Somewhere I read where the percentages of where
the satellites are in elevation. The majority of
low elevation is fairly high. Whereas as a
elevation of 70 plus degrees is quite low.
I have a table on my web page:
And looking at the figure it is obvious what we are saying.
Also there is a plot of a modest 6 element beam tilted up at 15
degrees (NO MORE!) showing how it and a TV rotator are all you
need to work all these LEO birds.
Then a higher elevation is closer so the path
loss is less. Almost everyone that I know who started
with a egg beater eventually gets a beam of some sort. So
why not start there? A simple short beam aimed at about 30
degrees will cover a huge amount of sky
73 Bob W7LRD
----- Original Message -----
From: Robert Bruninga
To: billdz geo , amsat-bb(a)amsat.org
Sent: Thu, 16 Apr 2009 17:36:45 +0000 (UTC)
Subject: [amsat-bb] Re: EggBeater
I have both a commercial and a homebrew Eggbeater
and am disappointed with both,
Yes, because the best omni in the world is no better
than a dipole made out of a piece of wire. By definition,
antennas are OMNI's so they can hear in all directions. This
means they have zero gain. That is the basic law of physics.
... performance is far less than with an HT and
This is because the arrow is a "gain" antenna. Gain means
the structure sacrifices gain in all directions to concentrate
it in only one direction. Which then you have to point. It
impossible to have both gain and omni at the same time.
But what about Gain Vertical OMNI antennas? Well, they have
GAIN in all directions but only on the horizon. To get that
gain on the horizon, they MUST sacrifice gain somewhere else.
They sacrifice all gain that is UP. But that is where
satellites are, so it makes little sense to try to use one of
these, because you still wont hear any satelites, because the
gain you get "on the horizon" (maybe 3 to 6 dB or so) is just
barely enough, but then as the satellite gets higher, it gets
into the null of the antenna.
Guess an omni can't cut it, at least not from
Yes, by definition. An omni cannot hear most of the amateur
satellites on the horizon, because there just isnt enough
(except for ISS). You need some gain to hear them on the
horizon. BUT when the satellite gets above 20 to 30 degrees,
can be TEN times stronger and then ANY omni antenna will work
quite well (and you don't have to point it).
BUT... plot the amount of time a satellite is in view above 25
degrees and it is less than 1/4th of the time.
So there is no free lunch. Either put up an omni and only be
able to hear the satellites for on the order of 25% or less of
their available time in view (but have no moving parts). Or
a beam to get the gain on the horizon where you need it most,
and plan on keeping it pointed at the satellite.
Maybe if I could get it up higher, clear of all
roofs, it would do better.
Not really. Because getting "high" only gets you visiblity to
the horizon where, by definition, you already do not have
gain to hear any of the low powered satellites.
I can make contacts at relatively high sat
elevations, but can do just as well with a
$10 dual band ground plane.
Yes! That is exactly what we are talking about here. You
cannot have both. If you want an omni, then a simple ground
plane antenna made out of a few pieces of wire will do just
about as good most of the time as the most expensive "omni"...
Some will argue that you need circular polarization, to
eliminate some fading, but again you can also say that many
times the polarization is opposite and so even the right hand
circular antnena hears fades too when the circularity gets
Go with a simple 1/4 wave ground plane antenna with a preamp,
and hear well, less than 1/3rd of the time. Or us a beam...
My friend has an Eggbeater and the same preamp
at a clearer QTH, and he hears substantially
down to 10 degrees elevation in some directions.
Yes, some satellites are stronger than others. But most are
designed with the 10dB link margin they need to hit omni's
horizon to horizon. Most cannot afford to waste that much
for the benefit of people with omni's.
Plenty of people corrrectly swear by their omni that it can
very well. And tthis is true, but not at low elevations -and-
with the low power satellites. So always make sure you are
comparing apples and apples.
I was shocked during a class today when I went out to listen
VO-52 and the signals sounded like 20 over S9... But then 30
seconds later, they were down where I expected. Looking at
track, it was almost directly overhead (and 10 dB) stronger
when it is a few minutes later.
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