[amsat-bb] Re: S band downlink on P3E

John Zaruba Jr aa2bn at comcast.net
Thu Sep 7 16:27:00 PDT 2006

While I'm also disappointed in the lack of a 2.4 GHz downlink, I  
think the rational laid out in the latest AMSAT Journal presents a  
reasonable analysis of the situation.

The few weeks I was able to use my S Band equipment (K5GNA  
downconverter + 60 cm dish + K3TZ design patch feed) AO40 never  
rendered what I would refer to as an ear drum popping signal, the  
best I ever achieved was around an S5.

Now, let me provide the disclaimer that I am not an engineer nor  
rocket scientist, but assuming the 17db increased noise floor  
reference in the Eagle Update article is correct, and the general  
convention that receiver S units are about 5 db, I believe that the  
best case signal I would hear at my location would be around an S2.  
Now from experience I've found that the best case signal represents a  
only a small part of the total pass visibility.

I also believe that it would be impractical to increase the  
satellite's transmitter output to make up for the increased  
terrestrial noise floor, given the power generation and payload  
constraints of the proposed Eagle design.

Since we (speaking as an AMSAT member) build very capable satellites  
on a shoe string budget (compared to commercial operators) I feel  
that every opportunity to advance the communications and aerospace  
state of the art must be taken, in view of the fact that launch  
vehicle availability is extremely limited for non-professional  
organizations. To my mind, the design team are making the best  
engineering decisions they can.


John AA2BN
AMSAT 22683 

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