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Comment by Aloha | Hacker News Reader

I don't think this is working the way he thinks it does.

What he's likely do is shielding the wifi receiver from co-channel interference, which is likely reducing the noise floor at the AP - which is giving him effectively more range, because now the AP can hear stations that are further away with greater ease.

I don't think this is giving expanded tx coverage lobes as his diagram indicates, its likely a function of lowering the noise floor that gives the extra coverage.

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Yeah, some devices can be extremely noisy. If you have a Chromecast or Google Home, for instance, turn Guest Mode off -- it creates a hidden network on the same channel as your AP.

My chromecasts have been acting up really badly recently, I've just gone and disabled guest mode on them all based on this information.

I think sehugg was talking about self noise ie the noise created by the AP's internal electronics

It is unconnected, so it will not dissipate anything (shield). Depending on whether or not it is positioned on a wave node, it will either be a passive reflector or director.

It won't be a satellite dish as the comment thread on the page mentions, though, which is both a passive reflector and a focusing device, whose curvature requires at least some level of precision to be of any help.

For something much more helpful, see http://ham-radio.com/k6sti/wifiyagi.htm

It need not be grounded to be an semi-effective shield, we're talking about frequencies that drywall will attenuate here. Think about it this way, if it can reflect TX, it can also reflect other cochannel signals from that direction.

It may very well be working in more than one mode - but I strongly suspect its a far better shield, than it is a forward power reflector. It also may strongly effect the VSWR of the existing dipoles used here.

A signal from the "correct" direction will have ~half its energy reflected towards the antenna, resulting in gain. A signal from the "wrong" direction will have ~half its energy reflected away from the antenna, resulting in attenuation. It won't shield, though. That requires that you dissipate the signal somewhere.

But to be fair, it's a wild guess. It's a semi-flat piece of foil placed at an angle, at a random distance from 3 individual antennas. That's why I linked to the nice and simple, easy-to-calculate yagi-uda for if you want to hack with antenna gain.

You'd effectively creating a multipath generator with this setup, which means you have the primary signal, then a couple microseconds later, a reflection that is probably 20db under the main signal.

No disagreement that the yagi thing you pointed out would work better.

That said, this is a MIMO router, so that may change the modulus on the multipath problem.

A reflection with just 1 microsecond delay would require a 300 meter reflection path (e.g. 150 meter to/from the reflector). I think you might be thinking of multi-path propagation within the context of long-distance communication (e.g., a HAM QSO).

A regular home Wi-Fi network is already a complex multi-path system, as the primary propagation mode is reflections from walls and ceilings, leading to plenty of self-interference with many hot- and cold-spots from constructive and destructive inteference. We are at most introducing a few stronger reflections in an already extremely reflection-heavy environment. The big question is whether it does any good, either through attenuation or gain.

As for MIMO, I must admit to not knowing much about it—I know it utilizes spacial separation to increase bandwidth, but I do not know much of its actual implementation, and thereby weaknesses.

Yeah, something so imprecise isn't likely to work as he thinks. Proper shielding can do a lot more. If you made your house/apartment a Faraday cage and eliminated neighbors' AP's that would already solve most problems.

> If you made your house/apartment a Faraday cage

Might put a crimp on your cell phone reception ...

Is there a way to build your Faraday cage to block out wifi wavelengths but not cell phone ones? How far apart are they?

You could likely block anything over 2.3 GHz and get away with it: https://en.wikipedia.org/wiki/Cellular_frequencies_in_the_US

unless you have Sprint ;-)

This is usually done with a femtocell.

[0] https://www.att.com/att/microcell/

I've always wondered what it would be like to have paint like this as an exterior primer

https://www.lessemf.com/paint.html (Warning: this site gets a little silly)

I can see this working well, unless LoS goes through one of those walls. There's a metal mesh in most of the walls of my house (putting two routers directly opposite each other on either side of an internal wall will cut the signal strength to about 60%), and trying to get a reliable signal because of the shape of the house (roughly L-shaped) was a nightmare (line of sight was through two external walls).

Just move to the 5.8ghz band. There's an extra 50MHz of bandwidth available and these frequencies are much more strongly attenuated by walls. There's also usually much less interference from other unlicensed equipment like cordless phones, baby monitors and microwave ovens, although you can occasionally get hosed by a dodgy Chinese video sender operating at well above the legal limit.

You might need to replace a couple of older pieces of equipment, but it's a hell of a lot cheaper than turning your house into a Faraday cage.

Will changing the Channel help in this case?

doing a proper site survey and changing channel would help - you need to see what channels interfere in each quadrant of the building, and then choose accordingly. You're also generally better off on a channel with one moderately strong cochannel station, than 10 weak cochannel stations.

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