[amsat-bb] Homebrew Up-Dated Eggbeater Antenna (make 100 ohm line)

Wed Mar 16 02:08:18 UTC 2016

> Main problem seems to be the 93 ohm coax,,,

But one only needs 13" of the 100 ohm line at VHF and only 4.5" at UHF so
just make it.
Cut a piece of RG59 say 40% longer than the right length.
Strip off the outer jacket and also slide off the shield.
Now cut the dialectric and center conductor to the right length.

NoW, then slide on enough heatshrink or wrap the dialectric with enough
electrical tape to build up the diameter of the dialectric with something to
bulk up the diameter until you get the right center to outer ratio to be 100
ohms.

Then slide the shield back over it, heat shrink the whole thing, and you
just made yourself a piece of 100 ohm coax, or any other impedance you want.

Have I ever done this? No.  But it should work if you can get the expanded
diameter right, and what you stuff it with has a reasonable diaelectric
constant.

At least it would be fun to take the challenge.

Or if you are very lucky, there may be a piece of larger 50 ohm line that if
you could slide out the center conductor and slide in a smaller one of the
right diameter you could do it that way too.

Hey, it’s a hobby...  of course you would need a dipper or antenna analyzer
to test it.  Just put a 200 ohm resistor on the end and see how close you
get to 1.0 SWR.

The more I think about it the more likely it would be to find some cheap
RG59 that the center conductor slides out of.  It has happened to me enough
times when I try to strip some cheap junk that the center conductor pulls
right out of short coax pieces...  Then just stuff back in a smaller center
conductor.

Maybe?
Bob, WB4APR

-----Original Message-----
From: AMSAT-BB [mailto:amsat-bb-bounces at amsat.org] On Behalf Of Douglas
Phelps
Sent: Tuesday, March 15, 2016 8:33 PM
To: Joe; amsat-bb at amsat.org
Subject: Re: [amsat-bb] Homebrew Up-Dated Eggbeater Antenna (correction)

This may not be a lot of help but you want RG-62.  You can buy it by the
foot but I do not have any,  I used mine up working on the WRAPS rotor.
RG-62 uses an RG-59 connector.
DougK9DLP

      From: Joe <nss at mwt.net>
 To: amsat-bb at amsat.org
 Sent: Tuesday, March 15, 2016 3:45 PM
 Subject: Re: [amsat-bb] Homebrew Up-Dated Eggbeater Antenna (correction)

Main problem seems to be the 93 ohm coax,,,

anyone got a short piece?

Joe WB9SBD
Sig
The Original Rolling Ball Clock
Idle Tyme
Idle-Tyme.com
http://www.idle-tyme.com
On 3/15/2016 3:11 PM, Robert Bruninga wrote:
> 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
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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.
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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!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb