[kwlug-disc] To WIFI or not to WIFI

[Andrew Kohlsmith (mailing lists account)]

> So let’s do an experiment:
> 1. Get a cheap ($15) radiation dosimeter
> 2. Measure the background radiation (e.g. ticks/minute if it doesn't have an LED readout)
> 3. Put it next to a cell phone playing a video across cellular data (4G/5G LTE) & measure the ticks/minute
> 4. Put it next to a cell phone playing a video across WiFi (802.11n/ac/ax) & measure the ticks per minute
> 5. See whether 4G/5G LTE and/or 802.11n/ac/ax generate more than 15 times background radiation.

#1 is likely to be the issue here — That dosimeter is quite likely to be both uncalibrated and quite susceptible to EMI/RFI, and will most definitely not have any kind of traceability in its calibration.

The sensor in such a unit will most likely be any old run of the mill MOSFET; the theory behind its operation is sound, but different physical parts will have different response characteristics, and even identical parts in different manufacturing lots can have dramatically different responsivity. An inexpensive unit is very unlikely to have any kind of QC regarding the sense MOSFET.

Beyond the sensor itself, the amplification and analog processing of the very tiny signals from the sensor are unlikely to be carefully designed to reject regular old non-ionizing radiation. Most of us are old enough to remember how keeping your old GSM cell phone next to unshielded speakers could induce a particular buzzing effect when the phone’s radio was keyed up, or even how touching the tip of a 1/4” patch cord of a guitar amplifier could induce a hum. This is the same effect as what I’m describing when I talk about the unit being susceptible to EMI/RFI. It’s not actually responding to an increase in ionizing radiation, but rather to harmless electrical noise. Both cellular radios and wifi radios can induce currents in nearby circuitry which would be misinterpreted by cheap amplifiers, and when those amplifiers are connected to an inexpensive dosimeter they will yield a false increase in the measured ionizing radiation.

I design complex and sensitive electronic devices for a living; it’s important to be mindful of the “obviousness” of simple scientific experiments which lack any kind of rigor or control.

-A.

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