RE: Fw: Stop Your Whining Already! Re: [amsat-bb] Satellite FIeld Day!

[Tony Langdon <tlangdon@xxxxxxxxxxxxxxxxxx>]

> FM transponders fundamentally only let one guy in at a time, and the 
> physics dictates that its the guy with the highest signal 
> level.  Even if 
> everyone were working with exactly the same EIRP, distance 
> differences 
> would still produce tremendous power level differences at the 
> satellite, 
> and at any given time one station would still have a 
> substantial signal 
> level advantage over another.

To a point, this is true.  Some people claim it's only 6dB difference.  A
rough mental calculation puts the difference at more like 13dB, or 20:1.
This is significant.  However, one can easily determine if someone is using
excessive power by monitoring the pass for long enough.  Except for people
on the edge of the footprint, the point of maximum advantage (read: minimum
path loss) follows the bird and everyone eventually gets a fair go.  If a
station dominates for most of a pass, then they are likely running more
power than everyone else. 

> FM transponders simply aren't designed to let a lot of people 
> communicate 
> at once.  Therefore, they aren't much good in an emergency, 
> and aren't easy 
> to use in a contest.  If you expected something else, you had 
> incorrect 
> expectations.

This is true, but good operator procedure (running modest power, and
listening first - a human version of the CSMA/CD technique used on Ethernet)
will maximise throughput.  And people, being more intelligent can back off
and say "go ahead" to the other station heard heterodyning on the satellite,
just to save a few more seconds of transponder time.

> You and others have been piling on complaining about "big 
> gun" stations, 
> claiming that they ran hugely excess power, but I contend 
> that you have no 
> way to determine how much power they were running, or to what 
> degree it was 
> in excess.  That's the nature of an FM transponder.

It is possible to get a (very) rough indication, as the path losses don't
vary by that much, compared to those involving terrestrial repeaters.

> I suggest that next field day you consider the nature of the 
> satellite you 
> are trying to use.  If you want to use a transponder that is 
> designed to be 
> shared by a large number of people, then choose a satellite 
> with a linear 
> transponder instead of an FM one.

Good point.  Linear transponders do lend themselves to more throughput, due
to the combination of wider bandwidth of the satellite (40-100 kHz, instead
of 25 kHz) and narrower bandwidths per QSO (2.5 kHz, much less if using CW
compared to 25 kHz).

> I also suggest that in a real emergency you need margin 
> against unforseen 
> circumstances and the bedlam created by the real emergency 
> and in a contest 
> you need margin against the bedlam created by competition.  
> In that sense, 
> the contest accurately simulates difficult emergency 
> conditions.  Sounds 
> like you just weren't up to the challenge.

One would also hope than in an emergency, there would be a control station
managing the traffic, and that control station would be the one with the
kilowatt and long Yagi, to ensure they maintain control.  Everyone else
should run a lower power.

> 
> Someone suggested a rule change to limit the number of points 
> one could get 
> on an FM satellite.  I think that's a reasonable idea.  Of 
> course, in a 
> real emergency, there won't be any such "rules".

Hmm, I'd hope there was some form of operating procedure (AKA rules) during
a real emergency, otherwise hams wouldn't be of much value in an emergency
either, when the bands descend into an uncontrollable rabble...
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