[amsat-bb] Circular Antennas
bruninga at usna.edu
Sat Aug 13 16:49:56 UTC 2016
Noting wrong with "circulars". Whats wrong is expecting to hear a weak
signal on the horizon using no gain.
Eggbeaters are great antennas that give good circular polarization at all
elevation angles to cover the whole sky and are great for non-tracking
ground stations listening to strong signals from space (the ISS for
example). But by definition, you cannot hear "all of space above the
horizon" without giving up gain everywhere.
Space tracking satellites is not homogeneous. You need TEN times the gain
down near the horizon compared to overhead. Any antenna designed to hear
everywhere upwards equally is going to be ten times worse on the horizon
where it needs gain the most. And satellites spend more than 70% of their
time below something like 22 degrees.
Please see: http://aprs.org/LEO-tracking.html
On Fri, Aug 12, 2016 at 5:14 PM, Dave Mann <cwo4mann at comcast.net> wrote:
> My experience with the M2 eggbeaters left something to be desired. The
> 70cm antenna was deaf without a gasfet preamp. I use the 2m one as my
> local repeater and simplex antenna now.
> I've read other comments here about limitations, but I'm still not
> convinced circulars are a bad thing.
> That's about all the advice I can render.
> Sent from my iPad
> > On Aug 12, 2016, at 13:40, Gerald Payton <gp_ab5r at outlook.com> wrote:
> > Trying to get back into satellite radio from the early 2000s, I wonder
> what happened to circular helical antennas. Are they out of fashion now?
> > 73,
> > Jerry AB5R
> > EM12kh
> > _______________________________________________
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