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Beaming shortwave from satellite/space
Wouldn't that provide a better coverage with less fading compared to
traditional approach? Or is it that shortwave needs ionosphere to work at all? Thanks. |
"Jim" wrote in message om... Wouldn't that provide a better coverage with less fading compared to traditional approach? Or is it that shortwave needs ionosphere to work at all? Thanks. Seems to me that the signal would have a pretty difficult time penetrating the ionosphere at HF frequencies.There are of course complications to that answer, such as MUF and incident angle, but in general if the ionosphere acts to reflect earth originated signals, it will do the same to space originated signals. Dale W4OP |
Jim wrote:
Wouldn't that provide a better coverage with less fading compared to traditional approach? Or is it that shortwave needs ionosphere to work at all? Thanks. When you transmit a shortwave signal from an earth-bound transmitter, it gets "bounced" off the ionosphere to come back down to the listener a few thousand miles away. If you were to transmit such a signal from space, it would bounce in pretty much the same way -- except that instead of bouncing down to a listener on Earth, it would bounce back out into space. Not particularly useful. -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com |
On Mon, 16 May 2005 02:01:18 +0000, Doug Smith W9WI wrote:
When you transmit a shortwave signal from an earth-bound transmitter, it gets "bounced" off the ionosphere to come back down to the listener a few thousand miles away. If you were to transmit such a signal from space, it would bounce in pretty much the same way -- except that instead of bouncing down to a listener on Earth, it would bounce back out into space. Not particularly useful. Nonsense (at least above the MUF). Consider QSOs made using Mode K (21 MHz uplink, 29 MHz downlink) of the RS-10/11 and RS-12/13 ham satellites. ===== RS-12 RADIO SPORT RS-12 Catalog number: 21089 Launched: February 5, 1991 Uplink: 21.210 to 21.250 MHz CW/USB Downlink: 29.410 to 29.450 MHz CW/USB Beacon: 29.408 MHz Robot: 29.454 MHz [05232004] ===== |
Snowbat wrote: On Mon, 16 May 2005 02:01:18 +0000, Doug Smith W9WI wrote: When you transmit a shortwave signal from an earth-bound transmitter, it gets "bounced" off the ionosphere to come back down to the listener a few thousand miles away. If you were to transmit such a signal from space, it would bounce in pretty much the same way -- except that instead of bouncing down to a listener on Earth, it would bounce back out into space. Not particularly useful. Nonsense (at least above the MUF). Consider QSOs made using Mode K (21 MHz uplink, 29 MHz downlink) of the RS-10/11 and RS-12/13 ham satellites. I recall listening to a satellite launched by China that played 'The East is Red' as it came within range. Don't recall the frequency right off hand but think it was up near 20 MHz or so. Perhaps someone else remembers it. dxAce Michigan USA |
dxAce wrote: Snowbat wrote: On Mon, 16 May 2005 02:01:18 +0000, Doug Smith W9WI wrote: When you transmit a shortwave signal from an earth-bound transmitter, it gets "bounced" off the ionosphere to come back down to the listener a few thousand miles away. If you were to transmit such a signal from space, it would bounce in pretty much the same way -- except that instead of bouncing down to a listener on Earth, it would bounce back out into space. Not particularly useful. Nonsense (at least above the MUF). Consider QSOs made using Mode K (21 MHz uplink, 29 MHz downlink) of the RS-10/11 and RS-12/13 ham satellites. I recall listening to a satellite launched by China that played 'The East is Red' as it came within range. Don't recall the frequency right off hand but think it was up near 20 MHz or so. Perhaps someone else remembers it. I did a quick Google and did find that that particular satellite was launched on April 24, 1970 and used 20.009 Mhz to broadcast 'The East is Red'. dxAce Michigan USA |
On Mon, 16 May 2005 01:51:02 -0400, dxAce wrote:
I recall listening to a satellite launched by China that played 'The East is Red' as it came within range. Don't recall the frequency right off hand but think it was up near 20 MHz or so. Perhaps someone else remembers it. CHINA-1 and CHINA-2 seem to fit your description: http://www.svengrahn.pp.se/histind/China12/China12.htm |
Snowbat wrote: On Mon, 16 May 2005 01:51:02 -0400, dxAce wrote: I recall listening to a satellite launched by China that played 'The East is Red' as it came within range. Don't recall the frequency right off hand but think it was up near 20 MHz or so. Perhaps someone else remembers it. CHINA-1 and CHINA-2 seem to fit your description: http://www.svengrahn.pp.se/histind/China12/China12.htm I'll have to get a sound-card going again here as it would be a thrill to listen to the recording they have up there on the site. Almost as much of a thrill as it was to hear it live at the time I'll bet. dxAce Michigan USA |
Snowbat wrote:
