The vast majority of car stereos designed for the reception of radio stations in VHF (FM) range. Ultrashort wave with properties very similar to waves of light range: they are propagated in straight lines, are reflected from surfaces, or absorbed by them, and in case of change of the density of the conducting medium is refracted.
For this reason, the broadcast range FM-band is typically around 100 km, and in the case of pronounced terrain – and less. The strength of a radio signal diminishes not only with distance from the transmitting center, a negative impact on the passage of radio waves is also influenced by precipitation, magnetic storms and increased solar activity.
The quality of the received radio signal is markedly influenced by the presence of nearby high-rise buildings, bridges and overpasses. Contribute to industrial enterprises and power lines, generating electromagnetic waves — the so-called "industrial noise".
Another source of such "noise" may be radio interference generated by the onboard network of the car. An electrical discharge generator and high-voltage ignition cables are able to distort even the most high-quality radio signal.
If you think that the deterioration in the quality of radio reception all of the above factors have no relationship, it's time to care about the choice of new car antennas.
Active car antennas equipped with a radio and amplifier ensure reliable reception in the city and beyond it. Due to the fact that active antennas are installed in the car interior, they are protected from mechanical damage and the external environment (sun, temperature changes and precipitation), therefore, have a significantly greater service life than an external passive antenna.
The most common place to install internal antennas are the window frames, the windshield or rear shelf. The choice of location of the active antenna depends on you, as long as it's visibility is not impaired and was placed on a metal surface, since in this case the sensitivity will be reduced significantly.
External antenna is a telescopic or spring-loaded pin and is attached to the outside of the car body. Ways to mount the passive antenna a few: set in drilled in the back of the hole, the pin fixation method to drain and mounting with a magnet.
For perfect reception of ultrashort waves the length of the passive antenna should be equal to the wavelength of the FM band (about 3 m) or a half (1.5 m) or quarter (0.75 m). The efficiency of the external antenna is not dependent on the distance at which it is located from earth, the decisive factor is its height relative to a conducting surface, in this case – to the surface of the car body.
The use of an external antenna is preferred in cases where the bulk of your traffic make road trips outside the locality — sensitivity of the majority of the passive devices is still higher than that of active antennas, despite the loud advertising statements of manufacturers last.If the radio reception in the car has deteriorated significantly, do not rush to blame the antenna, first make sure there is no interference from the vehicle electrical system, check the quality of connectors and connecting cable.
Good luck to you! No nail, no wand!