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Radio antenna replacement


Guest xerxes

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Many new cars now sport the small stubby antenna that looks like a fin. Is it possible to use this also for AM-FM radio reception or is there an optimum length / different composition issue? The wind noise off my antenna when I have the top down and radio on is loud and I'd love to have an option.

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There are a lot of weird antennas on new cars these days. They are for satellite radio, cell phones, and GPS. All operate in frequency ranges that are very different from traditional AM/FM broadcasting.

The stock Reatta antenna is approximately a quarter wavelength long in the middle of the FM broadcast band - about 2.5 feet at 98 mhz. Veer too far from this an your FM reception will begin to suffer due to the mismatch. On the AM side, the mismatch is huge already. (A quarter wave at 1 mhz is nearly 250 feet long!) However due to the low frequency, the feedline losses are low and the radio has been designed to cope with the weird impedance presented by the antenna.

A proper 'electrically short' antenna, one that is shorter than 1/10th wavelength, will have a special preamplifier at its base to compensate for the mismatched length and avoid feedline losses. It is how a lot of the 'hidden' receiving antennas work nowadays. Fuba makes a lot of these for the car companies, and also sells them in the aftermarket.

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  • 3 years later...

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