Ask The Old RF Curmudgeon – "What About RF Interference from LED Devices?"
*** If you are new to The Old Curmudgeon series, read the previous blog for a brief introduction.***
LBA asks – “Well, RF Curmudgeon, what do you say to this RF interference and spectrum pollution from the nifty LED devices popping up everywhere? Why I can’t drive through an intersection without LED traffic lights blanking out my FM! And don’t get me started about the LED billboards! Maybe my memory fails (it’s been so long) but didn’t the FCC enforce spectrum purity when we were kids?”
As to your LED transmitter observation, I have only a UHF two-way radio in my car, so I haven’t noticed the “LED effect” on VHF high band. We have plenty of LED traffic lights in my area, so that part of the equation is in place. And don’t forget about all those red LEDs in automobile tail lights now. I haven’t noticed anything from the LEDs directly on FM broadcast channels either, including IBOC stations, but that’s more a reflection of our having such strong broadcast signals in my area of the country.
In answer to your other observation, yes, the FCC doesn’t give a twiddly-damn about the RF spectrum or its purity. I think that this trend started well over a decade ago, and it is fueled by two deeply-held policy positions within the Commission. First, they badly want to get out of the regulatory enforcement business. They don’t get any major brownie points or funding from Congress for running the Field Enforcement Bureau (or whatever it’s called now), spectrum enforcement is a bottomless pit for them, and it’s a never-ending chore. They would rather auction the spectrum off and tell the happy purchaser, “You look after the cleanliness of *your* bands! We’re outta here!”
The second is the deeply-held regulatory notion that “cellular transmission” with its concurrent frequency re-use is the highest and best use of the spectrum. If you do cellular, you don’t have to worry too much about the ambient noise level as the transmitters are always fairly proximate to the users. The cellular regulatory model is at work not only in public land mobile, but also in private land mobile (where it’s very difficult to get new PLMRS licenses for wide-area mountaintop or major tower stations, and if you do get one about the most station you can then run is “walkie talkie” power levels. And in broadcasting (LPFMs and LPTVs, which also conveniently use up all available channel slots). And in unlicensed consumer Part 15 wireless LANs. “Et cetera, et cetera, et cetera,” as the King of Siam would say.
Don’t know whether you caught it at the time, but a few years ago the Commission floated an NPRM which proposed to *allow* interference sources onto licensed channels (in this case, microwave), using a concept known as the defined “Interference Temperature!” The idea was that “smart radios” in the interference generator source would “know” when the source had gone one bridge too far and would then shut itself down. Lacking that degree of equipment capability by the interferers, the licensee of the channel could always monitor and scream when the measured “interference temperature” rose past established limits.
The industry quickly shot that *^@(&^ idea down!
So, driven by these two philosophical points, the Commission now says, “Please proceed to trash the spectrum with lots of unlicensed low power devices, singing power lines, chirping power meters, high speed digital logic with femtosecond switching times (I exaggerate, but not by much!), screeching LEDs. We don’t care, and we don’t enforce the law here in Dodge City any longer!”
As soon as some clever businessman figures out a use for the 4 degrees Kelvin cosmic microwave background radiation, it too will be quickly licensed and eventually auctioned off.
You and I, being old timers in this art and science, understand the invaluable resource that the RF spectrum represents and we respect it and we do what we can to maintain it in good working shape. The Commission, especially in later years, has been directed and run by lawyers, economists, and politicians who don’t know the physics behind electromagnetic transmission, have none of the “vision thing” for the future non-economic uses for which quiet spectrum could be employed, and consider the spectrum mostly as an exploitable economic good. What would you expect?
Adding to this outrage, there is too much transference of communications today from wired to wireless modes. Most people don’t really need “Web service to the belly-button!” Now my eleven year-old granddaughters are getting their own cell phones. Give me a (&#%$@& break!
Many, many services could be well and cheaply provided by wire, if we just had a broadband Universal Fiber Network in this country. But that’s yet another Commission failure in the “vision thing.” The Asians and perhaps the Europeans will “clean our clocks” on this failure alone.
So, sayonara RF spectrum, my dear old love! I will always remember you as you were in those long-ago days when you were still young, fresh, and beautiful.
“Let’s keep the universe safe for RF!”
The Old RF Curmudgeon