I've heard that "rubber duck" antennas shouldn't be used inside an automobile. What is the reason for this, and are there any other types of antennas that shouldn't be used inside a vehicle?
From test pool question: T9A07
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There's nothing particularly wrong with them. Cars, being mostly made of metal, do a pretty good job of shielding any RF signals, which is why you probably get worse reception when your HT is in your car. It doesn't help that rubber duck antennas aren't that good to start with - they are "electrically short", meaning that they are shorter than a true quarter wavelength, and they are monopoles, meaning that there is no "counterpoise" or "ground return" like in a dipole antenna.
Rubber duck antennas just perform worse than an ideal antenna, especially in a car. But that said, that hasn't stopped me from using my Wouxun with a rubber duck from inside my car, or a Motorola HT from inside an ambulance without any problems. Nothing terribly bad will happen, it's just not as good as using a real mobile radio with a real mobile antenna mounted to the roof of your car.
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$\begingroup$ There is a counterpoise and a ground return: the body of the HT, the operator's hand, and Earth. The problem is that there isn't an especially good ground return, a deliberate design trade-off between size and efficiency. $\endgroup$ Nov 19 '13 at 19:36
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$\begingroup$ Capacitive coupling through the plastic HT case isn't what I would call a solid ground, but I do see yout point. $\endgroup$ Nov 20 '13 at 0:33
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$\begingroup$ I use my Baofeng UV-82 HT in the car with the rubber ducky and it works fine for about 5-10 miles, but this depends on car and whatnot, but with a half wavelength mobile antenna on 2m I can hit almost 30 miles with the 5W HT. $\endgroup$– DanNov 21 '13 at 17:59