Review of Antec skeleton case neglects to mention RFI issues

I will admit to being fascinated by Antec’s latest case. It’s more of a skeleton than an enclosure, providing mounting points for all of a computer’s components to screw into, fans, and nothing else. I especially like how up to four additional hard drives (in addition to the two it fits “internally”) can be clipped onto the outside. Despite the case’s goofy novelty, this really is something I could get into. I tinker with my computers a lot, often running them with the sides off in between swapping out hardware, so this wouldn’t be that much of a stretch. Heck, I’ve run computers with IDE ribbon cables connected to “external” hard drives sitting on top of the case; the skeleton case’s mounting option would’ve been really nice. And above all, I just like the idea of being able to see the components in my computer (which I paid quite a bit of money for) at all times.

But I’m also a bit of a realist. There is a good reason that all other consumer-level computer cases are, well, cases: it makes sense to put your computer’s delicate vitals inside of an enclosure. The case helps keep dust out. It also keeps objects from falling onto the computer’s components. Drop a sizable object onto a normal computer case and the worse that will likely happen is a large dent in the case. But even dropping a coin into the internals of an exposed skeleton case could short out some contact points on the motherboard, or get caught in a fast-spinning fan and turn it into slying shrapnel. Dropping anything larger could easily cause substantial damage to delicate internal components that a 1mm thick steel case wouldn’t blink at. And let’s not forget the problem of spilling food or drink. Spill something on top of a normal case and odds are good you can quickly wipe it up before it seeps in (and the case itself will deflect most of it). Spill something into a skeleton case, and you’re almost guaranteed some kind of catastrophic failure.

But even if you’re never clumsy, and you set up your skeleton case in such a way that there is zero probability of anything ever falling on/into it, there is another less obvious problem lurking: radio frequency interference (RFI). One of the reasons computers and most other electronics are sold enclosed in metal cages is to prevent RFI (even when the exterior is plastic, there will be an internal metallic Farraday cage enclosing the electronic components). Electronics are sold this way because of a sensible regulatory requirement by the FCC to prohibit your household electronic devices from interfering with other devices. Since the skeleton case doesn’t ship with any electronics in it, it can get past the FCC, but no computer retailer would be able to sell a pre-built computer inside a skeleton case. Computers, having all sorts of components in them running at various clock speeds, produce quite a number of radio waves of various frequencies.

The RFI produced by a computer can potentially interfere with nearby electronic devices. It might cause a hum on a speaker system, for instance, or produce static on a radio (ham radio operators on HF frequencies especially should stay far clear of skeleton cases). Depending on how severe the RFI produced by the computer is, and on which wavelengths, it could interfere with wireless mouses and keyboards, or even a monitor. There’s no way to be sure, really — the specifics of RFI are really finicky, and depend as much on the characteristics of the receiving device as of the computer in the skeleton case. The interference also works both ways, so your computer could suffer some rather catastrophic crashes if parts of its circuitry happen to be resonant with a nearby source of radio waves. Considering that I pick up low power AM radio through my bass guitar’s unshielded instrument cable when I turn the gain all the way up, it’s not far-fetched to imagine interference affecting an unshielded computer as well.

But I’m just making educated guesses. What we really need is cold hard data on how much RFI an unshielded computer puts out, and what sources of radio waves one might expect to interfere with the computer. Unfortunately, ExtremeTech didn’t examine this angle at all in their review, and my lack of a test bed (let alone the willingness to pony up $190 for the case) precludes me from finding out myself. So I really wish someone would do the requisite experimentation, because the skeleton case concept could be completely DOA for reasons less obvious than “you might drop stuff into it”.

5 Responses to “Review of Antec skeleton case neglects to mention RFI issues”

  1. Ed Says:

    A friend’s computer always has all the panels removed, basically working like a frame that supports the rest. He noted that he hardly notices any interference nowadays, having had a number of different motherboards in it throughout the years. I’m guessing newer motherboards cannot afford to dissipate power in the form of radio energy. An extra guess is that interference created on one side of a board would cause parasitic signals to show up on another side, so it’s better do do your homework right and ensure all the lanes and connections have a properly adapted impedance.
    Another point to note is that almost all equipment is now digital. Before, we had analog radio and analog tv, now radio is mostly gone and tv comes through a properly shielded cable into our homes. All this new digital equipment is less prone to letting itself get interfered. Surely, I agree that getting rid of all these guesses is the way to go. RFI should be properly measured. In order to comply with the FCC rules, I’m sure most manufacturers do it when they release a new product. (ehehehe, I bet even Antec did some of this, but just kept quiet.)

