I hope many people might feel little awkward to see this question. But I feel this is important. Because in my place where I am living I can get a radio (Audio Receiver) very cheaply. I don't know till what extent they allow the audio frequency ranges. I guess they use ICs for Frequency Demodulators, Frequency Clippers, etc. If the Frequency demodulator doesn't work properly and allows all the frequencies that comes through air then its going to be a big problem to the humans. Can somebody answer which are all the frequency ranges that are available and which causes human hazards?
The short answer is that unless you are dealing with professional power levels in the several watts range, RF is very difficult to cause injury with.
RF doesn't affect humans directly unless there is a tremendous amount of power. Effects are typically thermal, when a particular chemical bond is struck just-so, it will absorb a photon, moving it slightly. Enough heating will damage cells by denaturing or "cooking" proteins.
Particular wavelengths (2.4 GHz) are well absorbed by water and fat, but absorption is still very diffuse so it would take a tremendous dose to cause enough heating in any one area to cause damage. The FCC safe exposure limit is 1.6 W absorbed per kilogram (as per one source), and 4 W/kg (in following link) for the entire body.
- FCC RF Safety FAQ
- Specifically this question which has links to
- the Center for Devices and Radiological Health (CDRH), Food and Drug Administration.
- the Environmental Protection Agency's Office of Radiation Programs
- OSHA guidelines and studies
Atomic nuclei can also also respond to RF, allowing for nuclear magnetic resonance spectroscopy (or MRIs), but this is a strictly nuclear effect and has no influence on chemical bonds.
IR and light obviously can cause burns, but only at sufficient power. IR lasers can be particularly hazardous to eyes, as it invisible it will not trigger a blink or aversion reflex, allowing a large, damaging dose to be absorbed before noticing.
Higher energy photons, UV, X-ray, and gamma, are able to ionize atoms when they strike them, causing unexpected chemical reactions to occur which can destroy, damage, or mutate cells.
These are all forms of "radiation", but the layperson couldn't tell what the implications of non-ionizing versus ionizing radiation are, which causes all sorts of unfounded fears of these invisible phantoms that carry our cell phone calls and webpages.
The question sounds like it's asking: What if a radio "lets through" high frequency (RF) signals into the audio spectrum - will it hurt people to hear audio signals way above (or below) the normal audio spectrum of human hearing? It's not asking about the effects of radio waves on a human.
From an engineering perspective you might translate this as: does the audio amplifier in a radio even try to amplify signals outside the range of human hearing, roughly 20Hz-20kHz? It would be bad if it did, as such behavior can cause components in the radio to run hotter than they would otherwise (wasting battery life and shortening the operating lifespan of the radio) without producing any effect in the audio output that human ears could hear. So a well-designed radio would probably have a lowpass filter before the audio amp to get rid of high-frequency noise, wherever it may come from (not necessarily a broken part upstream in the radio). Whether a very cheap radio would bother with this is questionable.
The next question would be, suppose you tried to drive a speaker with a signal way above the normal audio frequency range - what would happen? Speakers can't respond quickly enough to the signal to generate sounds all that far above audio range. They might be able to reproduce the signal accurately up to 22kHz or maybe 30kHz but much above that and the signal won't be getting made into vibrating air, it'll just dissipate as heat somewhere in the system. You won't get 1MHz audio from a consumer product because the speakers can't reproduce it.
Which is not to say that sound outside the range of human hearing doesn't exist or can't hurt you, just that generally speaking, a consumer radio won't reproduce such sound.