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Black holes of radio reception in San Ysidro and Mount Soledad

Mexican stations and mountain-top transmitters are the problem

Dear Matthew Alice: What causes the “black holes" of radio reception at the international border (Tijuana-San Ysidro) and on top of Mt. Soledad? I travel frequently to both places, and my radio goes berserk every time, alternating between stations without any discernible reason. Whit's creating this transmission turmoil? — Radio Daze, La Jolla/Baja

I’m assuming you’re listening to the FM band, since nobody but reactionary talk-show soreheads and news and sports junkies listens to AM anymore. An FM radio signal (a “line-of-sight” signal) basically travels in a straight line from the transmitter until it bumps into something like a mountain or a building or a car, and then it stops. When you’re tooling along I-5, grooving on the tunes, your radio is pulling in the strongest signal at a particular frequency. Once you get into the border area you’ve come out from behind hills and into an area that’s on the line of sight for a whole bunch of Mexican transmitters, some of which are powerful enough and close enough to the frequency set on your car radio that your tuner starts jumping around, trying to pull in the strongest one. It’s designed to do that, and usually it works to your advantage. (Some of the interference may come from “harmonics” from military or police transmissions in the border area; that’s a sort of ghost interference that occurs at double the broadcast frequency. The full explanation is mind-bending. I’ll leave it at that.) On Mt. Soledad, your radio tuner is being overwhelmed by the signals radiated from the many radio and television broadcast transmitters installed up there. So it’s just chaos in waveland, and your relatively wimpy car tuner has trouble making sense of it all.

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Dear Matthew Alice: What causes the “black holes" of radio reception at the international border (Tijuana-San Ysidro) and on top of Mt. Soledad? I travel frequently to both places, and my radio goes berserk every time, alternating between stations without any discernible reason. Whit's creating this transmission turmoil? — Radio Daze, La Jolla/Baja

I’m assuming you’re listening to the FM band, since nobody but reactionary talk-show soreheads and news and sports junkies listens to AM anymore. An FM radio signal (a “line-of-sight” signal) basically travels in a straight line from the transmitter until it bumps into something like a mountain or a building or a car, and then it stops. When you’re tooling along I-5, grooving on the tunes, your radio is pulling in the strongest signal at a particular frequency. Once you get into the border area you’ve come out from behind hills and into an area that’s on the line of sight for a whole bunch of Mexican transmitters, some of which are powerful enough and close enough to the frequency set on your car radio that your tuner starts jumping around, trying to pull in the strongest one. It’s designed to do that, and usually it works to your advantage. (Some of the interference may come from “harmonics” from military or police transmissions in the border area; that’s a sort of ghost interference that occurs at double the broadcast frequency. The full explanation is mind-bending. I’ll leave it at that.) On Mt. Soledad, your radio tuner is being overwhelmed by the signals radiated from the many radio and television broadcast transmitters installed up there. So it’s just chaos in waveland, and your relatively wimpy car tuner has trouble making sense of it all.

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4S Ranch Allied Gardens Alpine Baja Balboa Park Bankers Hill Barrio Logan Bay Ho Bay Park Black Mountain Ranch Blossom Valley Bonita Bonsall Borrego Springs Boulevard Campo Cardiff-by-the-Sea Carlsbad Carmel Mountain Carmel Valley Chollas View Chula Vista City College City Heights Clairemont College Area Coronado CSU San Marcos Cuyamaca College Del Cerro Del Mar Descanso Downtown San Diego Eastlake East Village El Cajon Emerald Hills Encanto Encinitas Escondido Fallbrook Fletcher Hills Golden Hill Grant Hill Grantville Grossmont College Guatay Harbor Island Hillcrest Imperial Beach Imperial Valley Jacumba Jamacha-Lomita Jamul Julian Kearny Mesa Kensington La Jolla Lakeside La Mesa Lemon Grove Leucadia Liberty Station Lincoln Acres Lincoln Park Linda Vista Little Italy Logan Heights Mesa College Midway District MiraCosta College Miramar Miramar College Mira Mesa Mission Beach Mission Hills Mission Valley Mountain View Mount Hope Mount Laguna National City Nestor Normal Heights North Park Oak Park Ocean Beach Oceanside Old Town Otay Mesa Pacific Beach Pala Palomar College Palomar Mountain Paradise Hills Pauma Valley Pine Valley Point Loma Point Loma Nazarene Potrero Poway Rainbow Ramona Rancho Bernardo Rancho Penasquitos Rancho San Diego Rancho Santa Fe Rolando San Carlos San Marcos San Onofre Santa Ysabel Santee San Ysidro Scripps Ranch SDSU Serra Mesa Shelltown Shelter Island Sherman Heights Skyline Solana Beach Sorrento Valley Southcrest South Park Southwestern College Spring Valley Stockton Talmadge Temecula Tierrasanta Tijuana UCSD University City University Heights USD Valencia Park Valley Center Vista Warner Springs
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