[amsat-bb] Re: EggBeater

[Robert Bruninga]

> 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: 
www.aprs.org/rotator1.html

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.

Bob, WB4APR

 Then a higher elevation is closer so the path 
> loss is less.  Almost everyone that I know who started out 
> 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 at 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
(generally)
> 
> than a dipole made out of a piece of wire.  By definition,
these
> 
> 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 
> 
> > an Arrow. 
> 
> 
> 
> This is because the arrow is a "gain" antenna.  Gain means
that
> 
> the structure sacrifices gain in all directions to concentrate
> 
> it in only one direction.  Which then you have to point.  It
is
> 
> 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 my QTH.
> 
> 
> 
> Yes, by definition.  An omni cannot hear most of the amateur
> 
> satellites on the horizon, because there just isnt enough
signal
> 
> (except for ISS).  You need some gain to hear them on the
> 
> horizon.  BUT when the satellite gets above 20 to 30 degrees,
it
> 
> 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
use
> 
> 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
enough
> 
> 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
> 
> reversed...
> 
> 
> 
> 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 better, 
> 
> > down to 10 degrees elevation in some directions.
> 
> 
> 
> Yes, some satellites are stronger than others.  But most are
not
> 
> designed with the 10dB link margin they need to hit omni's
> 
> horizon to horizon.  Most cannot afford to waste that much
power
> 
> for the benefit of people with omni's.
> 
> 
> 
> Plenty of people corrrectly swear by their omni that it can
hear
> 
> 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
to
> 
> VO-52 and the signals sounded like 20 over S9...  But then 30
> 
> seconds later, they were down where I expected.  Looking at
the
> 
> track, it was almost directly overhead (and 10 dB) stronger
than
> 
> when it is a few minutes later.
> 
> 
> 
> Good luck
> 
> Bob, WB4APR
> 
> 
> 
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