Open hailing frequencies

By Bunnie Huang. Posted

There’s a lot to be happy about when looking at the new the Raspbery Pi 3B+ – faster CPU, faster connectivity, PoE support, all for the same price tag. However none of those things got me as excited as the fact that the 3B+ has been compliance tested as a radio module.

I know what you’re probably thinking – ‘compliance testing’ sounds incredibly mundane, how could anyone get worked up over that?

Most governments publish a set of strict wireless emissions standards that every consumer product must comply to in order to be sold. The problem is these standards were written decades ago, when AM radio was common. AM is very ‘fragile’; minuscule amounts of stray noise will affect it. And so, laws were passed decades ago that codified tests designed to protect these ancient devices.

The tests themselves can be gruelling; testing a non-modular WiFi ‘active transmitter’ requires a custom firmware blob that forces the transmitter to send continuous signals in every possible modulation over select frequency bands. You’ll be required to solder a connector in place of the antenna on the PCB for some of the tests. These tests can cost thousands of dollars to execute at an approved facility, and delay projects by weeks or even months.

Unfortunately, no amount of regulation can protect something as fragile as AM; so, technology progressed to more interference-robust standards like FM or, more recently, spread-spectrum techniques such as OFDM. Yet the emissions standards – hard-coded into law – were never revised to reflect these ground shifts in technology. So here in 2018, we’re expending a disproportionate amount of time and effort designing counter-measures to protect these now-defunct radio applications.

By certifying the Raspberry Pi 3B+ as a ‘radio module’, Raspberry Pi has already passed the most onerous tests on our behalf. So long as we don’t modify the Pi’s radio function or design, products incorporating the Raspberry Pi 3B+ as a radio module are now subject to a greatly abbreviated series of tests. The metal shield over the radio circuitry, along with other more subtle counter-measures, also means there’s more headroom for the noise that will be generated by our application-specific circuits and peripherals. Overall, this will save numerous hackers, engineers, and startups thousands of dollars, countless sleepless nights, and weeks on already too-tight delivery schedules.


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