[amsat-bb] revised P3D link budget spreadsheet available

[Franklin Antonio <antonio@xxxxxxxxxxxx>]

Well, publishing that P3D uplink link budget spreadsheet produced responses 
from various knowledgeable folk, containing good information.  I've updated 
the spreadsheet as a result.  Getting the best numbers for all the 
parameters and issues is an iterative process.

The new spreadsheet says that for the 1.2GHz uplink, I need 5 Watts thru a 
DEM 45el loop Yagi or 19 Watts thru a DEM 12dBiC helix.  (under a set of 
assumptions you can read about in the spreadsheet)

The new spreadsheet can be found at http://members.aol.com/n6nkf/

Among the pieces of new info:  DB2OS says the 2.4GHz P3D antenna has 21dBiC 
gain, not 18dBiC as the article on the amsat web page says.  I had assumed 
that the spacecraft antennas pointed at warm earth, so used 290K as the 
antenna temperature.  DB2OS suggested lower numbers, and when I calculated 
the fraction of the antenna pattern that is occupied by earth I immediately 
saw why.  The spacecraft antennas see a lot of cold sky, so the average 
temperature is substantially lower.  And so forth...

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