Winner of Name that Ware September 2007!

Last month’s challenge was not necessarily to name a particular device, but rather to name the type of device that generates a class of audible interference. You can listen to the sound again if you need your memory jogged!

While many immediately recognized the sound as interference caused by a GSM or EDGE phone, Jered wins the prize for his very precise analysis of the root cause of the noise:

The reason for the buzz is the nature of time-division mulitple access (TDMA). In the US, we operate mobile phones at 850 Mhz and 1900 Mhz; in Europe, 900 Mhz and 1800 Mhz. Good so far; that’s not going to make noise that we can hear. TDMA fits more subscribers into the same bandwidth by assigning different terminals different timeslots (vs. CDMA, which uses black magic). These timeslots happen to be spaced 4.615 ms apart, yielding a signal envelope which looks a lot like a dirty 217 Hz square wave.

All sorts of things (like “wires”) are good at picking up a 217 Hz square wave at 0.5 W, and 217 Hz is conveniently smack dab in the middle of our auditory capabilities.

Congratulations Jered! Email me for your prize.

I thought this noise was noteworthy because a surprising number of people do not realize where it is coming from. I’ve often heard this noise on conference calls, and its fairly obvious that some participants don’t understand that their cell phone is causing this interference. The thing that befuddles most is the range at which this interference can occur: their phone could be well across the table, yet with the proper antenna orientation, the noise is loud and clear. Often times, the problem can be ameliorated simply by rotating the phone by about ninety degrees.

What disturbs me about this noise is that it’s a prominent reminder of exactly how powerful this RF transmitter is that I happily stick next to my cerebral cortex and my gonads on a daily basis. 0.5 watts is not a trivial amount of power! And of course, Bluetooth hands-free sets are not much better. Granted the power is lower, but Bluetooth operates at 2.5 GHz — and it’s no mistake that microwave ovens also run at that frequency, as it is absorbed particularly well by the water that makes up 60% of our mass.

While there is no conclusive evidence that cell phones cause any sort of biological harm, there is precedent for entire societies that have fallen victim to the myopic use of technology to better life. For example, even a child can tell you today that lead causes poisoning and brain damage…and so we remark at the Roman’s folly: “Gosh, what idiots! They sweetened their wine with lead and used lead pipe to deliver drinking water. Duh, of course the Roman empire collapsed.”

I often wonder if a millennium from now, people will read about us as we do about the Romans. “Gosh, what idiots. They stuck half a watt of radiation on their heads every day for decades at a time. No wonder they all died of debilitating brain disease.” Or, my other favorite is, “Gosh, what idiots! The made their clothes, cars, and even utensils out of plastics. Everyone knows that plastics outgas damaging free radicals. No wonder they all died of cancer”…and in the end, the meek did inherit the Earth.

Then again…there is no conclusive evidence that anything we do really causes that much damage. We’ve learned from the Romans and gotten more clever, and we use “model” organisms and sophisticated extrapolation mechanisms. But then again, those are just models, and there’s no such thing as accelerated lifetime testing on a real human being…and as any engineer knows who has done a lot of reliability testing, there’s always that one corner case that gets through (e.g., the Xbox360 Red Ring of Death). So with enough new technology entering our lives, the chance that we’ll encounter unforeseen consequences goes up and up. You and me — we’re the ultimate guinea pigs in this grand experiment with technology!

5 Responses to “Winner of Name that Ware September 2007!”

  1. In truth, half a watt isn’t that much. Just because the noise can cross a room, and be picked up by an audio amplifier means very little. The thing is, there just isn’t enough energy to do anything. In many cases, the signal being picked up could be in the microvolts and you’d hear it. That doesn’t mean that the RF will have a measurable physiological effect.

    Now, if you want to see scary RF, just look at a 1kW transmitter:) Touching the antenna at *that* power level can kill you.

  2. Dustin says:

    I remember a few years ago I had a crazy nextel phone at work that you could tell anytime it was going to receive a call, since all the speakers at workstations in 5 or 6 nearby cubicles would go crazy about 2 seconds before it would actually ring. Also good for meetings.

  3. The bit about 2.5 GHz being particularly well absorbed by water is a myth; there’s nothing special about that frequency. For more details, see:

  4. Rick says:

    Hard to say whether 500 mw is a big deal or not. Another take on
    your comment:

    From the movie “Sleeper”:

    Dr. Melik: This morning for breakfast he requested something called “wheat germ, organic honey and tiger’s milk.”

    Dr. Aragon: [chuckling] Oh, yes. Those are the charmed substances that some years ago were thought to contain life-preserving properties.

    Dr. Melik: You mean there was no deep fat? No steak or cream pies or . . .hotfudge?

    Dr. Aragon: Those were thought to be unhealthy . . . precisely the opposite of what we now know to be true.

    Dr. Melik: Incredible.

  5. bunnie says:

    Huh, thanks for the clarification about the 2.5 GHz and water. I knew that it was an ISM band because it was crappy for terrestrial communication due to the absorption of the frequency by water (of course they give to the public good the tailings of the spectra that industry would not buy) — didn’t realize it was water vapor only that absorbed it. I stand corrected!

    Also, yes — 0.5W isn’t that much power in the grand scheme of things. I didn’t want to give the impression that I’m discouraging people to use their phones; I still use mine all the time, and I eat trans-fat all the time too (but I also believe in regular exercise). However, there’s just that nagging sense of maybe we’re missing something important somewhere in our tangle of assumptions about what’s safe or not, especially when it comes to prolonged exposure. Complex systems are not always so cleanly abstracted…