Yagi Best Antenna??

I am interested in purchasing 2 antennas for a wireless network that I am setting up between two houses. These are two houses that are out in the country, about 200 yards away from each other, but there are woods in-between the two houses. I am not sure what type of antenna that would be best to get. I thought about getting two 16 Element Weatherproof Yagi antenna's.

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I am not sure if this is the best choice I could make. Could you please give me any reccomendations that you have regarding what type of antenna I should use.

Thanks for the help.

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Ah, a perfect bird roost. The local avian population will love it. I hope you enjoy cleaning the bird droppings off the antenna.

Hmmm... $90 for 15dBi or $6/dB of gain.

Now, if you bought a 19dBi dish antenna, it would cost $41 or $2/dB of gain. See:

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like dish and panel antennas.

At 200 yards, almost anything over about 8dBi gain will function except for the trees. The trees are going to be a big problem depending on how dense they are. You can sometime shoot *UNDER* the tree canopy at trunk level as there's more space between the trunks and between the branches. I did that once in an orange grove, which worked just fine except when someone parks a truck in the beam path. It's difficult to predict the effects of trees and leaves as it depends on the thickness of the shrubbery. Can you see through the leafs? How many yards of foliage is in the way? What type of leafs (needle, thin leaf, thick leaf, wall of wood, etc)?

Where is your unspecified radio going to be located? Coax cable losses are substantial and will negate any antenna improvements if done wrong. You might consider mounting your unspecified wireless radios near the antennas. Also, be sure to waterproof any exposed coax connectors.

In general, OFDM does MUCH better than CCK for getting through foliage via multiple paths. Therefore, I would disable 802.11b speeds in your unspecified routers. I've found it more reliable to run at a fixed speed, usually 6, 9, or 12Mbit/sec OFDM. If the signal varies radically as the wind blows the trees around, you might try a fixed speed.

Reply to
Jeff Liebermann

50% wrong. The higher the gain, the narrower the beamwidth for a given class of antenna. Different types of antennas have different beamwidths for identical gain antenna.

-3dB beamwidth for different gain yagi antennas: gain -3db beamwidth dBi degrees 8 60 10 40 14 30 16 25

-3dB beamwidth for different types of antennas of roughly the same gain: Type gain -3dB Beamwidth dBI degress patch 13 38 yagi 14 30 planar 13 25 dish 15 19

Note that at 200 yards, even the narrowest antenna (dish) will still have a wide enough beamwidth to avoid alignment problems.

The front to back ratio (f/b) and sidelobes are a function of the design of the antenna and has little to do with the gain. It is possible to trade f/b ratio for gain on most antennas and optimize for one or the other. However, higher gain antennas do not automatically imply a higher f/b ratio. Actually, it's quite the opposite as high gain yagi's tend to leak more than low gain yagi's.

Line of sight is ALWAYS a straight line. No curvature involved, especially at 200 yards. I think you're thinking about Fresnel Zone clearance, which requires more unobstructed clearance at midpoint than visual clearance. At 2.4Ghz and 200 yards, the midpoint Fresnel zone clearance for one zone is 7.8ft radius. However, that's academic as the trees will probably cause more problems than the lack of Fresnel zone clearance.

Reply to
Jeff Liebermann

Hi, Yagi (Yagi Uda) antenna is gain antenna. The more element, the more gain. Higher gain means narrower beam of angle and higher F/B ratio. You'll have to experiment setting up from both ends for best signal strength. Think LOS(ling of sight). Radio wave LOS is not as straight as visual LOS tho. Good luck, Tony

Reply to
Tony Hwang


But there is also the simple fact that a parabolic dish will have narrower beamwidth for the same gain, and will have significantly fewer sidelobes, as a Yagi Uda design.

Where did you do tropo? That's what I did when I was young. I did satellite when I was old. And microwave for all of it.

Nahhh. Do *not* take it to email. Keep it here, for everyone now and in the future.

