On Sun, 23 Oct 2005 08:13:45 GMT, "Frank Dresser"
wrote:


"matt weber" wrote in message
.. .
On Sat, 22 Oct 2005 00:33:19 GMT, (Mark Zenier)
wrote:

[snip]

Before satellites the Defense Department was able to send several
teletype channels at at time, maritime mobile. That was with a big dish
and probably 10's of kilowatts. (The best description of using that
equipment, that I've seen, was in a description of the incident where the
USS Liberty, the radio intelligence ship, was attacked by the Israelis.
In the Atlantic Monthly about 10-15 years ago, as I remember).

Yes, but that wasn't moonbounce, it was tropo scatter. YOu can only
use Moonbounce when the moon is visible to both ends. Troposcatter
works just about anytime, anywhere. The change in permittivity at the
top of the toposphere will actually bounce a tiny portion of the
microwave signal back down quite reliably. You can get about 600
miles that way. But you need the sort of big dish, and tens of
kilowatts to do it reliably. Only the military could really afford to
use it.



The USS Liberty is said to have had moonbounce capability. The moonbounce
antenna is supposed to have been one of the distinctions seperating it from
the Egyptian ship the Isrealis said they thought they were attacking.

The large parabolic antenna in the picture, pointing straight up, seems to
be that moonbounce antenna.

http://www.history.navy.mil/photos/i...00/u123118.jpg

Frank Dresser

Having it pointed straight up is the standard stowed position. At lot
less load on the mounting that way. However it could just as easily be
a tropo scatter antenna, and tropo scatter has the advantage that the
moon doesn't have to visible at both ends of the path.

however it could also have used a communication satellite. I think
only Syncom III was in Geo Syncrhonos orbit at that time, however
there were a number of other sats in LEO and MEO (such as Telstar)
that could have been used, and they would come into view every few
hours and would be usable for 15-30 minutes at a time with a usable
bandwidht of a few MHZ. The Syncom III video wasn't so great, since it
was a 2 Mhz transponder IIRC, and analog Television is 6Mhz.

.. The first Telstar went up in 1962, and I would be indeed surprised
is several Military sats didn't have similar capabilities at that
time. In the fall of 1967 I remember a professor of Meteoroloby at the
University of Wisconsin telling me about a single UHF transponder they
had put on one of the Tiros weather sats in orbit that could be used
(and was used as a voice channel). The roof of the Meteorology
department at UW had a modest steerable corner reflector to use it..
As it was in LEO, it only took about 50 watts on each end.