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1-7 of 7 messages
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Eggbeater or turnstyle antenna?
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by W4TME on August 6, 2004
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I am planning to upgrade my UHF/VHF antenna system to something that will be more conducive to LEO satellite and ISS communications than the ˝ wave vertical that I am currently using. Unfortunately, I am not able to setup an AZ-EL system with yagis due to lots of trees and CC&Rs that will prevent me from mounting anything much above roof level without drawing the attention of the “home owner police”.
What I am considering is either making and “eggbeater” style antenna or a turnstile (two dipoles mounted at right angles and fed 90 degrees out of phase) for both 2 and 0.70 meter operation. Both antennas will produce an omni directional pattern with horizontal polarization. I suspect that the eggbeater will be a little quieter since it is a loop rather than a dipole. I do plan to put mast mounted LNAs on both antennas.
Does anyone have experience with these two antennas and can provide some wisdom and guidance on what might work best for my situation.
-Tim W4TME
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RE: Eggbeater or turnstyle antenna?
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by WB5HZE on August 6, 2004
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This link may be of help . . . while I've not built/ used these antennas myself they seem to have a good rep locally . . .
http://members.aol.com/k5oe/
Ron WB5HZE
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RE: Eggbeater or turnstyle antenna?
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by KQ6EA on August 6, 2004
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I've built several of K5OE's Eggbeater-II antennas, and they work quite well. Just follow his instructions for tuning the loops, and you'll be fine. One nice thing about Jerry's version, is that it has more gain towards the horizon, where you need it, compared to a turnstyle or M2 Eggbeater.
Jim KQ6EA
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RE: Eggbeater or turnstyle antenna?
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by N6AJR on August 6, 2004
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I tried to build a couple and they were less than good for me.. I now have a az el setup mounted at about 10 feet and it does well except for the low horizon stuff
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RE: Eggbeater or turnstyle antenna?
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by K0RFD on August 7, 2004
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K5OE's site as already recommended is a good one.
Jerry's a good man. Worked him many times. His antenna designs are very practical.
If you're working LEOs, you can build an azimuth-only system that will work better than any of the omni antennas. A yagi isn't that much harder to build than an eggbeater. A quad can be fed on adjacent sides through a phasing harness and actually give you circular polarization.
How can you get away with azimuth-only? Easy. Most people think that a satellite antenna needs to look "up" -- this is horse hockey. Back when UO-14 and AO-27 were active, I sampled all the passes for two weeks every 30 seconds with a tracking program. Both of these birds are in so-called "sun synchronous" orbits, as is the new Echo. I found that the average elevation for these satellites during a pass at my QTH was 14 degrees above the horizon. The APPARENT motion of the bird is MUCH faster near the zenith (when it is moving PAST you at 17,500 mph), so the satellite spends a much higher percentage of the pass close to the horizon (were it is moving TOWARD you or AWAY from you at 17,500 mph). And with a sun-synchronous orbit, passes that go RIGHT overhead are fairly rare, maybe two a week. You can use this to your advantage.
You need most of your gain near the horizon. That's where you have the most path loss. And the satellite spends most of its time near the horizon. So if you build an antenna with moderate gain, say a 4- or 5-element yagi or a 3- or 4-element quad, permanently point it maybe 10-15 degrees above the horizon. (And please DO use a mast-mount receive preamp!) The pattern will be wide enough to still "see" the zenith, albeit with much less gain, but you don't need the gain up there. You'll get most of your gain where the satellite is hardest to hear. An antenna with a 45-60 degree -3dB beamwidth works well for azimuth-only use. At 2 meters and 440, the boom lengths are plenty short enough to turn with an inexpensive TV rotor.
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RE: Eggbeater or turnstyle antenna?
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by K2WH on August 7, 2004
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K0RFD:
"Horse Hockey"? I guess I'm one of those that thought you wanted a satellite antenna to look "Up". Stupid me. However, I believe you are correct in your analysis of the amount of time the satellite spends below the zenith or its highest point in relation to your location. This would be correct if you could "See" the horizon from your location. My particular location however, does not allow me to see the satellite in any direction unless it is at least 20 degrees high. I live in a valley that from space might look like a crater.
So, looking up with my eggbeaters is a plus. Putting more signal at my horizon would be a waste of RF. Getting back to the original question, I have used both commercial antennas for 2 meters and 440mhz. I believe they are manufactured by "M2"? They worked great with DFQ signals into the satellite. My eggbeaters had the radial kit below them for enhanced signal strength about 30 degrees.
K2WH
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RE: Eggbeater or turnstyle antenna?
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by K0RFD on August 8, 2004
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K2WH:
Remember, it's not JUST the amount of time the satellite spends at low elevations, it's the amount of path loss also. You need more gain where the path loss is the greatest; you need less gain where there is less path loss.
Mapping your "personal" horizon is a good thing to do.
It's important not only from the standpoint of your antennas, but also timing the AOS and LOS of each pass.
I took out my trusty Brunton compass one day, went up on the roof where the antennas were, and mapped the apparent horizon at this QTH. Even though we're in a valley with about 2000-3000 feet of relief to the north and south and 6000 feet of relief to the east, there was nowhere at this QTH that the apparent horizon was higher than 8 degrees in any direction. The average in most directions was about 4 degrees. Our valley must be a whole lot wider than yours--20 degrees is pretty substantial.
IF you had good luck with eggbeaters, great. I didn't. Like many commercial designs, they are a compromise designed to work acceptably well in a wide variety of situations. Nothing wrong with that. On the other end of the scale, if I had the money for a couple of long-boom yagis and a computer-controlled alt-az system, I wouldn't be involved in this conversation. Have the computer point the beams at the bird and talk. Nothing wrong with that either!
But there is a middle ground too. By building instead of buying, I was able to design for my own QTH and budget. I did my homework, did some geometry, modeled lots of designs according to the gain, beamwidth, and front-to-side ratio I wanted to achieve. What I ended up with was a system that put gain where the satellites were most of the time, and where the gain was most needed to overcome path loss. I discovered that by going outside the "conventional wisdom" and abandoning the "straight up" paradigm, I was able to achieve more usable minutes per pass for the money I had to spend.
As they say in the commercials, your mileage may vary.
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