[amsat-bb] Re: S band and Eagle: an appeal for a higher level discussion

Greg D. ko6th_greg at hotmail.com
Sun Sep 10 11:40:56 PDT 2006


If 2.4 ghz pollution is going to be a problem for stations on the ground who 
are looking up (and away from) the noise, how is it possible that a 
satellite in the sky looking down on half of a planet's worth of 2.4 ghz 
noise, is going to be able to pick out one earthly station over the din?  
This is totally backwards in my mind.

Please, mode VS or US makes sense for the "installed base".  Mode B suffers 
from a worse problem than the S-band noise:  physics.  The Mode B receive 
antennas need to be phyiscally large, and putting up large antennas is 
becomming a problem more rapidly than overcoming noise on 2.4.  Small lots, 
CC&Rs, and other "environmental" factors are forcing hams to make do with 
smaller, less obtrusive antennas.  I can solve the small antenna uplink 
problem on V with a power amp; I cannot solve the problem of a small antenna 
downlink problem on V, even with a preamp.  I tried that when AO-13 was 
still up, and managed to get *one* contact.  Really, I should be running LS. 
  That would force me to get on 1.2 ghz.

Plus, noise on V is also getting worse by the day.  For years I have checked 
into a weekly SSB net on 2m (144.250 8pm local on Sundays) and have noticed 
there has been a huge increase in noise coming from the populated areas.  
Like Bill, I live in the Sierra Foothills (Auburn for me), and overlook the 
Sacramento Valley.  The noise peak from the direction of Stockton & 
Sacramento is amazing.  2.4 may be getting worse, but 2m noise is getting 
worse faster, and at least the laws of physics allow us to create S-band 
receive systems that can aim around (over) the din.

Greg  KO6TH

----Original Message Follows----
From: Bruce Robertson <broberts at mta.ca>
Reply-To: brobertson at mta.ca
To: amsat-bb at amsat.org
Subject: [amsat-bb] S band and Eagle: an appeal for a higher level 
Date: Thu,  7 Sep 2006 19:06:17 -0300

There has been a recent restatement of disappointment regarding the Eagle
design committee's recent choice to use S band as an uplink not a downlink.
Note that the next two HEO's scheduled to launch *will* have S band
downlinks, so there's no worry that people like I, who live in radio quiet
areas, will be unable to use our developing S band equipment in the future.

As I understand it, the Eagle design team have used standard predictions of
801.11 usage to determine mathematically that by the time of launch the
radio environment will simply not support reliable communications. I cannot
imagine that they like these conclusions. Implementing new bands entails
new risks, after all. But numbers don't lie (or shouldn't), and it would be
a horrible disservice to all of us if they designed and launched a bird
that was effectively mute at launch.

The design team have said again and again on this list that they would
welcome contradicting evidence that is cogent, and I, for one, believe
them. They're our volunteers, and they deserve our support. I can't provide
that contradicting evidence: I'm not skilled or qualified. But I can assess
an argument, and the responses so far have not been nearly as rigorous.
They have amounted to "works for me", which I think misses the point.

Please, please, those of you who are qualified and competent and hold the
opposing opinion, take the design committee at their word and assess their
work, check their assumptions, present cogent opposing arguments. There is
some thought that a dish antenna properly implemented will overcome the
obstacles described by the design team. Let's model this. Or those who live
in heavy 802.11b environments, do some experiements with terrestrial links
(which I suppose could be assumed worse than earth/sky). Who knows? Maybe
it's all like my last tax return, where a missed decimal point made me
think I'd have to take out a second mortgage to pay our taxes :-) This list
and the wiki exist so that we can undertake that sort of dialogue, and for
my part, it is my favorite part of participation in AMSAT.

Some have suggested that Eagle fly with an S-band downlink on the off
chance that it *does* work despite the theory; others, that we survey the
members to see what they'd like. I fully support the design teams rejection
of the former approach. Launch weight is very expensive and the kitchen
sink approach is not to my mind sensible. As to the latter, a survey
presumably pertains only to *working* bands, not ones that are polluted out
of existance.

It's human nature for us more readily to see our misfortunes as caused by
the malace of others, but I think we should strongly avoid terms like "bait
and switch". We'll get much further if we all assume the goodwill of
everyone involved.

73, Bruce
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