A question to be answered

The Radio Frequency Interference (RFI) generated by the electrical pulse of a lightning strike is an AM signal so standard AM radio is extremely vulnerable to it.

FM radio isn't impacted because of the modulation method isn't compatible. The FM receivers don't look at the AM signal so they don't pick it up.

What follows is an extremely simplified explanation, not a definitive technical answer, so it probably won't please experts.

The reason is that AM ("Amplitude Modulation") radio works by impressing the audio signal to be transmitted onto a "carrier" wave, so that the "amplitude", or strength of the wave goes up and down in step with the modulating audio signal. In the receiver, the carrier wave is stripped out, yielding the audio signal to be amplified and fed to the loudspeaker or headphones.

The trouble is that lightning and other atmospheric electrical phenomena generate strong radio waves which vary rapidly in their amplitude, so that they are picked up by AM radio sets along with the intended programs, over a wide area, interfering with listening pleasure of radio users. Signals can also come from electrical appliances, badly shielded ignition systems motor cycles, automobiles, welding sets, electric railroads, power lines, military and civil radars, and other sources. These signals get through the input circuitry of AM radios and give rise to hisses, clicks, crackles, bangs, etc in the speaker. With a short wave AM radio you can find not just impulsive interference but also whistles and whines and all sorts of noises.

To overcome these and other problems a new system, FM ("Frequency Modulation") was invented, shortly before World War 2. In this system, the amplitude or strength is kept constant, and the frequency is varied slightly to carry the audio signal. FM is inherently almost immune to the kinds of amplitude varying interference I mentioned before, although many FM sets will pick up noise from a running automobile engine if it is a few feet away.

The frequencies used are generally much higher than AM, so there is room for better quality sound. Also a stereo program can be delivered on one signal channel, which would be very difficult on the AM wavebands.

Hi everybody and thanks. Ok, can we say now that the reason behind non

interference in the case of FM is that the amplitude or strength is kept

constant?

Also, shouldn't these different waves be delivered in each channel for

each radio ?

Am I sound mixed up?

Yes, that radios designed for FM are relatively immune to impulsive interference like lightning.



What does that mean?



Maybe a little.

Hi, thanks contrex. Got that right

Listening to the (SM) radio on earphones while cycling in the city is torturous.