems a touch more rational - see you over there -
PS my first post was this morning....!
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Post by jaydeehess on Jul 14, 2006 0:11:49 GMT -4
Question for Dwight as our resident communications expert: Jarrah White thinks that Apollo stayed in low orbit, using LF communications that would be blocked by the ionosphere to relay signals via a lunar satellite. I was wondering what sort of frequency this would mean, and whether you could get the bandwidth for TV at LF. Analog TV uses 6 Mhz of bandwidth per channel though this includes a small guard band between channels. The video and audio carriers are separated by 4.5 Mhz IIRC the LF band is in the 100 Khz range so 6 Mhz of bandwidth is out of the question. You might be able to get by with a digital signal and slow scanning but this is supposed to be the 1970's technology , not 1990's or this century.
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Post by JayUtah on Jul 14, 2006 1:01:11 GMT -4
Crap, I actually knew that at one time but forgot. I haven't evangelized digital television in so long that I've forgotten the sermon.
6 MHz for analog TV is about right, and it corresponds to the channel widths in satellite television. Only there that same 6 MHz is an encoded digital transport stream with a capacity of about 30 megabits per second, encoded in a quadrature doohickey. You can cram about 6 acceptably-compressed standard resolution MPEG-2 video streams (and associated multiple AC-3 encoded audio streams) into that digital bandwidth.
The point is that digital television makes much more efficient use of the available bandwidth.
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Post by jaydeehess on Jul 14, 2006 1:28:42 GMT -4
Crap, I actually knew that at one time but forgot. I haven't evangelized digital television in so long that I've forgotten the sermon. 6 MHz for analog TV is about right, and it corresponds to the channel widths in satellite television. Only there that same 6 MHz is an encoded digital transport stream with a capacity of about 30 megabits per second, encoded in a quadrature doohickey. You can cram about 6 acceptably-compressed standard resolution MPEG-2 video streams (and associated multiple AC-3 encoded audio streams) into that digital bandwidth. The point is that digital television makes much more efficient use of the available bandwidth. IIRC, Our cable system's QAM (quadrature amplitude modulation) manages up to 8 SD channels per 6 MHz band. But cramming that much in can be problematic if there is a sudden demand that causes too much compression of the data. (ranting mode) Frankly I don't see a great advantage to digital or HD(IIRC only 2 HD channels per 6 Mhz ) other than better usage of available spectrum, especially for satellite transport. The 6 or 8 fold increase in traffic however did not make transport any cheaper for the end user, only more profitable for the satellite carrier.(that's me being cynical) HD looks great,,,,,,,,,until things start moving around a lot or there is too much randomness in the picture(a shot of a sunlit lake with small waves for eg.) when this happens it looks worse, IMHO, than analog. It is too hard for the system to compress and thus errors occur in the picture. I have also installed HD cable for some of our customers. Very often when they see that the majority of the stations are still 4:3 format and that this leaves a black bar on each side of their brand new HD ready monitor they ask for the set-up that exapnds this to full screen. ARRRGH,,,,,,,,,, why make all SD 4:3 pictures look like carp?? It boggles the mind. No, Oprah hasn't gotten heavy again, your TV is stretching her out sideways because you wanted it that way.
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Post by PhantomWolf on Jul 14, 2006 2:43:00 GMT -4
Very often when they see that the majority of the stations are still 4:3 format and that this leaves a black bar on each side of their brand new HD ready monitor they ask for the set-up that exapnds this to full screen.
My widescreen TV does that in Standard mode, but I usually use it in Natural mode. This simply expnds the image to fit widthwise and then chops a little bit of the top and bottom off, which usually doesn't matter.
