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

[Clayton Coleman W5PFG]

WB4APR's summary matches my personal assessment of eggbeaters, having 
tried them on LEO's myself for a period of test: Eggbeaters are mediocre 
at best for our LEO, amateur satellite fleet.

There are situations eggbeaters may have their place:

	1. A fixed installation, such as telemetry gathering, in which you 
absolutely can't afford risk of mechanical rotor failure.

	2. A backup to a directional array.

	3. The satellite has a very strong downlink.

Beyond that I can't recommend them for anyone. I learned, like Bob said 
below, that a 1/4 wave ground plane on 2m is as effective or better. 
I've copied thousands of telemetry frames with an inexpensive, SO-239 
chassis connector-based ground plane. This was in a very low-noise area 
with no obstructions. Keep the feedline as short as possible, use 
quality feedline, and consider use of RX preamplifier as necessary.

I will say this, people DO make contacts on eggbeaters. They also make 
contacts with mobile whips and rubber ducks. Some folks are more 
successful than others at this. On a regular basis I can quickly 
ascertain when the other station in QSO with me is on an eggbeater or omni.

Two major factors at play can make or break an eggbeater being useful:

	1. Terrain/obstructions. Eggbeaters in the middle of your forested 
backyard are a total waste. Can you put them on the roof if it clears 
the trees? Are you in the concrete jungle?

	2. RFI/noise. Eggbeaters are far more prone to local RFI than a 
directional antenna aimed at the satellite. I've seen some situations 
where an omni couldn't copy a single telemetry frame, yet a 2 element 
yagi was copying the telemetry in exactly the same observation point 
from horizon to horizon.

In summary, I would recommend building an eggbeater with scrap materials 
versus buying a commercial one, so that no tears are shed over lost 
money once it's tossed into the rubbish bin.

73,
Clayton
W5PFG

On 5/3/2019 16:32, Robert Bruninga via AMSAT-BB wrote:
> 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