Unless you are over a certain age, you probably take it for granted that electronic gadgets you buy have some FCC marking on them. But it wasn’t always true. [Ernie] submits that the FCC’s regulation of the computer industry was indirectly the result of the success of CB radio in that same time period.
Today, there is a high chance you don’t watch TV directly over the airwaves or even consume audio from a traditional radio station. Even if you do, the signal is increasingly likely to be digital. But only analog radio and TV were highly susceptible to interference. When a professional radio station or the power company interfered with you watching I Love Lucy, you could count on them to resolve it. Even ham radio operators, a small segment of the population, would, in general, graciously help you if their transmissions interfered with your equipment.
Never mind that, in many cases, it was the cheap TV or some other problem on the receiving end. Then there was another source of potential interference: CB radio. At first, you were about as likely to encounter a CB operator as a ham radio operator. But then in the 1970s, CB exploded, becoming a cultural phenomenon, and you can hear what a state it was in by watching the contemporary TV report in the video below.
This explosion of operators who did nothing more than apply for a license (if they even bothered to do so) and bought their equipment at a local store had no idea how to help curb interference, even if they wanted to. In 1977, the AP reported that 83% of the FCC’s TV interference complaints involved CB radio.
Early computers were also very noisy on the radio bands. So much so that early attempts at computer audio output were simply modulating the radio frequency interference. Again, at first, this wasn’t a huge problem. But as computers became more common, so did computer-related interference, and the FCC didn’t want to deal with another CB radio-style explosion.
The rest is, as they say, history, and [Ernie] covers it all in the post. Getting a product approved by the FCC isn’t trivial, but if you have to do it, we have some advice.
When I first started programming in the early 1970s I remember writing BASIC programs that could play tunes on a handheld AM radio held near the computer by controlling the instructions and number of repetitions in nested loops. That was on a PDP-11 IIRC.
I spent a significant part of my career in EMI testing chambers with various products I designed. There are strict limits on how much RF can be emitted by digital devices, and some of my best memories are of finding the cause of noncompliant emissions and putting in the fixes to get the devices to pass.
The last device I worked on was for a client, and included a DC motor. We determined that the noncompliant energy was associated with the motor when it was driven under load, but the design was exactly the same as a prior device that had passed. The polarization of the emissions was vertical, indicating that the energy was radiating off the metal body of the tall, skinny device. We tried everything, including an embarrassing number of ferrite beads. No luck. At literally the last minute (our time in the chamber was almost up, and this was the third visit), I noticed two capacitors between the motor leads and chassis ground…part of a Pi filter. “What the hell, let’s pull them,” I said, being out of ideas, and knowing that these caps were in the earlier device. Bang! The noncompliant emissions dropped by 20dB!
Just because it worked before, doesn’ mean it’s going to work again. The prior device used a lower voltage power supply and a slightly different motor.
I should note that EMI limits are global, not just FCC. There are subtle differences depending on what standards a country uses, but they’re all pretty much the same. The regs also vary by equipment type and application — medical equipment is different than aviation equipment for example.
And hardly anyone watches broadcast TV any more…but you definitely don’t want your equipment interfering with aviation communications, which is in nearby frequency bands. The FCC will hunt down signals in that band pretty aggressively.
Ummm … Square waves have harmonics. All these digital signals spew garbage into the ether and raises the noise floor making it harder to communicate over the airwaves. A higher noise floor reduces range and interferes with what is trying to be transmitted over it. To overcome this you have to transmit at a higher power which raises the noise floor even more. This is the main reason today you see regulatory bodies concerned about computers.
The FCC should address the importation and sale of LED ceiling lights from China. Many come with a false FCC logo on the box, but every one that I’ve installed has created significant interference with my broadcast TV reception, because the ceiling light location is just a few feet (and a few walls) away from my exterior aerial. I get no such interference from a fixture in the same location using dimmable LED A21 bulbs.