[amsat-bb] ARRL Antenna book, eggbeater antenna designs (not)

[Robert Bruninga]

Eggbeaters are ideal antennas for omnidirectional coverage with dual
polarization for strong signals with minimum fades....

But like any antenna, to get gain somewhere, you have to give up gain
elsewhere.  Here are all the issues and my opinions.

1) Satellites on the horizon are 10 dB farther away than ones above 22
degrees (2000 miles vs 700 miles).
2) Splitting gain into circular polarization (Eggbeaters) loses 3 dB
compared to incoming linear polarization
3) Small sats usually have linear antennas or, if they have cross
polarization then even if they are RHCP when approaching, they may be LHCP
going away, thus you still have a 50/50 chance of having a polarization
mismatch, though having both polarizations will minimize most fades.
4) Most small Amateur sateliltes have less than 1W transmitters and simply
cannot be heard on the horizon without several dB gain.

My Conslusions are:
1) An Egg beater is ideal for STRONG satellites (Think ISS with 10 Watts).
It will minimize fades horizon to horizon.
2) But there are NO, NONE, NADA current amateur satellites (not even the
ISS right now) at that power level.
4) Hence an eggbeater even with a dB or so gain on the  horizon simply is
not going to hear anything until the satellite gets above about 20 degrees
(when it is 10 dB closer)
5) So, why even bother with an eggbeater.
6) Use a simple 19.5" quarter wave vertical over a ground plane (for 2m).
It will have 5 dBi gain above about 15 degrees (several dB better than an
eggbeater).
7) and it will ALSO WORK even better as a 7 dBi gain UHF antenna (3/4 wave
vertical) above about 25 degrees up to 70 degrees (6 dB better than an
Eggbeater)...

AND it is DUAL band as well! (on the same coax!)

BUT, what about the donut hole overhead for these vertical antennas?

Forgetaboutit.!....  The satellite is only above 70 degrees about 1% of
the total pass times per day!  And then for less than about 30 seconds!

To visualize the orbit actual geometry see the scale plot on:
http://aprs.org/LEO-tracking.html

So, in my humble opinion, a 19.5" vertical whip antenna in the middle of a
car roof (neat ground plane) will give pretty good satellite coverage.  It
will have some fades due to only one polarization, but the strong part of
the cycle will be 3 dB stronger than it would be on a dual polarizatiaon
antenna.  And you don't have to be parked on a mountain.  Since again, no
omni antenna can hear these weak satellites on the horizon anyway, so as
long as the trees are far enough away to give you sky above about 20
degrees, you will have about the best coverage you can get for about a 20"
of copper wire and a nice ground plane..

In my opinion anyway.

AND***  If you want to hear them all the way horizon to horizon, buy a $65
TV rotator and attach a small 5 to 6 element beam tilted up at about 15
degrees and hear them all!  See above web page...

Bob, Wb4APR

-----Original Message-----
From: AMSAT-BB <amsat-bb-bounces at amsat.org> On Behalf Of Devin L. Ganger
via AMSAT-BB
Sent: Friday, May 3, 2019 4:19 PM
To: AMSAT-BB at amsat.org
Subject: [amsat-bb] ARRL Antenna book, eggbeater antenna designs

Greetings, programs!

I'm looking to work with my son (who will be studying to get his
Technician license later this month) on building a UHF/VHF pair of
eggbeater antennas. I've found a few papers online, but does anyone have a
good reference to a detailed design?

Does the ARRL Antenna book latest edition have any significant coverage of
eggbeaters at all? I have an older version that has nothing.

Also, most of the designs I see are for a single band. If you're deploying
a pair for satellite operations, do you simply attach them through a
duplexer? I have a Diamond MX-72N that I picked up a while ago for using
with dual Baofengs, but it's been sitting in my drawer since I picked up
my TH-D72A. It has a 1.6~150MHz lead and a 350~460MHz lead.

Thanks in advance for any pointers you might have.


--
Devin L. Ganger (WA7DLG)
email: devin at thecabal.org<mailto:devin at thecabal.org>
web: Devin on Earth<http://www.devinonearth.com/>
cell: +1 425.239.2575

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