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Simple Wi-Fi Yagi (2014)

ham-radio.com

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Re: Simple Wi-Fi Yagi (2014)

#11

Post by colanderman »

aray wrote: post #9
modeless wrote: post #2

What is the legality of this? I have a vague suspicion that operating a device like this would violate some FCC regulations.

Good intuitions. FCC regulations restrict EIRP[0], which is essentially "what is the signal strength in the strongest direction". It's possible that increasing directionality of your antenna puts you over the EIRP limit (given how routers already try to get _really_ close to it to improve performance). [0] https://en.wikipedia.org/wiki/Equivalent_isotropically_radia...

Yep. Specifically you'd need to adjust your TX power down to 27 dBm (from a max of 30 dBm) for an AP, or 29 dBm for a station. http://www.air802.com/fcc-rules-and-regulations.html gives a nice summary.

Basically APs on 2.4 GHz are only allowed 36 dBm (4 W) EIRP, no matter what antenna shape. This is usually not a problem though, since stations tend to have weaker transmitters anyway, but will still benefit from the AP's enhanced antenna gain.

Re: Simple Wi-Fi Yagi (2014)

#12

Post by diminoten »

modeless wrote: post #2

What is the legality of this? I have a vague suspicion that operating a device like this would violate some FCC regulations.

Right? Why wouldn't the router companies include this somehow in their designs if it actually improved performance?

Because it's illegal, is why.

Re: Simple Wi-Fi Yagi (2014)

#13

Post by bsamuels »

fake-name wrote: post #6
bsamuels wrote: post #5

Earlier quoted context omitted.

itll be applicable for any 2.4ghz, 50 ohm radio

Not really. It's only really applicable to any router that uses a dipole antenna. Pragmatically, this means it's only really an option on routers with external whip antennas. Lots of routers have internal antennas, at which point you're going to have problems attaching the thing. Also, if the internal antennas aren't dipoles, it's not an option at all without significant redesign.

there are a ton of routers with replaceable antennas where the connector is coaxed directly into the front end, like in the article.

i assumed that anyone trying this would have one of those.

Re: Simple Wi-Fi Yagi (2014)

#14

Post by agumonkey »

modeless wrote: post #2

What is the legality of this? I have a vague suspicion that operating a device like this would violate some FCC regulations.

I remember reading that unless you amplify the radio above 5W or something, there's no way you're above the regulated limit.

Re: Simple Wi-Fi Yagi (2014)

#15

Post by Yaggo »

diminoten wrote: post #12
modeless wrote: post #2

What is the legality of this? I have a vague suspicion that operating a device like this would violate some FCC regulations.

Right? Why wouldn't the router companies include this somehow in their designs if it actually improved performance? Because it's illegal, is why.

It's not illegal per se, if you adjust transmission power accordingly. Router manufacturers generally don't use yagi because it's directional, requiring aiming, unlike omnidirectional dipole antenna. Modern wifi stations have much more sophisticated ways to increase range than passive antenna designs.

Re: Simple Wi-Fi Yagi (2014)

#16

Post by mediocrejoker »

This makes the antenna more directional. It increases the range in one direction while decreasing it in every other direction, so I'm not sure how well this would work for most people without relocating the router/AP.

That being said, it's a clever bit of engineering.

Re: Simple Wi-Fi Yagi (2014)

#17

Post by Johnythree »

turbohedgehog wrote: post #4
modeless wrote: post #2

What is the legality of this? I have a vague suspicion that operating a device like this would violate some FCC regulations.

FCC regulations (afaik) only apply to the power output of the device, modifying the antenna like this shouldn't change the power output.

FCC regulations apply to the device with the supplied antenna in place.

The antenna is not supposed to be replaceable, hence the reverse SMA connector on most modems.

Modifying the antenna in any way invalidates the type approval.

Re: Simple Wi-Fi Yagi (2014)

#19

Post by colanderman »

diminoten wrote: post #12
modeless wrote: post #2

What is the legality of this? I have a vague suspicion that operating a device like this would violate some FCC regulations.

Right? Why wouldn't the router companies include this somehow in their designs if it actually improved performance? Because it's illegal, is why.

No, because no-one wants a home AP that only works if it's pointed at you.

You can buy directional APs if you want, but they're usually used for outdoor point-to-point links, or as sector antennas. e.g. I just installed one of these today: https://routerboard.com/RBSXTG-2HnD in a place that needed a signal far from where the AP was. Usually patch antennas (like this product) are preferred over Yagis for microwave links due to their smaller footprint, and capability of dual polarization in a single package.

Better is if your indoor AP can transceive in more of a "pancake" shape, like this: https://routerboard.com/RBOmniTikU-5HnD Note that's almost the same gain as this home-grown Yagi (7.5 dBi vs. 8.5 dBi) but with a more useful directionality.

Re: Simple Wi-Fi Yagi (2014)

#20

Post by colanderman »

agumonkey wrote: post #14
modeless wrote: post #2

What is the legality of this? I have a vague suspicion that operating a device like this would violate some FCC regulations.

I remember reading that unless you amplify the radio above 5W or something, there's no way you're above the regulated limit.

4 W (36 dBm), and the 8.5 dBi gain of this homemade Yagi puts you over that if you're operating at 1 W (30 dBm) max transmit power (as some home routers do).
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