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Re: S band and Eagle: an appeal for a higherleveldiscussion



It is a simple matter for a ground station to raise power and be heard above 
the din.  Most WiFi are at the milliWatt level.  It is hard for the 
satellite to raise power and be heard above the din.

I found AO-13 to be the opposite.  My original mode B (V) antenna was not 
large, and was not near the wind load or weight of my small dish.  Later I 
went to a larger Yagi, because I got "into" the ZRO tests.

A little simple math from the ZRO test.

Let's assume the downlink from the new bird will as good as AO-13 (I expect 
it will be better).
With a 12 foot yagi I made ZRO 9 which is 27dB below the recommended signal 
level for QSOs.
I will confess it was tough copy so I will give up another 3 dB just to be 
nice.
So my 12 foot yagi (homebrew, not computer optimized) had 24 dB to spare.
A six foot Yagi should have 21 dB to spare.
A three foot Yagi should have 18 dB to spare.

We are not talking about large antennas.  The Yagi does need proper care and 
feeding, but I never did smoke it by transmitting into it either.

Looking forward to mode B (U/V) again, 73,
Joe

----- Original Message ----- 
From: "Greg D." <ko6th_greg@hotmail.com>
To: <amsat-bb@amsat.org>
Sent: Sunday, September 10, 2006 1:40 PM
Subject: [amsat-bb] Re: S band and Eagle: an appeal for a higher 
leveldiscussion


> {Tilt}
>
> 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@mta.ca>
> Reply-To: brobertson@mta.ca
> To: amsat-bb@amsat.org
> Subject: [amsat-bb] S band and Eagle: an appeal for a higher level
> discussion
> 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
> VE9QRP
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>
> _______________________________________________
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