[aray]

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...

[colanderman]

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.

[Spare_account]

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.

[hydrogen18]

No, that is incorrect.

The domain of the FCC extends to all property of the United States of America, be it public or private.

[colanderman]

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

[colanderman]

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.

[ocdtrekkie]

I 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]

I think this falls under the pragmatic category of "you're only breaking the law if you get caught."

[ocdtrekkie]

Oh of course, and there's actually a surprising number of FCC rules you'll never get caught breaking. GMRS license violation is another.

[tropo]

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.

[tlrobinson]

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)