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Simple Wi-Fi Yagi (2014)

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Re: Simple Wi-Fi Yagi (2014)

#61

Post by aidenn0 »

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 only illegal if you get net gain out of it[1]; if you turn down the power so that the maximum power transmitted in any direction is the same as before, then it's legal. You can get a small performance improvement by using directional antennas in this way as you reduce the received strength of off-axis signals which can reduce both multipath interference as well as interference from other stations.

It's not all that useful indoors though as 2.4 and 5GHz signals bounce off of walls really well so you lose much the directionality at the very first wall it hits.

1: Actually there is a total ERP requirement, but most routers with external antennas are already close to that requirement, so more than about 3dB gain will often put you over.

Re: Simple Wi-Fi Yagi (2014)

#62

Post by aidenn0 »

ac29 wrote: post #58
swiley wrote: post #56

Earlier quoted context omitted.

You're not allowed to mix and match antennas on mass produced Part15 devices, regardless of the ERP. That never seems to stop anyone though.

Citation? Plenty of commercial part 15 devices don't even come with antennas, requiring you to "mix and match", unless I misunderstood what you meant by that.

http://www.ecfr.gov/cgi-bin/text-idx?SID=c2dc3c7e7691816d126...

Re: Simple Wi-Fi Yagi (2014)

#63

Post by dragontamer »

vinhboy wrote: post #26

So this makes the router sends a stronger signal, farther. But how does this help if my laptop still has the same wifi adapter and can't send a strong signal back?

Antennas are coupled. Transmitting is receiving, and receiving is transmitting.

When you pull on a chain or a rope, it doesn't matter if the other side is "receiving" the pull, or "sending" it. The two sides are physically coupled.

Similarly, antennas are physically coupled to each other. Increase the gain on one side, the other side still benefits. You're physically connecting a "rope" of electrons over the air.

Re: Simple Wi-Fi Yagi (2014)

#64

Post by dragontamer »

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.

> dipole antenna

Erm, looks like a monopole antenna to me. The rest of your post looks correct otherwise.

Re: Simple Wi-Fi Yagi (2014)

#65

Post by bsamuels »

baq wrote: post #38

if my router has 3 antennas, is there any point to installing it only on one of them? my intuition that's based on exactly no RF experience whatsoever tells me that it'll do more harm than good. (case is weak 5GHz signal in the corner of a house.)

theres a two reasons your router probably has 3 antennas:

-beamforming

-split 2.4ghz/5ghz/5ghz-wave2 antennas

if your router is using those three antennas for beamforming, you might trigger some strange behavior if you yagi a single one of them. if run into issues and can turn beamforming off, you should be able to yagi a single one no problem.

if your router pumps each antenna into a separate radio, then you can reliably pump a single radio into that corner of your house w/ a yagi. however, you won't have seamless roaming between the 2.4ghz and 5ghz networks when you move into and out of that corner of your home.

i recommend getting a mesh network, they're the bees knees and are a huge step above the traditional access point + range extenders model

Re: Simple Wi-Fi Yagi (2014)

#67

Post by kale »

anfractuosity wrote: post #66

Basic antenna question: I thought with Yagis the elements where connected together, is that not the case? As they seem to be held just by plastic.

No, Yagis have a single driven element like a dipole, and you have longer elements behind the driven element (reflectors), and shorter elements in front (directors I think?).

Re: Simple Wi-Fi Yagi (2014)

#68

Post by anfractuosity »

kale wrote: post #67
anfractuosity wrote: post #66

Basic antenna question: I thought with Yagis the elements where connected together, is that not the case? As they seem to be held just by plastic.

No, Yagis have a single driven element like a dipole, and you have longer elements behind the driven element (reflectors), and shorter elements in front (directors I think?).

Interesting, thanks!

Re: Simple Wi-Fi Yagi (2014)

#70

Post by tropo »

colanderman wrote: post #11
aray wrote: post #9

Earlier quoted context omitted.

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 A…

He's not operating under FCC part 15. He's using FCC part 97 instead, with the appropriate license.

His rules: 1500 watts PEP, unlimited EIRP, channels 1 to 6 only, no encryption

That's better than a normal microwave oven.

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