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

[Tony Langdon <tlangdon@xxxxxxxxxxxxxxxxxx>]

> If I am running 100 Watts to 22 elements to the bird and it 
> is at a LOW
> angle pass for me while you are running 5 watts to 3 elements 
> and it is
> directly overhead for you, YOU MIGHT BE THE BIGGER STATION!!!  Guys,

It would want to be a low pass - a very low pass.  Let's take UO-14 as an
example.  Ignoring attitude effects for now (i.e. assume the satellite
radiates isotropically).

The closest approach (TCA on 90 degree pass) is 800km
Range at AOS/LOS is around 3200 km.

Assuming inverse square law, the difference in path losses between overhead
and horizon is approx:

Square(3200/800), or 16.  In other words, around 12 dB (OK, let's make it 13
for a nice neat number).

Now, if I can work UO-14 with an EIRP of 200 mW (estimated minimum, lowest I
can go is around 600 mW which gives full quieting) when it's overhead, then
one would expect I need around 20 times that power at AOS or LOS, or 4W
EIRP.  This is borne out by experience, where I can still make a dent in the
Asian QRM with this kind of EIRP when the bird is low to the north.

If one wanted to ensure a reliable link, then you could add perhaps 10dB to
cover the effects of poor attitude, and maybe a little more if your QTH is
surrounded by trees, hills, etc.  I very much doubt you get to the 100W into
22 element stage, unless you're trying to work _below_ horizon grazing
passes, where the path may have a troppo scatter component.

Sometimes, SO-35 needs a little extra power when the attitude isn't
favourable for the 70cm uplink.  I haven't seen this issue on UO-14 in
practice, at this stage.

> understand that working a satellite is NOT a linear thing.  
> People with
> overhead passes are far more able to work the bird better 
> than those who
> have low angle passes.  It's the difference of the satellite 

Only to a point.  I've still made quite a noise running QRP to low passes.
:)

> being a few
> hundred miles away vs a few thousand!

Well, in miles, the difference is approx 500 to 2000, or only 4:1 (actually,
it's slightly greater, but not by much).

> Also, regarding DX pileups, the biggest guy doesn't always win.  I've
> managed to prove that.  I've also been a big guy and worked 
> the DX first.
> In fact, once the DX works the "few" big guys (and believe 
> me, the number of
> guys with 100 W and a dipole is FAR more than the big guns) 
> then we get out
> of the way and let everyone else slug it out.  It's called patience.

Terrestrial DX also has a lot more variables.  I used to come up high in the
pecking order on 15 metres when I lived out in the sticks.  My gear was an
FT7 (running about 15W) and a random length of wire strung up in the trees.
But with that very modest setup, I was still able to get in over the top of
the bigger stations from around the area.  The secret turned out to be that
I was in a particularly favourable location, with the right soil
conductivity and a little elevation running in my favour.

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