Ministry of higher and secondary special education of the republic of uzbekistan uzbek state world languages university

Medium range FM interpretation systems (handheld)
These sys­tems use radio waves to trans­mit the speech (ei­ther orig­i­nal or trans­lated) to the at­ten­dees. Just like in­frared sys­tems, FM sys­tems are also con­nected to multi-chan­nel re­ceivers with head­phones.

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  FM systems are portable – light and easy to carry around.
  
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  Unlike infrared systems, FM systems are not sensitive to obstructions, meaning they can penetrate walls and other opaque objects. They're also not sensitive to light, and work well outside.
  
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  Their portability comes with a more limited range though (around 250 feet).
  

FM broadcasting is a method of radio broadcasting using frequency modulation (FM). Invented in 1933 by American engineer Edwin Armstrong, wide-band FM is used worldwide to provide high fidelity sound over broadcast radio. FM broadcasting is capable of higher fidelity—that is, more accurate reproduction of the original program sound—than other broadcasting technologies, such as AM broadcasting. It is also less susceptible to common forms of interference, reducing static and popping sounds often heard on AM. Therefore, FM is used for most broadcasts of music or general audio (in the audio spectrum). FM radio stations use the very high frequency range of radio frequencies.
Modulation
Fre­quency mod­u­la­tion or FM is a form of mod­u­la­tion which con­veys in­for­ma­tion by vary­ing the fre­quency of a car­rier wave; the older am­pli­tude mod­u­la­tion or AM varies the am­pli­tude of the car­rier, with its fre­quency re­main­ing con­stant. With FM, fre­quency de­vi­a­tion from the as­signed car­rier fre­quency at any in­stant is di­rectly pro­por­tional to the am­pli­tude of the (audio) input sig­nal, de­ter­min­ing the in­stan­ta­neous fre­quency of the trans­mit­ted sig­nal. Be­cause trans­mit­ted FM sig­nals use more band­width than AM sig­nals, this form of mod­u­la­tion is com­monly used with the higher (VHF or UHF) fre­quen­cies used by TV, the FM broad­cast band, and land mo­bile radio sys­tems.
The max­i­mum fre­quency de­vi­a­tion of the car­rier is usu­ally spec­i­fied and reg­u­lated by the li­cens­ing au­thor­i­ties in each coun­try. For a stereo broad­cast, the max­i­mum per­mit­ted car­rier de­vi­a­tion is in­vari­ably ±75 kHz, al­though a lit­tle higher is per­mit­ted in the United States when SCA sys­tems are used. For a mono­phonic broad­cast, again the most com­mon per­mit­ted max­i­mum de­vi­a­tion is ±75 kHz. How­ever, some coun­tries spec­ify a lower value for mono­phonic broad­casts, such as ±50 kHz.^[5]