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I local telephone companies will install RF filters for G. REMEDIES FOR RADIO AND TV Can radio waves a fee.) If the device is still under warranty, the RECEIVERS from a base manufacturer might provide an interference filter, station affect my radio or the dealer might take the unit back in In the case of TV or radio interference,the ambient or television set? exchange for another model with better RF immu- strength of an interfering signal is again usually niry.The FCC's Last Licensee On policy does not beyond the control of the person experiencing apply to telephones or answering machines. interference.So the two primary ways to suppress AA strong radio interference are,again,shielding and filtering. wave can cause F. RADIO AND TV RECEIVERS using grounded metal baffles and enclosures to interference to a radio Radio and television receivers respond to RF sig- keep interfering RF fields from reaching the sensi- or television receiver if nals,and interference can result if a receiver tive electronic components inside the tuner or it is strong enough to receiver,and using circuits to block out-of-band overload the receiver responds to an undesired radio signal.No rectifica cion is needed,as is the case with interference to frequencies,or to shunt them to ground without or to overcome the stereo amplifiers and telephones.However,signals weakening the desired signals. receiver's inherent from cellular base stations are rarely involved in There are no government regulations specifying ability to distinguish radio or TV interference. Interference which minimal acceptable levels of shielding or filtering between signals of occurs through overloading of the receiver's RF for radio and TV receivers and FM stereo tuners. different frequencies. circuits is called blanketing. It can occur near an Some radios,FM receivers and tuners,and televi- However, radio waves AM or FM radio or television transmitter. sion sets include no or minimal shielding or filtering; fro„►abase station are Blanketing becomes more likely as the Effective others employ enough to have good RF immunity usually much too weak Radiated Power increases.When blanketing As is the case with audio components,radio and by the time they reach occurs, the audio output from an FM tuner or TV manufacturers assume a certain ambient RF anybody's residence to receiver can be heavilydistorted or sound like field strengthaffect a radio or televi- and design their products to func- gibberish.Sometimes,there is no audio output at tion under those conditions.However,if the Sion receiver. all.A television subject to blanketing can display ambient field exceeds the mar. facturer's assump0 - a faint to moderate herringbone pattern on top of tions,built-in shielding and filtering may be inad- the desired image,alternating black-and-white equate,and more must be added to eliminate the horizontal bars,or,in severe cases,a totally dark interference.The FCC's Last Licensee On policy screen. Blanketing can also affect the television makes a newcomer licensee,for a limited period of ^Can the radio program's audio. time,resolve reasonable complaints of new inter- ( J waves from a Each receiver has a certain selectivity which helps ference to radio and television receivers.However, base station affect my the Last Licensee On policy does not require car's electronic systems? it ignore off channel signals.The better the licensee receiver's design and construction,the greater the s to cure interference to radio or television selectivity,and the greater the receiver's immunity receivers connected to special deep-fringe,high- gain antennas or signal boosters. AS radio waves to out-of-band signals.And the greater the 1g frequency difference between the interfering and H. AUTOMOBILE SYSTEMS can cause inter- desired signals,the better a receiver can tolerate ference to a car's strong interfering signals without succumbing to Today's cars include many electronic devices and onboard electronics in overload. systems.Transducers convert such mechanical much the same way as quantities as coolant temperature,oil pressure, strong signals can FM broadcast tuners and receivers have enough wheel speeds,engine revolutions,throttle opening, affect stereos and tele- selectivity,and cellular operating frequencies are fuel flow,and exhaust emissions into electrical phones. However, far enough removed from the FM broadcast band, signals for processing by electronic brains.The radio waves from a that blanketing interference from cellular base stations signal processors generate control signals in base station are much to FM broadcast reception is very rare.Even response to these variables and thereby control too weak at ground though UHF television receivers are theoretically such items as spark timing,the richness of the level to affect onboard more susceptible (because they are broadband air/fuel ratio,brake-fluid pressure,and cooling fans. automotive systems. devices,and because UHF TV channels are much Also, most car manu- closer to cellular operating frequencies than FM The automotive environment is a very demanding facturers build in a broadcast channels are6),the FCC has no reported one,with great temperature extremes and large good measure of inter- • complaints of interference to TV reception from amounts of mechanical vibration.Automotive Terence immunity. base stations. engineers have made great progress in adapting electronics to the rigors of this hostile environ- 29