  2. Kelly Martin Says:

    Ed:

    Properly-shielded cable TV cables? Bwa hah ha. There isn’t a cable company in the country that has its cabling properly-shielded end to end. Why do you think that most cable companies put an unimportant channel on Channel 18, or have that channel unassigned entirely? Why do you think that W9DUP had to move from 145.25 to 145.43? Cable companies leak massively, and rarely bother to repair the leaks because they have lobbyists who will just lean on the FCC should anyone complain. FCC regs on EMI are widely ignored, and the FCC doesn’t care unless it interferes with a licensed service (and even then only if the licensed service is operated by a company with lobbyists). See also this article from my blog, on the vagaries of FCC enforcement.

    Digital signalling is not less prone to interference, it’s just that the interference is less obvious. Instead of getting loud, distorted speech you just get dropouts. We see this all the time on our digital cable channels; black squares of doom when the mpeg stream loses too many segments, or no audio for a few seconds. Digital TV (and digital radio) actually require higher signal-to-noise ratios in order to get a usable picture because of the deep compression the broadcasters use to squeak every last dreg out of the bandwidth. This makes them more prone to interference, not less, because any interference cuts into the available SNR. Also, digital signals generally do not gracefully degrade the way analog does; with digital it’s generally all or nothing.

    About the only thing that avoids these are solutions that are optical fiber end-to-end, and last-mile fiber is, as of yet, not widely deployed.

  3. Cyde Weys Says:

    Yeah, I have to back up Kelly here. I pick up all sorts of interference from cable TV on my ham radio transceiver. I know it’s cable TV because cable TV audio is FM, meaning I can actually listen to it on transceiver. I’ve used frequency charts showing where the cable channels and local listings and, sure enough, I can reliably tune into just about every cable program being broadcast in the area at 6 MHz increments.

    Even worse, some of it interferes on the ham radio bands. Grrrr.

  4. Greg Maxwell Says:

    In a prior professional role I had the interesting job of acting as a government regulator over a local cable company. In short: Preventing leaks is hard. Fixing leaks is expensive. The cable company was not evil, but the strategy that would maximize their profit was to perform the minimum they could get away with. The worst signal quality/interference issues tended to show up on long runs in rural areas which were generally unprofitable for the cable company (but which they were required to serve in exchange for their monopoly), so they were especially disinclined to deal with them. The FCC had nothing really motivating enforcement (FCC enforces and they catch hell from industry lobbyists), local issues simply do not get traction with national regulators. At least the people in my community had something of a voice, since as a local agency we were forced to be responsive to the community, though our power was not the same as the FCC’s (in some ways we had more regulatory power, in some ways we had less).

    Of course, interference goes both directions.

    Modern PCs are pretty noisy. To get transistors to switch faster you push harder clock driving levels, to keep chips synchronous you use big clock distribution trees and delay lines which create lots of potentially radiating surfaces. Reduce lead solders are more likely to gain semiconducting contaminants over time and produce spurious harmonics. Most modern systems contain a feature called “Clock spread spectrum” which basically adds a ton of phase noise to the system clocks, it doesn’t reduce the noise, in fact it often increases it (by worsening various impedance matches), but it gets the system manufacturers around various regulatory requirements which specify flawed measurement techniques.

    My own computers, even in properly shielded cases, produces interesting birdies all over the electromagnetic spectrum. Equipment in the same room typically produces *much* stronger than the intentional radiators which are far away. The laptops are especially bad. It can be quite challenging to hunt down and correct all the sources of spurious RF. Many years ago I had a cute computer housed in a custom made cardboard case. Operating my jacobs ladder would cause it to reboot or freeze, though I don’t know how much of the RF was conducted via the power lines vs through the air.

    So I think the issue is real, although perhaps not material if you’re neither not conducting radio science (or a HAM), and if you’re running Windows (in which case an occasional extra lockup won’t be noticed over the background noise.

  5. Ed Says:

    eheheh… I have to take one of those jacobs ladders to work one day… Maybe I can give it as a present to my boss.
    More seriously, very interesting stuff guys, since neither me nor my friend live in the u.s. I had no idea your cable tv was like that. Here in the u.k. my cable operator installed top quality cabling at my home, hence my comments. TV here is basically all digital, there are only 4 analog signals. I never experienced any squares or blocks. Fiber optics bring the signal to the kerb, only the last few hundred meters are coaxial.