Obviously it would be illegal, and I promise I'm not gonna do it whatever your answer is :p
depends, hence the checking.
> And is that sort of violation the kind of thing your local regulator would be scanning for and send someone out to shut you down?
highly doubtfull
It'll still be possible to locate it with that info but it's more work unless you manage to interfere with two radars and they can triangulate. That's pretty unlikely for an indoor access point with only a few milliwatts though.
I was mainly referring to the 'radars are good at pinpointing things' comment from the OP :) I wanted to clarify that an AP on this frequency won't show up as a dot on a radar screen. For the distance to be captured it must have an actual reflection.
You can even see some of the lines I mentioned in that pic!
There is even a software-based wifi demodulator (https://www.nuand.com/bladerf-wiphy/) so you can try to decode it from the IQ data, but they usually don't have enough bandwidth.
I may overestimate the angular precision of that though.
But you need to specially do this scan and carefully evaluate the maximum (tricky if it's transmitting only once in a while). When you are scanning normally, you are pointing a bit above the ground (you are scanning the sky, of course) and the beam may have several degrees at the ground level.
And regarding the reasons for DFS - it is not due to the radars posing interference for access points, it is the other way round. They are supposed to be able to pick up reflections from clouds and airplanes that literally carry less than a millionth of the power that a typical AP would radiate.
Here is an example: https://www.fcc.gov/document/fcc-fines-hinson-dangerous-misu...
> the FCC does not exist outside the US so is this relevant elsewhere?
Your own country likely has an analogue. Get thee to Google. Ofcom is the UK equivalent, for instance.
It just tells you who needs shot first.
What do I care about some law student latin?
I know the analog of the FCC in my country. I have not ever heard about them knocking on anyone's door, ever so that's why I'm asking questions?
The world is a bitch in that it is your oyster, right up until you start impacting something everyone else is counting on. In that case, it is not infrequent for one to be made an example of.
That law student Latin there is a reminder that in spite of you "not knowing" something, the world still turns, you are expected to do some level of research, and there are people whose job is to just search for violations, and dispense a Notice of Apparent Liability to the perpetrator.
Hell, Amateur radio operators run what they call foxhunts when they notice something odd going on, because spectrum misuse impacts everyone.
Messing with Doppler weather radar is a usually a big thing that impacts various important services. Even in relatively backwater countries you will get someone knocking at your door if you do this.
Here’s an example of what it can look like on the weather radar side: https://www.reddit.com/r/techsupportgore/comments/lnxdji/whe...
People who operate radars (in particular radars for weather forecasts) are now really upset of the recurring interferences that come from wifi devices with (illegally) disabled DFS. Keep in mind that weather forecasts is not only about consumer people watching TV to know whether tomorrow will be sunny or rainy, but is also safety-related (e.g. for flights and navigation. You don't want your flight to be caught in a storm !).
That kind of attitude (e.g. with openwrt) will at the end lead Radio administrations to require locked hardware (locked bootloader and signed firmwares) in order to ensure that DFS cannot be disabled (as required by administrations, at least in Europe). That would be a pity for any embedded linux geek...
Keep in mind that whenever a new application appears, detailed technical analysis and simulations have to be done with regards to the other applications in co-channel and adjacent channel/bands, both with regards to direct interference, aggregated interference taking into account the projected density of the new spectrum use, clutter/terrain, propagation models, geometries of antennas, filter characteristics, etc. And even then, administrations do their best to find the right balance and enable as many applications as possible (including unlicensed and SRD), but those are tradeoffs and sometimes administration take risks to foster innovation (and sometimes it proves it was too permissive for the new user, such as what is happening now with regards to wifi vs weather radars).
(N.B. I am not in the US, but I guess FCC works similarly to EU administrations - which I know very well).
Following the rules (DFS) is fair ask to be able to access these additional 5 GHz channels.
If you do cause interference with weather radar, there's actually a chance that the authorities take action. WiFi interference isn't hard to scan for at all, even or you disable broadcasting your SSID on the channels you're interfering on.
What does this mean? The DFS check doesn’t exist? Or they just reboot nearby devices several minutes apart to allow enough time for DFS to complete?
A lot of consumer routers I've seen don't even expose the DFS channels as an option to avoid this problem (looking at you Motorola mesh products). It's not a problem just kind of funny to see.
Firstly, a coverage aspect of the design which will ensure that any given spot has a primary and secondary (and sometimes tertiary) AP radio providing appropriate RSSI.
Secondly, a channel plan that ensures that the DFS channels are not allocated to the primary and secondary radios. So if a client station's primary AP get taken offline for a minute by DFS then that station can immediately roam to the stable channel and maintain a decent RSSI.
Additionally, there may be some environments where the DFS channels are not enabled on the equipment at all. For example, many cheaper devices (think low end android phones) don't support DFS channels at all, so if there are many such devices in the area (e.g. College campus populated by poor students) then every radio running a DFS channel is effectively a coverage hole and therefore better to not use those channels at all.
obtaining the govt certifications for using DFS channels does add to the cost of the chipset so cheapest chipset simply don't do it.
What's the best practise in other words
Then install OpenWrt (even on that TP-Link Archer C7 if you want), set "channels" to the list of channels that you identified (unfortunately this property is available only from the command line), and "channel" to auto. Then OpenWrt will select one of these channels after a one-minute delay, and jump away (but only to another known-good channel) if there is a radar.
We all pretend that WiFi is this magic thing that allows our devices to transmit data, but in fact there are all these little details of reality "leaking through" that abstraction.
For example, it seems that instead of power cycling everything at once, WiFi should be turned on first to ensure that there is sufficient time for 5 GHz to be available. I sometime reboot my TV, Router, WiFi, and set-top-box simultaneously by simply turning the power board they're all connected to off and on. From now on I'll do them separately and in sequence...
In my setup there is a fiber modem (outside the house), a Wi-Fi router, and then all the connected devices.
Oddly, the one that I need to restart the most, seems to be my Mac. Realizing, of course, the problem could still be on the router side, but turning wifi on and off on the laptop usually solves my problem.
I rebooted one device at a time for about a year and made notes about each failure. I didn’t see the pattern until I had done this for a long time.
Never really had a more fickle laptop as far as wireless goes. Only a VAIO VPCZ1 after ten years of abuse as a gaming machine/daily driver started to get close. Again though, that's after 10 years. A Macbook will manifest that behavior within the first year for me.
The frustration has gotten me to the point I'm reading up on USB/PCI-E/datasheets implementation/protocol details so I can actually try figuring out WTF could be the cause.
Also FYI you can rest assured that if you've engaged a semicompetent Wi-Fi professional to design the coverage in your office/campus/warehouse/etc then you don't need to worry about "the DFS problem" as it is well known and will have been accounted for in the design.