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Post by hplasm on Jul 14, 2006 5:14:43 GMT -4
Question for Dwight as our resident communications expert: Jarrah White thinks that Apollo stayed in low orbit, using LF communications that would be blocked by the ionosphere to relay signals via a lunar satellite. I was wondering what sort of frequency this would mean, and whether you could get the bandwidth for TV at LF. At LF frequencies, (ie less than 100MHz), the ionospheric effects are dependent on many factors, such as solar activity, time of year and frequency. It is not, as our friend JW seems to think, opaque, and even one tv signal, taking up 6Mhz at these sorts of freqs would be detectable all over the world, even on the other side- due to reflection from the underside of the ionosphere- angle of incidence being another factor. Many people do long distance TV receiving for a hobby- DXTV. Perhaps he is thinking of the signals used for inter-satellite comms, used by the military, which uses a frequency band that is in the oxygen absorption band; and so can't pass down through the atmosphere- but as usual the facts are distorted...
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Post by ktesibios on Jul 14, 2006 14:05:19 GMT -4
IIRC the combination of reduced frame rate (10fps vs. 29.97 fps) and reduced resolution allowed the signal from the black and white camera used for Apollo 11 to take up only about 500 kHz of bandwidth.
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Post by JayUtah on Jul 14, 2006 17:19:37 GMT -4
That may be true. We have to keep in mind that these were not standard television signals.
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Post by JayUtah on Jul 14, 2006 17:45:19 GMT -4
IIRC, Our cable system's QAM (quadrature amplitude modulation) manages up to 8 SD channels per 6 MHz band.
Satellites use QPSK, a simpler modulation that is more tolerant of noisy carriers. QAM methods require a fairly high SNR but can cram quite a lot of data down a wire.
But cramming that much in can be problematic if there is a sudden demand that causes too much compression of the data.
The typical transport stream is built in a linear fashion. First the MPEG-2 required tables are put onto the wire at appropriate intervals, then each program's packetized elementary streams are added by individual stream injectors one after the other. The guy on the end may not have much headroom. The stream injectors (ca. $200,000 a pop) are pretty good at maintaining quality of service for their individual streams, but a rather poor job of optimizing the entire stream for overall quality. The guy at the end may be left with only 6 Mbps at any one second and so he'll just have to make the best use of it he can.
Providers try to mitigate this by arranging the services on streams according to their gross bitrate requirements. So a service like ESPN where charging quarterbacks and full-screen jiggling cheerleaders suggest (nay, demand) a high bitrate are teamed up with services like C-SPAN that require only the occasional transmission of moving lips.
ARRRGH,,,,,,,,,, why make all SD 4:3 pictures look like carp?? (emphasis added)
Because making them look like haddock or trout takes too much bandwidth. Either that or you're spending way too much time watching Sportsman's Challenge.
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Post by Joe Durnavich on Jul 14, 2006 20:23:27 GMT -4
At LF frequencies, (ie less than 100MHz), the ionospheric effects are dependent on many factors, such as solar activity, time of year and frequency.
...and the time of day, of course. The ionosphere is thinner at night and doesn't have much effect on signals above, oh, around 10 MHz, I'd say--somewhere between 7 MHz and 14 MHz, anyway.
A TV signal below 30 MHz that did penetrate the ionosphere (and it will somewhere as hplasm points out) would be instantly discovered because it would stomp on a lot of other traffic.
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Post by ktesibios on Jul 16, 2006 15:53:24 GMT -4
That may be true. We have to keep in mind that these were not standard television signals. Found it. The article "The Lunar Televison Camera" By E. L. Svensson in the March 1968 issue of Westinghouse Engineer (available here) says: "Since the camera must share bandwidth with voice, biomedical and other telemetry data, the camera is limited to a 500 kHz bandwidth." Table II in the same article specifies video bandwidth as 2Hz to 500 kHz. The block diagram given shows the last stage in the video signal path as "filter and line driver"; unfortunately this stage is not described in the text but it seems reasonable to think that the "filter" portion was a low-pass intended to keep out-of-band (>500 kHz) information out of the video output. The description of the unified S-band communication system here indicates that the video signal had a bandwidth of 10 Hz-500 kHz and frequency modulated the S-band carrier directly. I guess that finding ways to fit a usable though not hi-fidelity video signal into the bandwidth the designers of the USB system could allocate to it is an example of the "problem-solving within constraints" principle Jay has often spoken of.
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