A colleague of mine at Electronic Design, Ron Schneiderman, wrote me recently asking about a mysterious wireless problem he was having. When he parks his Volvo in the garage, the remote keyless entry system that opens the doors and trunk won't work. Back the car outside, and voila' it works like a champ. It seems like Ron's garage is a wireless dead zone or cone of silence...or something.
Ron is knowledgeable wireless guy, as he has written about it for years for another publication. And I have an extensive wireless background editorially and engineering wise. Yet, neither one of us has come up with a valid explanation. Most of these remote keyless entry devices operate in the 315 MHz range, so my first thought was that maybe his garage door opener (also usually in the 315 MHz range) receiver local oscillator was jamming it. But that was not it. And there are no other wireless devices except for AM and FM and XM satellite radios in his other car or garage, all of which are off.
So what is it? In searching for an answer, Ron noticed his home security system acting funny. So he had an expert come check it out. Sure enough, the window sensors are wireless in the same 315 MHz frequency range. They all needed batteries and were re-acting funny with the security base station. New batteries and a reset of the system solved the problem.
We are getting so many wireless devices in our lives now we not only have to tend with each one individually but how they interact with one another. A real....and growing....EMI problem with unlicensed short range products. Something to keep in mind if you are designing or deploying a product or system.