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Help With A Yagi


airman_dopey
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Hey guys,

Been a fan of the show for a while and finally decided to start learning by doing.

I picked up the ALFA 036H with the 7DBi panel antenna and started having a blast. With neighbor's permission I started branching out only to find that the panel antenna was just not good enough to get further than my immediate neighbor's house (and barely that far at that). So I saw the Yagi antenna on the show and decided to buy one.

I ended up waiting 2 weeks to get this: http://dx.com/p/2-4ghz-100w-18dbi-directional-high-gain-18-unit-antenna-for-wifi-wireless-network-sma-34759?item=3 and mount it to the Vanguard tripod mentioned elsewhere in the forums.

I figured it would work well with the shorter cable and higher gain. Low and behold, it shows up and I get a WORSE signal than with the Alfa Panel antenna.

My question is this: am I doing something fundamentally wrong here or did I just buy a crap antenna? If the later, do you have any suggestions for a GOOD Yagi antenna, or will the hakshop be getting any more of the antennas in? I'm not concerned with spending the money if I get quality, but I had heard nothing but good things from dealextreme (minus the shipping time).

Thank you for anyone willing to help me out. In the meantime I'm going to keep searching. =)

-James

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  • 3 months later...

For anyone else looking for a different Yagi, I ended up purchasing the black cantenna (first link) and am thoroughly impressed with it. Also threaded for camera tripods so the vanguard tripod worked well with it.

I personally prefer dish to yagi because yagi have very narrow beam which make it difficult to aim and they are very sensitive to polarisation so if the router you are trying to reach doesn’t have its antenna straight, you will get better result with it tilted (which most mast mount doesn’t do) yagi are good for point to point with 2 of them equally polarised. Dish on the other hand have few more degree of aim and, while still being polarised, doesn’t care that mutch unless you are going extremely far and will get you a decent signal (I think the world record was something like 400km LOS with dish!). I had mixed experience with small dish/panel but they do improve the gain significantly but come with cable too long most of the time. My best experience was with a 2ft large grid dish was getting 36db of gain, I couldn’t find a place in LOS far enough to lose the signal, I was using it to reach my office a few km away with a row of tree in the way and bellow the proper Fresnel zone.

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I am assuming by "dish" you mean a parabolic (especially given the gain you mentioned). Could you please link a parabolic that has a larger cone than a yagi? Yagis typically have over double the beam width a parabolic has, making them far easier to aim, not harder.

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Parabolic dish

grid_vert.jpg

Yagi

yagi_vert.jpg

You are right, Yagi should be easier to aim, however, RF efficiency is really case by case, there are so many factor that will make one or the other better. In my own test, with a yagi and parabolic with same gain side by side, I couldn’t see the yagi 2km away but was getting good signal with the dish. In my specific case, I had to shoot it between tree that was half way (1km) that's maybe why the dish had better success for me. thanks for pointing out that I was wrong with the cone, I know what I know by trying stuff, never really did the math.

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No worries. Typically a parabolic will have a 7-9 degree cone. Most yagi will range anywhere from 18-31(ish) depending on gain. However, parabolic will ALWAYS have a higher gain and will reach MUCH further distances. With that said, you are totally correct that it depends on personal needs. My requirements dictate that a parabolic will not work for what I am trying to do. In your case, a yagi would not meet your needs.

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we use the dish style setup and base station sectors for our long range stuff, A LOT of nano locos. usually only use ubnt products.... www.ubnt.com , but we have ran a few yagi's as well.. That being said, after testing the limits of reach on all of their products... we showed far better results from a custom PRINGLES CAN!! lol. piece of all tread with washers spaced evenly, etc. google can show u how to build... what freq. are you running? i would assume 2.4 & 5 ghz? That ant. is 2.4 ...Yagi has to been pretty much line of sight to do any good, but can reach... if you have a yagi on a tripod, you need to have the ap visible. that antenna looks bad though...any obstructions as you prob. know will slow 2.4 & 5ghz down. the wave length is short, even shorter on 5ghz.. so overall what i am trying to say is if you are just hunting wifi, war driving or whatever... the alfa kicks butt. if you really want some "long range wifi" you need to look @ the 900mhz stuff... but not many ap's will use that..... we have made yagi's reach over 2 miles@2.4ghz... that is 80ft up and line of site... i guess i should ask what it is you are doing? alot depends on the power at the other end... you may have the power to reach it... but it may not have the power to get back to you.

Edited by jesseconsopolus
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