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Ars Technica has an article about Linksys committing to maintaining open source firmware usage for the WRT series of routers. This is a follow up to a previous story that ran when the original announcement regarding FCC (Federal Communications Commission) enforcement of 5.8 Ghz part 15 device requirements came out. At least there remains one well known product that decided to implement the requirement in a way that is consumer modification friendly. From the article:
Any 5GHz routers sold on or after June 2 must include security measures that prevent these types of changes. But router makers can still allow loading of open source firmware as long as they also deploy controls that prevent devices from operating outside their allowed frequencies, types of modulation, power levels, and so on.
This takes more work than simply locking out third-party firmware entirely, but Linksys, a division of Belkin, made the extra effort. On and after June 2, newly sold Linksys WRT routers will store RF parameter data in a separate memory location in order to secure it from the firmware, the company says. That will allow users to keep loading open source firmware the same way they do now.
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Though I disagree with this notion
Although Linksys has proven that open source firmware can still be used under the new FCC rules, it's clear that options for open source users will be more limited than they are today. Kaloz wishes the FCC had taken a different approach, one focused on punishing people who cause interference without preventing legitimate uses of network hardware.
Is the suggestion that the Doppler weather radar in use at airports is less important than getting cat pictures from the comfort of your couch and not having to run an extra Ethernet cable? Because Delta Flight 191 is why these airport Doppler weather radar systems exist at all. Do we punish before or after the crash? As well I don't think there is an appreciation for just how hard it is to find malfunctioning transmitters: it can be done but with significant amounts of work. The FCC is not funded for this level of enforcement right now. Everyone must share the very finite electromagnetic spectrum. I don't have a problem giving life and safety critical systems priority over cat videos.
As a quick experiment locate your WiFi router and check the verbiage. I'm sure everyone has seen the part 15 text but probably never paid attention to it. You will find This device may not cause harmful interference as well as this device must accept any interference received. That's because the weather radar, by design, gets to break you but you don't get to break it.
(Score: 2) by JNCF on Sunday May 15 2016, @06:24PM
The whole point is to isolate the internal electromagnetic field from external fields. Since the internal field of a conductor is zero, the exterior for a conductive sphere will take the point charge. That is, nothing will get through.
This is hyperbole, as I'm sure you're aware. Compasses work inside of faraday cages. A strong enough field will get through.
As for the grounding, it's purely a safety and regulatory issue. The charges will still arrange on the external surface so the internal field will still be isolated.
But the charge will stay on the outside surface of the ungrounded cage. If it were grounded, the charge would quickly disperse into the ground. My understanding - rightly or wrongly - is that the electromagnetism on the outside surface affects the electromagnetism on the inside surface, and viceversa. This basically doesn't happen with a grounded cage because the electrons don't stay long enough to matter. I'm totally open to being wrong, but I'm not convinced that I am from the video you linked. In the video, there is no significant charge on the inside surface of the ungrounded faraday cage. To show the interaction I'm talking about, you would need a significant source of electromagnetism inside of the cage as well. I'm not at all surprised that the foil on Benjamin Franklin wasn't visibly disturbed.
(Score: 2) by RamiK on Monday May 16 2016, @07:38AM
hyperbole, as I'm sure you're aware.
Without going into the static vs. dynamic models, I can generalize and say it's a force so a huge field like the earth's will need a huge power source to cancel out completely in low frequencies. Regardless, here's a static analysis: https://people.maths.ox.ac.uk/trefethen/chapman_hewett_trefethen.pdf [ox.ac.uk]
the charge would quickly disperse into the ground.
When saying grounding, we're talking about standard PEN earthing systems... Not a physical pole stuck in the ground. There's a regulatory 5-20Ohm between the ground electrode and the power source. But it's a complicated subject so instead, lets simplify our model and say we're not grounding the power source by using coils (like an arc welder). That will mean the circuit never closes through the ground if touching the cage. It's not actually how emp shielding is done in practice but it's the most I'm willing to cover in a single paragraph. You can look up the real circuitry here: https://en.wikipedia.org/wiki/Earthing_system [wikipedia.org] .
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