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

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 =----

"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