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• Can radio waves effect on operations,because other than FMtuners, Some consumer electronic devices include little from a base stereo components are designed to respond only or no shielding or filtering.Others employ mean- station affect my tele- to AF signals,not RF signals. However,active ingful amounts.No government regulations specify phone or answering components can inadvertently act as detectors minimal acceptable levels of shielding or filtering machine? that convert RF signals into AF signals.Once for stereo components.5 Manufacturers usually detection happens, the system can no longer assume a certain average ambient RF field distinguish between the desired audio program strength,and design their products to function AA strong radio material and the undesired signal extracted from under those conditions.However, if the ambient wave can cause the intercepted radio wave (such as your CB field exceeds the assumed value,any built-in interference to a regular neighbor's voice). shielding and filtering may be inadequate. telephone e or ng Interference in a stereo system typically arises when Additional after-market measures must be taken system if an electronic the wires runningto the to eliminate interference.The FCC has a"Last component in the speakers pick up radio p Licensee On"policy which makes a newcomer device converts the signals.Speaker cables can be 10 or more feet long, who has set up a radio transmitter responsible for radio wave into an and can inadvertently act as fairly efficient receiving resolving reasonable complaints of newly arising audio-frequency sr antennas.Recovered RF current can pass back g7tQl through the amplifier's speaker-output terminals interference to radio and television receivers— However, as is the case and through the feedback loops to the amplifier's for a limited period of time.However,the policy with potential interfer- weak-signal(input)section. If the ambient RF does not require licensees to cure interference to ence to stereo systems, field and recovered RF current are strong enough, audio equipment(other than FM tuners as dis- the radio waves from a a transistor in the amplifier's input section can cussed below). - base station are much detect or rectify the RF current and extract any E. TELEPHONES too weak by the time audio-frequency information they reach ,, ybody's Y riding on the carrier. The detected audio passes back out through the Modern telephones and telephone answering +tesidence to zffect various amplifier stages,getting stronger along the machines contain electronic circuits,but many elephone equipment. way,until heard through the have little or no shielding.Verylongwires con- g loudspeakers.This is audio rectification interference. nect such devices to the public telephone net- - ..- - work,and such wires can act as efficient anten- It usually takes an RF field of several volts pernas for RF energy.Also,the wires in a cord sev- = L.- meter for such interference to arise.Fields as strong eral feet long that might run between the hand- - -- as that exist only very close to a transmitting piece and the phone body can also act as anten- antenna.A stereo system is hardly ever that close nas.Not surprisingly,telephones and answering to a cellular base station antenna,so audio rectifi- machines can be vulnerable to audio rectifica- cation interference involving signals from base tion interference.One Symposium participant stations is very rare.4 with extensive field experience in the deploy- D. REMEDIES FOR AUDIO SYSTEMS ment of base stations remarked that interference to consumer-grade telep ones was the most fre- Usually,in home settings,the strength of an inter- quent interference problem he had encountered, fering signal is beyond the control of the person although interference involving base stations whose equipment is experiencing interference.So does not appear to be widespread. the two primary ways to suppress audio-rectification Just as in home stereo interference, it usually interference are shielding and filtering. takes a strong RF field for such interferen:e to Shielding sensitive electronics with grounded arise.So those problems which do arise generally metal baffles and enclosures prevents interfering occur if telephone wires nm close to a transmit- RF fields from reaching susceptible components. ting antenna.The remedies are shielding and fil- Electric fields cannot pass through such metal tering,just as with home stereo system compo- shields,and that blocking action prevents RF nents. If someone has purchased a telephone currents from arising that could otherwise disrupt subject to interference,the responsibility for circuit operations.Filtering employs circuits to solving the problem lies with the purchaser,not 40 pass desired frequencies and block undesired ones, the local telephone company. (However,many or to short out undesired frequencies without weakening desired ones. 28