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Simple Wi-Fi Yagi (2014)

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Re: Simple Wi-Fi Yagi (2014)

#51

Post by colanderman »

throwaway7767 wrote: post #48
lucb1e wrote: post #42

Earlier quoted context omitted.

> the common case that the AP sits in a corner of a one-story house I was going to make it the centerpiece of the living room but my girlfriend vetoed that.

When you upgrade from consumer-grade equipment into dedicated APs, they start looking more like something you can put into the center of your living room without being ashamed of it. The Unifi APs for example look like oversized smoke detectors. They have obnoxious blue LEDs like seemingly all modern equipment, but you can turn them off and then it emits no light at all, and fits quite well into the living room when…

Mikrotik has been moving in this direction as well. This sucker [1], while unfortunately 2.4 GHz only, is an inconspicuous 3.5" white circle you can stick on your ceiling.

[1] https://routerboard.com/RBcAPL-2nD

Re: Simple Wi-Fi Yagi (2014)

#52

Post by colanderman »

diminoten wrote: post #32
colanderman wrote: post #19

Earlier quoted context omitted.

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 lin…

It is illegal, according to another comment: https://news.ycombinator.com/item?id=13459834

As I said in that comment, it's perfectly legal (and useful) so long as you turn down your TX power a bit.

Re: Simple Wi-Fi Yagi (2014)

#53

Post by colanderman »

Spare_account wrote: post #35
colanderman wrote: post #11

Earlier quoted context omitted.

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…

OK, so if by the time the signal exits my property it has dropped below mandated limits, there is no harm done right? If I aim my antenna such that I contain the illegal power region within my property, will there be an unintended consequence? To be clear, I'm referring to a house not an apartment so I don't have any concerns about upstairs or downstairs neighbours.

RF energy doesn't quite work like this. If your transmitter has a high EIRP (either due to antenna directionality or high TX power), then its signal is going to travel a long way, even after the signal level has dropped to that of a lower-EIRP transmitter. That is simply the inverse square law at work.

You could place sufficiently absorptive materials that this isn't so (e.g. enclose your house in a Faraday cage). But as hydrogen18 points out you're still limited by the FCC.

Re: Simple Wi-Fi Yagi (2014)

#54

Post by colanderman »

hydrogen18 wrote: post #50
Spare_account wrote: post #35

Earlier quoted context omitted.

OK, so if by the time the signal exits my property it has dropped below mandated limits, there is no harm done right? If I aim my antenna such that I contain the illegal power region within my property, will there be an unintended consequence? To be clear, I'm referring to a house not an apartment so I don't have any concerns about upstairs or downstairs neighbours.

No, that is incorrect. The domain of the FCC extends to all property of the United States of America, be it public or private.

The reason this is important is that it prevents private corporations from interfering with public air space (as discussed previously on HN [1]), and prevents landlords from interfering with the rights of tenants to legally place outdoor antennas (such as satellite dishes).

[1] https://news.ycombinator.com/item?id=8406022

Re: Simple Wi-Fi Yagi (2014)

#55

Post by Cerium »

MayeulC wrote: post #29

As an electronics student, are there any resources I could use to learn the basics of RF (antennas, etc)?

Take a microwave design class. This would be a second or third course after electrostatic, electrodynamics, then something like microwave theory. At my school we had to petition for the course as a special section. It was great, we built cavity resonators, and final project was an antenna design. All the way from theory, then using modern fea antenna software, and then building it and testing performance. If you have any interest take it. I was not going to but the professor said: "Phil, what's the lower end of the microwave spectrum?", I said "1 GHz", he then asked "How fast is your computer?", I replied "2.8 GHz", He said "I'll see you next semester then?". these days having an understanding of microwave theory will help you no matter your specialization.

Re: Simple Wi-Fi Yagi (2014)

#56

Post by swiley »

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.

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.

Re: Simple Wi-Fi Yagi (2014)

#57

Post by tlrobinson »

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...

Note that licensed ham radio operators are allowed to operate at (much) higher power on the WiFi channels that happen to overlap the 13cm ham band.

http://w5vwp.com/wifihams.shtml

(Of course then you are subject to all the Part 97 restrictions like no encryption, no commercial use, etc)

Re: Simple Wi-Fi Yagi (2014)

#58

Post by ac29 »

swiley wrote: post #56
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.

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.

Re: Simple Wi-Fi Yagi (2014)

#59

Post by Splendor »

jlgaddis wrote: post #39
MayeulC wrote: post #29

As an electronics student, are there any resources I could use to learn the basics of RF (antennas, etc)?

You might start at the ARRL's Antennas page [0] and consider the ARRL Antenna Book [1]. Most of that is aimed at amateur radio in particular but the theory is the same. There's tons of free and/or open-source software (of varying quality) for modeling antennas and such as well. [0]: http://www.arrl.org/antennas [1]: https://www.arrl.org/shop/ARRL-Antenna-Book-23rd-Softcover-E...

And/or find a local ham radio club.

http://www.arrl.org/find-a-club

Re: Simple Wi-Fi Yagi (2014)

#60

Post by aidenn0 »

swiley wrote: post #56
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.

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.

The FCC has stated that the RP-SMA connector (the connector used on nearly all wifi routers that have detachable antennas) shouldn't be allowed on part 15 devices, but also that it will delay enforcement of this indefinitely[1]. So even the FCC is fairly "meh" on enforcing this unless actual interference is reported.

1: http://hraunfoss.fcc.gov/edocs_public/attachmatch/DA-00-2225...

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