The receivers of modern radio tape recorders can provide reception of FM radio broadcasts for information and entertainment. The correct choice of antenna largely determines the quality of listening to radio broadcasts in stereo. This applies to both fixed radios and devices installed on vehicles. The antennas of the latter should ensure stable operation of the radio when the reception conditions change while the car is moving.
Antennas active and passive
The design features of the antenna device determine the quality of the received radio signal. Antennas are called active, which include additional electronic amplifiers of the received signal. Amplification occurs by active elements - transistors. For their operation, an additional source of constant voltage is required. Foodamplifiers of stationary antennas for the radio is carried out by the voltage of the adapter included in the delivery. Antenna devices installed on vehicles use the voltage of the battery or the engine's running alternator.
Antennas, in which signal amplification is carried out only due to competent design decisions of the designer, are called passive. We can say that an active antenna device consists of a passive antenna and an amplifier that compensates for signal attenuation in the antenna cable.
Fixed radios
Antennas for this class of receivers are made in compliance with all the rules related to the theory of creating antenna-feeder devices. These primarily include the correspondence of the geometric dimensions of the vibrators to the length of the received wave. The ratio ¼ is selected to extract the frequency of the radio station of interest from the air. For the FM band, this value is 0.75 meters. Room dimensions for indoor antennas allow for directional designs with high self-gain.
Car antenna options
When choosing an antenna device for a car radio, you need to decide on the method of mounting it on the car. Car radio antennas can be external and internal. From the outside, the antenna can be mechanically fixed to the roof (by the gutter) or to the rear bumper. An active quarter-wave vibrator, made in the form of a solid metal rod, allows you to provide the best reception quality forcompared to other types of car antennas.
The telescopic cut-in antenna allows, by changing the length of the vibrator, to ensure optimal reception of the selected station. Changing the geometric size is carried out by a special engine. Its operation is controlled by the driver with a button inside the cabin. The presence of an additional electrical device reduces the reliability of the telescopic type antenna.
Using a magnet is the easiest way to secure the antenna to an external surface. This does not affect the corrosion resistance of the coating of the car. The main disadvantage is the low sensitivity of the antenna in the FM band due to the insufficient length of the main vibrator pin. All considered antennas have a circular radiation pattern and do not have selective properties. Their gain is close to unity.
In-car radio antennas are often equipped with a signal amplifier.
The overall gain of this type of antenna device is determined by the amplifier. It acts both for the useful signal and for interference at the operating frequency. The location of the interior antennas is the windshield of the car on the passenger side. Fastening is done with double-sided adhesive tape (adhesive tape).
Connecting Antenna
To connect passive antenna devices to radio tape recorders, a high-frequency connector marked ANT is used. Howconnect the antenna to the radio if it contains an additional signal amplifier? In the case of using a stationary receiver, power to the antenna amplifier can be supplied from the adapter supplied through the low-frequency connector on the active antenna body. The antenna cable is connected to the high-frequency ANT connector of the radio.
If no additional power connector is available, an antenna separator or a DC voltage injector must be used. These devices allow you to use an antenna cable both to power the amplifier with direct current, and to transmit the signal of the radio station from the antenna to the receiver via the ANT connector.
The active car antenna option uses an ISO standard car radio connector.
At the same time, pin 5 of connector "A" is designed to power the active antenna with a constant voltage of +12 V. It is necessary to connect the red (+) wire of the active antenna to it. The black wire is connected to the car body in any convenient place near the antenna. The high-frequency cable is connected to the antenna input of the radio. Sometimes this may require a special adapter.
Conclusion
After reading the material presented in the article, the reader will be able to make an informed choice when purchasing an antenna for the radio. You can now install and connect the selected device yourself. This will not require the use of expensive devices and tools.