Reply to
Floyd L. Davidson

What's different is that this is only true for a single class of antenna such as a yagi. For a given gain, different classes of antennas (panel, patch, planar, biquad, dish, coffee can, etc) have different beamwidths.

You also threw the front to back ratio into the puzzle, which has absolutely nothing to do with the number of elements or the gain.

I'm 57 and still somewhat young. I used to design, repair, sell, and install the stuff. Now days, I just fix computers, play consultant, and answer questions in newsgroups.

You call this plain language? "Think LOS(ling of sight). Radio wave LOS is not as straight as visual LOS tho." It's just plain wrong. Microwave line of sight is a straight line unless you want to play over the horizon, ducting, or knife edge diffraction. For the distances and frequencies involved in 802.11, it's a straight line. How will your plain language answer help the original poster with his antenna selection question?

No thanks. I answer questions in newsgroups and mailing lists for free. Everyone learns from answers via usenet. Only the people involved learn from an email exchange. The questions that come via email, I cosider to be billable consulting. I charge $75/hr and it typically takes about an hour per question.

Jeff, AE6KS (formerly WB6SSY) BSEE. Cal Poly, Pomona CA 1971.

Reply to
Jeff Liebermann

You might consider 2 homemade tin can waveguide antennas looking at each other. They are high gain, as good or better than a yagi, extremely cheap and simple make. Many designs are on the net. I have one on the end of 30 feet of RG-6 75 ohm CATV cable linking with a router with stock omni antenna 400 feet away through an apple tree and it gets 90% signal (-56dbi) at a solid 54mbs.

Two 3.25 by 5 inch (ribed) pet food cans soldered together to make a

10 inch tube (waveguide) closed at one end. Solder a 7/32 dia by 3/8 long brass tube at 90 deg to the side of the can up 2.5 inch from the closed end. Use a drill same as the I/D of the brass tube and drill through the can making a clean hole. Obtain a sufficient length of 75 ohm 18 ga (no its not 50 ohm) low loss foam core CATV cable and measure 1.25 inch from the end then cut through circumference to the inner conductor. Twist and remove the covering, braid and dialectric core leaving just 1.25 inch of exposed inner conductor. Insert this into the brass tube and push it down firmly so the tube slides under the braid and over the foil wrap until the foam dialectric is flush with the inside of the can thus forming a 1.25 inch long 1/4 wave stub antenna inside the can. It helps if the end of the brass tube is first filed a little to form a rounded edge. Bind the cable tightly to the brass tube with a few turns of .025 lock wire, fish line or whatever, and weatherproof it with some RTV silicon. The PC end requires a connector to match, usually reverse SMA on a pigtail. I made my connector from a brass nut tapped out to 1/4 by 32 with another 3/8 brass tube soldered to it and a centre pin from a sacrificed DB-9 connector. Its installed on the PC cable end same as antenna end and screws onto the reverse SMA socket on the Wireless card. No expensive "N" connectors or exotic coax. Ensure the two antenna polarizations (ie vertical or horizontal) are matched by rotating one can for best signal. You may also want to experiment with different stub antenna spacing from the closed end of the can however its not highly critical and 2.5 inch works well for me. This post was sent through it. Good luck.
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Hi, What is different? Higher gain = more element = narrower beam angle. Used work in microwave, troposcatter, sattelite comm systems when I was young. Talking from experience with plain language. Want to go in detail in antenna theory? Then please do via email direct. Tony, VE6CGX BSEE, class of '66

Reply to
Tony Hwang

Hi Jeff, I see you are a Radio Ham over there on the west side. I am too here in UK and though now not so active, I may have worked you on 20m with my 2 element quad at about 8 mtrs high! Callsign: G4UYI Yes I have tried different antennas myself over the years, but now just stick to a 2mtr vertical for local stuff. I also repair and charge for my computer services. How times have changed eh?


Reply to
Bob H

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