Antenna Selection For VHF/UHF Amateur Communication-Part 2 Car Antenna

Antenna Selection For VHF/UHF Amateur Communication-Part 2 Car Antenna


Vehicle antenna refers to the communication antenna designed to be installed on the vehicle. The most common and most commonly used is the suction cup antenna. Because the suction cup antenna is easy placed and installed, so some fixed amateur stations also often use the suction cup antenna. There are other antennas for other installation methods, such as clips.

A clip-side antenna mounted on the rain edge of the window, and a glass side-mounted antenna that is capacitively coupled by a conductor on both sides of the window glass.

Because the vehicle itself is limited in height, and the antenna that is too bulky will encounter a large wind resistance when the vehicle is traveling at a high speed, the vehicle is highly increased.

The size of the antenna is different depending on the operating frequency band. The vehicle antenna structure is also shortened (including the central plus), and the quarter is wavelength, five-eighth wavelength, double-half-wavelength coaxial array, etc. Antennas of the same working frequency increase in sequence, they are theoretical.

The efficiency and nominal gain also increase in turn, but due to the different manufacturing processes and improved forms, the gain index may differ slightly from the theory. shorten”

The antenna is small in size but not high in gain. Generally, a five-eighth wavelength high-gain antenna has a plus at a distance of one-half wavelength from the top of the antenna.

The sense coil, the double half-wave coaxial array has two sense coils. The five-eighth wavelength antenna and the central plus-sensing antenna are cheaper.

And the gain is higher than that of the quarter-wave antenna, so it is widely used. Some models have springs in the lower part, which can prevent certain antennas hit the effect.In the case of use as a temporary fixed-station antenna, the height of the antenna is not limited and a high-gain type car suction cup antenna should be used. Due to suction the disk antenna is designed according to the environment in which the car is used. Therefore, when it is used as a fixed device, the area to be sucked under it should be larger than the diameter of the inner product circle as the working frequency band.

Metal plates of a wavelength (such as iron sheets) will have better practical use. The shape and gain of the antenna are often considered more often during the antenna selection phase.

Sometimes the manufacturer’s nominal gain has a significant difference from the actual gain, so it is necessary to compare the gain of different antennas by actually testing the antenna samples.

The test method can refer to the comparative field strength test method of the handheld antenna without a professional instrument, and the test environment should simulate the vehicle environment. Due to the car output power of the radio is large. In addition to the test field strength, the SWR (stationary wave ratio) value of the antenna is also tested using the standing wave ratio table. The closer the standing wave ratio is to 1, the more Ideally, the general antenna standing wave ratio should not be greater than 2. Excessive VSWR not only affects the launch but also causes damage to the radio transmitter.

Post time: Nov-01-2019