[amsat-bb] Homebrew Up-Dated Eggbeater Antenna (correction)

Tue Mar 15 20:11:08 UTC 2016

Although my comments are true, I had not looked at the "updated" web page:
http://wb5rmg.somenet.net/k5oe/Eggbeater_2.html

It appears he addressed all those issues and has an eggbeater design that
does address those same issues.  If that works, then that is the same thing
I was talking about and seems to be a good approach.  I'd love to see a
cookoff between the two antennas.  Bob...

-----Original Message-----
From: Robert Bruninga [mailto:bruninga at usna.edu]
Sent: Tuesday, March 15, 2016 1:32 PM
Subject: RE: [amsat-bb] Homebrew Up-Dated Eggbeater Antenna

My 2 cents:

The problem with Eggbeaters is that their design goal (omni coverage) sounds
good but also means, by definition, equally poor in all directions.
There is no such thing as "gain" for an omni.  The closer its gain
approaches 3D omni, in all directions, then the closer its gain approaches
0 dBi.  Of course, placed over a ground plane, then they can achieve 3
dBi...

Now, on the other hand, satellites are nowhere near omni located.  They are
10dB or more farther away on the horizon than when they are overhead.
So you don't need as much gain at all overhead as you need on the horizon.

Further, satellites spend more than 70% of all pass times below 22 degrees!
(where they are weak) and only 5% of their time above 45 degrees where they
are 10 dB stronger.

The last thing then that you need for "omni" coverage for a non-pointing
antenna, then, is gain that is UP (where the satellite is 10 times
stronger).

See the scale drawings of a LEO pass: http://aprs.org/LEO-tracking.html

BUT on the other hand, most cubesats simply do not have the power to close
the link to an OMNI antenna when it is on the horizon.  It just cannot
happen due to the distance and the omni only being at best 3 dB gain.

So the BEST "omni" in my opinion is a 19" whip over a large metal ground
plane.  Not only does it provide 5 dBi gain above 15 degrees or so on VHF,
it also provides almost 7 dBi gain on UHF above about 30 degrees where it
acts as a 3/4 wave vertical..

Yes, it has a null overhead, but the satellite is 10 times stronger then.
And the satleilte is only in that null less than 2% of all pass times.

So the 19" vertical gives good gain from above the horizon in all directions
and sacrificaes some gain overhead wehre it is not needed.  And no omni
antenna is going to  hear these weak satellites all the way down on the
horizon where they are 10 times weaker.

And a 19.25" vertical piece of wire over some chicken wire is pretty easy to
construct, AND it does not need to be on the top of a tower, since it cannot
hear to the horizon anyway.  So jjust put it where it can see most of the
sky above abouit 15 degrees and you will hear about all you can on an Omni.
And it is not bad...

The value of a true circular hemispherical antenna is only when the satelile
is strong (ISS) and it can be heard even on the horizon.  Then the circula
hemispherical antenna has the advantage of fewer nulls in its pattern.  But
you give up gain where it is most needed to get that.

And a low noise preamp is essential...

Just my 2 cents...
Bob, WB4APR

-----Original Message-----
From: AMSAT-BB [mailto:amsat-bb-bounces at amsat.org] On Behalf Of Paul
Stoetzer
Sent: Tuesday, March 15, 2016 1:12 PM
To: jim at k6ccc.org
Cc: amsat-bb at amsat.org
Subject: Re: [amsat-bb] Homebrew Up-Dated Eggbeater Antenna

Jim,

The key words here are "noise floor." Omnidirectional antennas can work for
satellites when you have a low noise floor and short runs of very good coax
(and/or a preamp).

As an example, I've listened for SO-50 a couple of times from here in
Washington, DC with my Baofeng UV-3R+ and Nagoya NA-774 telescopic whip. I
can hear the satellite a bit, but still quite nosily, above 45 degrees.
Back in August, I was in a field in the middle of nowhere and heard it very
well from 5-7 degrees above the horizon.

Another example is that some people report decent telemetry success from
AO-73 (when in high power mode) using nothing more than 1/4 wave whip.
I've never been able to decode a single packet with that type of setup here
in the city.

Most people live somewhere between the two extremes I've presented here of
"field in the middle of nowhere" and "apartment building in a major urban
center" so your mileage may vary. Just keep in mind that in any receiving
system, you are looking for an optimal signal to noise ratio. If you have no
noise, you don't need much signal and omnidirectional antennas might work
fine. If you have a ton of noise, you are going to need a lot of signal from
the satellite, which means a beam with decent gain.

73,

Paul, N8HM

On Tue, Mar 15, 2016 at 12:46 PM, Jim Walls <jim at k6ccc.org> wrote:
> I built one about a decade or so ago and was grossly underwhelmed with
it.
> I built it to use for a sat igate.  I was able to decode maybe one or
> two packets per day.  Everything else was lost in the noise floor..
> Only had about 20 feet of RG-214 cable to the receiver.
>
>  Jim - K6CCC
>
>
>
>
>
> ----------------------------------------
>  From: "Joe" <nss at mwt.net>
> Sent: Tuesday, March 15, 2016 9:37 AM
> To: "amsat-bb at amsat org" <amsat-bb at amsat.org>
> Subject: [amsat-bb] Homebrew Up-Dated Eggbeater Antenna Has anyone
> built this antenna, and what are your opinions? Meet all the claims
> being made?
>
> http://wb5rmg.somenet.net/k5oe/Eggbeater_2.html
>
> Joe WB9SBD
> --
> Sig
> The Original Rolling Ball Clock
> Idle Tyme
> Idle-Tyme.com
> http://www.idle-tyme.com
> _______________________________________________
> Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
> to all interested persons worldwide without requiring membership.
> Opinions expressed are solely those of the author, and do not reflect
> the official views of AMSAT-NA.
> Not an AMSAT-NA member? Join now to support the amateur satellite
program!
> Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
>
>
> _______________________________________________
> Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
> to all interested persons worldwide without requiring membership.
> Opinions expressed are solely those of the author, and do not reflect
the official views of AMSAT-NA.
> Not an AMSAT-NA member? Join now to support the amateur satellite
program!
> Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
_______________________________________________
Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available to all
interested persons worldwide without requiring membership. Opinions
expressed are solely those of the author, and do not reflect the official
views of AMSAT-NA.
Not an AMSAT-NA member? Join now to support the amateur satellite program!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb