[amsat-bb] Re: EggBeater

w7lrd@comcast.net w7lrd at comcast.net
Thu Apr 16 11:36:25 PDT 2009

adding to what Bob said
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.  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


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



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