144 MHz car antenna. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / VHF antennas
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The antenna consists of a housing where there is a magnet for mounting it on the car roof and an extension coil. As a magnet, you can use a ring magnet from a sufficiently powerful dynamic head. The body is made of brass and covered with felt on the bottom to prevent scratches on the surface of the car and increase the coefficient of friction.
The extension coil is wound with silver-plated wire with a diameter of 3 mm and has 4 turns with a diameter of 30 mm, stretched to a length of 40 mm. An insulator is installed in the upper part of the body, where a vibrator is installed, made of a brass tube or other material 1180 mm long. The coaxial cable is soldered with a core to the coil, and a braid to the body. It is necessary to ensure that the magnet has electrical contact with the body around the entire perimeter. This can be done with petals. The cable is led out of the housing into a hole in the side wall. The cable must have a characteristic impedance of 50 ohms.
Set up the antenna as follows. Connect it to the radio station. The radio station is turned on for an output power of 0,5 W and put into transmission mode. The radiation of the antenna is controlled by the field strength indicator, setting it at a distance of 8 - 10 meters from the antenna and achieving its maximum readings.
When setting up the antenna, you need to install it on the place of the car where it will be during operation and mark it. The tuning is carried out by stretching and compressing the turns of the coil, while the frequency of the radio station should be 145 MHz. If the radio amateur has a VSWR meter, then the antenna can be tuned and matched with the feeder more accurately.
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