Bodywork, Paint, Interior, Trim, & Wiring

For those looking for a hidden antenna, check out "tune trapper". I tried a couple of small amplified antennas with no real luck - got lots of static and weak station tuning. A friend told me about tune trapper so I gave it a try. I was skeptical but was pleasantly surprised. It's not quite as good as a fender mounted antenna, but it is WAY better than any others I tried. I get good reception on most stations now! Just thought I'd share the info.

Tuned helical dipole. What that means is that the antenna uses two elements, one connected to the antenna input and the other to ground. Those elements are cut to match the wavelength of FM radio, probably somewhere around the center frequency. Finally, each element or wire is wrapped around a form to make it like a spring with no coils touching, in order to compress the antenna into a shorter space. Antennas have to be an even fraction or a multiple of the wavelength. The longer they are, the more effective. For FM I think 1/4 wave is typical but would have to look it up to be sure. The single aerial antenna is an omnidirectional monopole mounted above a ground plane (the car body).

It is a directional antenna so it will receive better if it has one end pointed at the radio station. The small wire antenna taped to the inside of the windshield is the same thing only not coiled.
The steel of the body will tend to cut down the signal if it is mounted inside the car. Also, since the RF section of the receiver is not made for a dipole, one side is grounded to the body or ground plane, which may reduce the antenna's effectiveness somewhat. These antennas are very often used on portable FM radios, where they look like a black rod or cylinder either inside or outside of the cabinet and may be dipole or monopole designs. It would be quite possible to cannibalize one of these to use as an FM antenna in a car, though it would not be as effective as a monopole.

Jim