Some people complain of a difficult reception on their radio after replacement of light bulbs with LED bulbs, and even for a reception on the FM band, which normally has the advantage of being insensitive to the parasites. Some disruption is light and does impact the receipt if the radio receiver is located close to the bulb, at other reception of all radio is impossible even at a distance of 4 meters of the bulb!
Without going too far into the details, remember that the modulation of frequency (FM, Frequency Modulation) allows to carry a signal (audio for example) from one point to another (link wired for interphone sector, infrared for headphones hifi wireless or HF for an FM radio) with a low sensitivity or even in the surrounding noise. If the reception of a radio program broadcast in amplitude (AM, Amplitude Modulation) modulation can be disrupted by parasites “relatives” (motor drill, fridge that gets under way, moped passing), the reception of an FM program is however almost insensitive. This relates to the fact that for FM reception, we’re not interested in the frequency variations of the received signal (carrier of fixed amplitude which the frequency is changed by the useful signal), and parasites which are mainly “amplitude variations” are ignored. To receive AM, the receiver is interested in variations in amplitude of the received signal (carrier fixed frequency whose amplitude is modified by the signal), and if a parasite is in addition to the useful signal, he treats it like a useful signal, and you hear it.
Bulb to LED and radio-frequency
A LED light bulb, like all electric or electronic equipment, must meet standards of EMC. These standards have been established to protect equipment against parasites emitted by their neighbours, but also to prevent that themselves don’t disturb their neighbors. These standards are very strict, but are not always respected, mainly for reasons of size (we don’t like the larger units of lamps than the lamps themselves) and for cost reasons (validate EMC equipment, to put him through a series of tests that call for sophisticated and expensive equipment). You will not be surprised (but we can pretend to be) to learn that some LED bulbs are less “serious” than others.
The main problem is that LEDs require a low voltage to operate and that the sector 230 V must be lowered. There are several techniques to lower the tension and some of them (switching power supply simplified to the extreme) cause of vigorous parasitic radiation. Can be addressed very strongly created parasites by using mechanical methods (shape and material of the container) and electric (low-pass filters). But it costs money, so to offer bulbs sector led less than 5 euros, we must make some concessions… In 2011, a LED bulb in three did not meet the EMC standards (source of the federal Office of communications).
But why a disturbance in FM?
Yes, why a receiver propped up on a program broadcast in the band FM 88-108 MHz can be disturbed by noise?
First of all, it should be noted that there are different qualities of radio receiver, and everyone gets home the same amount of energy HF (from the radio broadcast program). A radio (AM or FM) receiver is characterized by several technical parameters that the user don’t often do. It is for the two main, sensitivity and selectivity. Simply put, the sensitivity determines the ability of the receiver to catch a show with a low level of HF, and the selectivity is the ability of the receiver to separate two broadcasts on frequencies close (with quality). A low range receiver exhibits poor performance and is more likely to be disturbed by a fixed frequency signal in parallel of the useful radio show. But parasites emitted by some LED lamps are of a permanent nature and may spread high in the radio-frequency spectrum! I have the memory of a stalled on an FM broadcast radio station which was disturbed by the moped to my brother. It was a slight disturbance, but the link was clearly established (when the moped was moving away, the reception was again perfect) and I did not understand how an “insensitive to the parasites” radio could be so upset!
If in your home you receive the radio on the edge of the possibilities of the receiver, the quality can be good until a parasite comes to turn everything upside down. And this is valid for a low range or high receiver
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