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

Fri May 3 22:24:01 UTC 2019

Hello Space Communicators!

Here are some observations about Satellite APRS on 145.825 MHz.

1) Receiving is harder than Transmitting.
2) Location is critical, avoid hill tops or parking structures in a city.

As far as Satellite APRS on 145.825 MHz with an Eggbeater, here are some
reference points.

My Dad (N6DAN) operates the #1 iGate in the world based on packets received
on 145.825 MHz. So, I think that documented track record carries a great
deal of merit and credibility. Having said that, he operates two radios,
one connected to the EBB144 and another to a directional antenna.

Egg Beater success pivots on two factors:

1) Pre-amp: the EBB is dull and needs help.
2) Noise: the EBB is useless in the city on a high pole, but perfect in
rural areas on a high pole. In the city the EBB works best below a wood
fence line.

W0ARP operates the #8 iGate in the world based on packets received on
145.825 MHz. He is only running the EBB144 with a pre-amp in a rural area.

Eggbeaters can be useful.

73s

Robert MacHale
KE6BLR Ham Radio License
http://spaceCommunicator.club <http://spacecommunicator.club/>
Supporting Boy Scout Merit Badges in Radio and Space Exploration

On Fri, May 3, 2019 at 2:49 PM Robert Bruninga via AMSAT-BB <
amsat-bb at amsat.org> 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
>
> -----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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> _______________________________________________
> 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!
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