Re: [amsat-bb] antenna for low elevation vs. high elevation

[Jens Schmidt <j.schmidt@xxxxxxxxxxxxxxx>]

Hi Ed,
Maybe my clock is slowing down to go back to standard time,
and that is why I can't understand you, (babelfish needed).
IT1.5 says for 60.675N, (150W,guessing); UTC 16 March, MA105 - 13:--
20 deg. elevation, MA210? - 20:30 -> 6.5hr, Max elevation 38deg.
Elevation change at most 1deg./11minutes, azimuth change at most 2 -3
deg./11minutes.
OK, lets say you have a large parabolic dish, beam width 2deg.
Sure a standard, of the shelf, az/el rotator isn't going to cut the mustard,
you will with such an antenna need something fairly accurate, but if that is
accepted then you should have a nice easy time tracking the satellite.
I have not looked in detail at the changes at a perigee pass with the
satellite at say 350 km above the earth, but from memory, the changes
to both azimuth and elevation become much more and less smooth, I reckon
that it would be a whole lot harder to steer a 2deg. antenna at perigee with
the needed accuracy. (Won't even think about doppler yet).
Certainly this is only one pass, others will be worse, and others may be
better.
I don't know what the current plans for perigee/attitude/inclination
changes will do for the orbit, in terms of argument of perigee and
orbital period, that will be interesting.
>From the original link budget, I think some thing like a 60cm dish was
recommended. Well, with the current alon/alat, that is likely not enough
at apogee. When the three axis stabilisation comes in, the smaller antenna
should be feasible, larger beamwidth available, less critical steering.
The power budget for a GTO orbit is another story, but might be
manageable with a small amount of offpointing around perigee.
OK, how wrong am I ?
73 Jens    ZL2TJT


"Edward R. Cole" wrote:

> Hmm...
>
> So at 60.675N lattitude I should just throw all my satellite equipment into
> the dumpster, right?  Well, I checked the next AO-40 pass and I get a max
> elevation of 29 degrees a little after perigee [2.5 hour pass].  Track
> AO-40 at apogee...forget it.  At the current inclination I'll never see the
> bird at apogee.
>
> So I can only hope that a more favorable antenna orientation will be
> obtained thru magnetorquing, so that perigee passes are accessible.  Looks
> like big antennas for the arctic!  That 8-foot dish may be needed afterall.
>  Maybe I can borrow Jodrell Bank!  ;-)
>
> Ed
>

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