[amsat-bb] The Moon is our Future / antennas
G0MRF at aol.com
Fri Jul 3 16:21:08 PDT 2009
In a message dated 03/07/2009 20:46:44 GMT Standard Time,
kd6ozh at comcast.net writes:
Building a prototype that works on Earth for project like this is only a
few percent of the effort required. Treating it as a radio club project
won't be effective as people need to sign up for a 5-year project.
John is absolutely right in saying the complexity cannot be easily compared
to a terrestrial radio project. One other thing that stands an almost zero
chance of succeeding is a dish antenna that needs to point towards the
earth. If NASA and the ISS have trouble with moving parts on the solar array
you can imagine how much more difficult it would be on the moon.
However, how about this.
The problem with the higher bands is power generation / path loss / antenna
gain. Any higher band like 1.2, 2.4 or 5.8G would need a high gain antenna
to offset the increased path loss.
But, instead of a conventional steerable dish....with its unreliable moving
joints...How about an electrically steerable array of patches / dipoles /
or any other type of antenna element.
But how to 'point' it?
Well. actually I think Tom Clark provided the answer for that with his
proposal of a few years ago. The principle is this: If you have 2 arrays. One
say on 5.6G uplink and one on 5.8G downlink, then the receiving array can
electrically look in different directions for a signal from the Earth.
Once the receiver has identified a signal and optimised the RX Antenna, the
information on the direction of the Earth i.e. the direction of the strongest
incoming signal can be used to configure the transmit array which will
then beam a signal back to earth with high ERP.
Directional, high gain, and no moving parts.
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