[amsat-bb] The Moon is our Future / antennas

[G0MRF@aol.com]

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.


Hi all.
 
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.
 
Thanks
 
David  G0MRF