8 ms·
Simple Wi-Fi Yagi (2014)
- modeless 10y agoWhat is the legality of this? I have a vague suspicion that operating a device like this would violate some FCC regulations.
- turbohedgehog 10y agoFCC regulations (afaik) only apply to the power output of the device, modifying the antenna like this shouldn't change the power output.
- audeyisaacs 10y agoIf it's like here in Australia, they do consider EIRP. So a directional antenna would increase the EIRP, but with just 100mw tx at the output, I doubt EIRP would be over the limit (4W for 2.4Ghz ISM in Australia).
- grahamburger 10y agoFCC regulates EIRP, which is output+antenna gain. For this to be strictly legal you would need to adjust the power down until the EIRP is within the legal limit. Actually to be strictly legal I think it would need to be type excepted by the FCC. That being said if you're using this in your home/office on a legal channel it would be really difficult to even tell from outside you were using it and almost certainly not worth the FCCs time to even try to watch for it. It's not that much extra gain over the stock antenna.
- colanderman 10y agoTo be fair, the FCC regulates both EIRP (4 W / 36 dBm) and max transmit power (1 W / 30 dBm). E.g. you can't just have a 34 dBm transmitter hooked up to a 2 dBi dipole.
- Johnythree 10y agoFCC 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.
- aray 10y agoGood 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_radiated_power https://en.wikipedia.org/wiki/Equivalent_isotropically_radia...
- colanderman 10y agoYep. 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 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.
- Spare_account 10y agoOK, 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.
- ocdtrekkie 10y agoI think FCC laws technically apply within your property as well. Hypothetically, what happens if your non-compliant device blocks a visitor on your property from calling 911?
- sjwright 10y agoI think this falls under the pragmatic category of "you're only breaking the law if you get caught."
- diminoten 10y agoRight? Why wouldn't the router companies include this somehow in their designs if it actually improved performance? Because it's illegal, is why.
- Yaggo 10y agoIt'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.
- jrockway 10y agoDipoles are directional too. There are nulls directly aligned with the antenna (above and below the router in this case). No doubt this accounts for some of the "my WiFi doesn't work upstairs" stories.
- colanderman 10y agoNo, 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 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 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.
- diminoten 10y agoIt is illegal, according to another comment: https://news.ycombinator.com/item?id=13459834 https://news.ycombinator.com/item?id=13459834
- agumonkey 10y agoI remember reading that unless you amplify the radio above 5W or something, there's no way you're above the regulated limit.
- colanderman 10y ago4 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).
- swiley 10y agoYou're not allowed to mix and match antennas on mass produced Part15 devices, regardless of the ERP. That never seems to stop anyone though.
- ac29 10y agoCitation? 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.
- aidenn0 10y agohttp://www.ecfr.gov/cgi-bin/text-idx?SID=c2dc3c7e7691816d12644e9ae2ee7cfe&mc=true&node=se47.1.15_1203&rgn=div8 http://www.ecfr.gov/cgi-bin/text-idx?SID=c2dc3c7e7691816d126...
- aidenn0 10y agoThe 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-00-2225A1.pdf http://hraunfoss.fcc.gov/edocs_public/attachmatch/DA-00-2225...
- bbayer 10y agoI am wondering if antenna calculations are applicable for all types of routers. If not, how can I adapt it to my own setup?
- bsamuels 10y agoitll be applicable for any 2.4ghz, 50 ohm radio
- fake-name 10y agoNot 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.
- bsamuels 10y agothere 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.
- dragontamer 10y ago> dipole antenna Erm, looks like a monopole antenna to me. The rest of your post looks correct otherwise.
- tumblen 10y agoCould something like this have any impact on a bluetooth antenna?
- mojoB 10y agoCertainly, though the output power is quite a bit less (20dBm for WiFi vs 4 dBm for typical bluetooth). http://www.tomsguide.com/us/how-to-bluesniper-pt1,review-408-4.html http://www.tomsguide.com/us/how-to-bluesniper-pt1,review-408...
- mediocrejoker 10y agoThis 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.
- colanderman 10y agoGiven that it's only somewhat directional, this would actually be useful for the common case that the AP sits in a corner of a one-story house. No sense sending all that RF energy outside, so direct it inside.
- lucb1e 10y ago> 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.
- throwaway7767 10y agoWhen 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 mounted on the ceiling.
- colanderman 10y agoMikrotik 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 https://routerboard.com/RBcAPL-2nD
- fovc 10y agoMy current (rental) place has the router and AP in one corner of the apartment, so signal strength at the other end is terrible. Is there a better (cheap but effective) option than this?
- vinhboy 10y agoSo 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?
- microcolonel 10y agoReciprocity says that path loss is equivalent both ways.
- stephen_g 10y agoIt also makes the antenna more sensitive in the direction its pointing. The elements make the antenna more directional, sort of focusing the energy. This increases the transmit side by concentrating the energy into a smaller area, but the same effect also helps it collect more energy. The trade-off is worse performance perpendicular to the extra elements.
- anotheryou 10y agoI'd guess it goes both ways, just like a speaker cone and the cone of an ear.
- dragontamer 10y agoAntennas 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.
- MayeulC 10y agoAs an electronics student, are there any resources I could use to learn the basics of RF (antennas, etc)?
- kogepathic 10y ago1. Find a university course on RF, look up the course textbooks. In my university we had several courses on "analog electronics" which covered topics like free space path loss and RF concepts (e.g. bandpass filters). 2. Use Google or another search engine (DDG) to find the book in PDF or EPUB version. 3. Enjoy reading the book without forking over hundreds of dollars to a greedy publisher.
- crwu 10y agobalanis
- jlgaddis 10y agoYou 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 http://www.arrl.org/antennas [1]: https://www.arrl.org/shop/ARRL-Antenna-Book-23rd-Softcover-Edition/?page=1 https://www.arrl.org/shop/ARRL-Antenna-Book-23rd-Softcover-E...
- Splendor 10y agoAnd/or find a local ham radio club. http://www.arrl.org/find-a-club http://www.arrl.org/find-a-club
- Cerium 10y agoTake 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.
- HNSucksAss 10y agoWhen he says the antenna in the picture is aimed to the right, does he might OUR right, or the router's right?
- baq 10y agoif 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.)
- geforce 10y agoDepends. Some routers have multiple antennas because there are multiple transceivers inside it, and some technologies (i.e. MU-MIMO in 802.11AC) will most likely react strangely having one of their antenna modified. In the end, it would probably make your performance even worse.
- bsamuels 10y agotheres 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
- amgin3 10y agoI wonder what this will do for my 20DBi external wifi adapter.. I can already connect to networks over 600 meters away from my 13th floor apartment..
- deleted 10y ago[deleted]
- anfractuosity 10y agoBasic 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.
- kale 10y agoNo, 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?).
- anfractuosity 10y agoInteresting, thanks!
- ramgorur 10y agointerestingly, the antenna optimizer (AO) software uses genetic algorithm to find the right the antenna topology, therefore, this antenna is not designed, it's evolved. more details can be found here: https://en.wikipedia.org/wiki/Evolved_antenna https://en.wikipedia.org/wiki/Evolved_antenna