On Mon, 16 May 2005 02:01:18 +0000, Doug Smith W9WI wrote: If you were to transmit such a signal from space, it would bounce in pretty much the same way -- except that instead of bouncing down to a listener on Earth, it would bounce back out into space. Not particularly useful. Nonsense (at least above the MUF). Consider QSOs made using Mode K (21 MHz uplink, 29 MHz downlink) of the RS-10/11 and RS-12/13 ham satellites. I don't think that's what the OP was asking though. Heck, we already make massive use of frequencies above the MUF for this kind of service. Frequencies *way* above the MUF, as in above 1GHz. Really, it would make little sense to use shortwave frequencies above the MUF for routine service from space. The MUF changes -- a frequency that won't bounce back into space today might bounce tomorrow. It makes far more sense to select a frequency that's above the highest recorded E and F-layer MUFs (i.e. at least 250MHz) and not have to worry about it. (I wonder - but don't have the science to back it up - whether the MUF might be considerably higher for transmissions originating in space? Because they're striking the ionosphere at a shallower angle?) -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com |
Not necessarily. The planet Jupiter emits a signal that can be heard at
about 15 meter wavelength, about 21 mhz or so. That signal penetrates the ionosphere pretty nicely. See http://radiojove.gsfc.nasa.gov/libra...discovery.html for more info... bill KC9CS "Doug Smith W9WI" wrote in message ... Jim wrote: Wouldn't that provide a better coverage with less fading compared to traditional approach? Or is it that shortwave needs ionosphere to work at all? Thanks. When you transmit a shortwave signal from an earth-bound transmitter, it gets "bounced" off the ionosphere to come back down to the listener a few thousand miles away. If you were to transmit such a signal from space, it would bounce in pretty much the same way -- except that instead of bouncing down to a listener on Earth, it would bounce back out into space. Not particularly useful. -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com |
The ionosphere isn't anything like a perfect mirror.
RF at or below the MUF still penetrates, some fo it refracts. A friend just received her PHD in astrondomy and her thesis was based on observations on the 2 HF radio astronomy allocations. Even with the MUF right above either of these 2 freqs, signals stll penetrated the ionosphere. I will ask Ms C how mcuh attenuation there was. From conversations, it wasn't as much as I thought. It seems that even at best, less then 10% of the RF refracts in the ionosphere, the rest "punches" through. Terry |
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Bill Otten wrote:
Not necessarily. The planet Jupiter emits a signal that can be heard at about 15 meter wavelength, about 21 mhz or so. That signal penetrates the ionosphere pretty nicely. See http://radiojove.gsfc.nasa.gov/libra...discovery.html for more info... bill KC9CS Receiving the 21-Mhz HF (shortwave) energy from Jupiter depends on it's altitude above the observer's local horizon and the MUF (maximum usable frequency) for the particular area of the ionosphere where the signal is trying to penetrate to the ground. In the first case, when Jupiter is near the horizon, it's radio signal may not penetrate the ionosphere because of the shallow incident angle. The energy is refracted off the top of the ionosphere back into space like skipping a stone on water. In the second case, if the local MUF is too high, it won't allow the 21-Mhz energy to penetrate to the ground from space regardless of the incident angle. The best time to radio observe Jupiter is when the conditions are the opposite of the first two cases above, or particularly when it's high in the sky at night. This is when the signal passes through the ionosphere at a more vertical angle to the observer (no skipping) and the local MUF is at it's lowest for the day, which happens some time after sunset. It's also best when the solar flux is low, near sunspot minimum, as it is now. This insures a low MUF (well below 21-Mhz) so Jupiter's signal can reach the surface of the earth more often. ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
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Telamon wrote:
Looks like we are going to have to read up on this Terry. I've got a book I have not read yet called "Radio Frequency Principles and applications" that may shed some light on this. I'll let you know. -- Telamon Ventura, California -------------------------------------------- I went through my technical library last night with no success. Our friend Ms. C. will be comming through Lexington Sunday afternoon, to pick up her AOR7030+, and I will see if I loaned the book to her. As a rule, I don't loan books, too easy to lose them, if you want to read one, be prepared to read it here, or go with me to a photocopy machine and copy it. Terry |
"Jim" wrote in message om... Wouldn't that provide a better coverage with less fading compared to traditional approach? Or is it that shortwave needs ionosphere to work at all? Thanks. Aside from the propagation issues, the usual antenna for satellite work is highly directional. Antenna size is proportional to wavelength and SW wavelengths are a hundred times or so bigger than the usual satellite wavelength. Frank Dresser |
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