[amsat-bb] Re: EggBeater

Robert Bruninga bruninga at usna.edu
Thu Apr 16 12:53:19 PDT 2009

> 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
>
>
>
> _______________________________________________
>
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of
> the author.
>